/*
 * Copyright (C) STRATO AG 2011.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

/*
 * This module can be used to catch cases when the btrfs kernel
 * code executes write requests to the disk that bring the file
 * system in an inconsistent state. In such a state, a power-loss
 * or kernel panic event would cause that the data on disk is
 * lost or at least damaged.
 *
 * Code is added that examines all block write requests during
 * runtime (including writes of the super block). Three rules
 * are verified and an error is printed on violation of the
 * rules:
 * 1. It is not allowed to write a disk block which is
 *    currently referenced by the super block (either directly
 *    or indirectly).
 * 2. When a super block is written, it is verified that all
 *    referenced (directly or indirectly) blocks fulfill the
 *    following requirements:
 *    2a. All referenced blocks have either been present when
 *        the file system was mounted, (i.e., they have been
 *        referenced by the super block) or they have been
 *        written since then and the write completion callback
 *        was called and a FLUSH request to the device where
 *        these blocks are located was received and completed.
 *    2b. All referenced blocks need to have a generation
 *        number which is equal to the parent's number.
 *
 * One issue that was found using this module was that the log
 * tree on disk became temporarily corrupted because disk blocks
 * that had been in use for the log tree had been freed and
 * reused too early, while being referenced by the written super
 * block.
 *
 * The search term in the kernel log that can be used to filter
 * on the existence of detected integrity issues is
 * "btrfs: attempt".
 *
 * The integrity check is enabled via mount options. These
 * mount options are only supported if the integrity check
 * tool is compiled by defining BTRFS_FS_CHECK_INTEGRITY.
 *
 * Example #1, apply integrity checks to all metadata:
 * mount /dev/sdb1 /mnt -o check_int
 *
 * Example #2, apply integrity checks to all metadata and
 * to data extents:
 * mount /dev/sdb1 /mnt -o check_int_data
 *
 * Example #3, apply integrity checks to all metadata and dump
 * the tree that the super block references to kernel messages
 * each time after a super block was written:
 * mount /dev/sdb1 /mnt -o check_int,check_int_print_mask=263
 *
 * If the integrity check tool is included and activated in
 * the mount options, plenty of kernel memory is used, and
 * plenty of additional CPU cycles are spent. Enabling this
 * functionality is not intended for normal use. In most
 * cases, unless you are a btrfs developer who needs to verify
 * the integrity of (super)-block write requests, do not
 * enable the config option BTRFS_FS_CHECK_INTEGRITY to
 * include and compile the integrity check tool.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/buffer_head.h>
#include <linux/mutex.h>
#include <linux/crc32c.h>
#include <linux/genhd.h>
#include <linux/blkdev.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "extent_io.h"
#include "volumes.h"
#include "print-tree.h"
#include "locking.h"
#include "check-integrity.h"
#include "rcu-string.h"

#define BTRFSIC_BLOCK_HASHTABLE_SIZE 0x10000
#define BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE 0x10000
#define BTRFSIC_DEV2STATE_HASHTABLE_SIZE 0x100
#define BTRFSIC_BLOCK_MAGIC_NUMBER 0x14491051
#define BTRFSIC_BLOCK_LINK_MAGIC_NUMBER 0x11070807
#define BTRFSIC_DEV2STATE_MAGIC_NUMBER 0x20111530
#define BTRFSIC_BLOCK_STACK_FRAME_MAGIC_NUMBER 20111300
#define BTRFSIC_TREE_DUMP_MAX_INDENT_LEVEL (200 - 6)    /* in characters,
                                                         * excluding " [...]" */
#define BTRFSIC_GENERATION_UNKNOWN ((u64)-1)

/*
 * The definition of the bitmask fields for the print_mask.
 * They are specified with the mount option check_integrity_print_mask.
 */
#define BTRFSIC_PRINT_MASK_SUPERBLOCK_WRITE                     0x00000001
#define BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION         0x00000002
#define BTRFSIC_PRINT_MASK_TREE_AFTER_SB_WRITE                  0x00000004
#define BTRFSIC_PRINT_MASK_TREE_BEFORE_SB_WRITE                 0x00000008
#define BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH                        0x00000010
#define BTRFSIC_PRINT_MASK_END_IO_BIO_BH                        0x00000020
#define BTRFSIC_PRINT_MASK_VERBOSE                              0x00000040
#define BTRFSIC_PRINT_MASK_VERY_VERBOSE                         0x00000080
#define BTRFSIC_PRINT_MASK_INITIAL_TREE                         0x00000100
#define BTRFSIC_PRINT_MASK_INITIAL_ALL_TREES                    0x00000200
#define BTRFSIC_PRINT_MASK_INITIAL_DATABASE                     0x00000400
#define BTRFSIC_PRINT_MASK_NUM_COPIES                           0x00000800
#define BTRFSIC_PRINT_MASK_TREE_WITH_ALL_MIRRORS                0x00001000

struct btrfsic_dev_state;
struct btrfsic_state;

struct btrfsic_block {
        u32 magic_num;          /* only used for debug purposes */
        unsigned int is_metadata:1;     /* if it is meta-data, not data-data */
        unsigned int is_superblock:1;   /* if it is one of the superblocks */
        unsigned int is_iodone:1;       /* if is done by lower subsystem */
        unsigned int iodone_w_error:1;  /* error was indicated to endio */
        unsigned int never_written:1;   /* block was added because it was
                                         * referenced, not because it was
                                         * written */
        unsigned int mirror_num:2;      /* large enough to hold
                                         * BTRFS_SUPER_MIRROR_MAX */
        struct btrfsic_dev_state *dev_state;
        u64 dev_bytenr;         /* key, physical byte num on disk */
        u64 logical_bytenr;     /* logical byte num on disk */
        u64 generation;
        struct btrfs_disk_key disk_key; /* extra info to print in case of
                                         * issues, will not always be correct */
        struct list_head collision_resolving_node;      /* list node */
        struct list_head all_blocks_node;       /* list node */

        /* the following two lists contain block_link items */
        struct list_head ref_to_list;   /* list */
        struct list_head ref_from_list; /* list */
        struct btrfsic_block *next_in_same_bio;
        void *orig_bio_bh_private;
        union {
                bio_end_io_t *bio;
                bh_end_io_t *bh;
        } orig_bio_bh_end_io;
        int submit_bio_bh_rw;
        u64 flush_gen; /* only valid if !never_written */
};

/*
 * Elements of this type are allocated dynamically and required because
 * each block object can refer to and can be ref from multiple blocks.
 * The key to lookup them in the hashtable is the dev_bytenr of
 * the block ref to plus the one from the block refered from.
 * The fact that they are searchable via a hashtable and that a
 * ref_cnt is maintained is not required for the btrfs integrity
 * check algorithm itself, it is only used to make the output more
 * beautiful in case that an error is detected (an error is defined
 * as a write operation to a block while that block is still referenced).
 */
struct btrfsic_block_link {
        u32 magic_num;          /* only used for debug purposes */
        u32 ref_cnt;
        struct list_head node_ref_to;   /* list node */
        struct list_head node_ref_from; /* list node */
        struct list_head collision_resolving_node;      /* list node */
        struct btrfsic_block *block_ref_to;
        struct btrfsic_block *block_ref_from;
        u64 parent_generation;
};

struct btrfsic_dev_state {
        u32 magic_num;          /* only used for debug purposes */
        struct block_device *bdev;
        struct btrfsic_state *state;
        struct list_head collision_resolving_node;      /* list node */
        struct btrfsic_block dummy_block_for_bio_bh_flush;
        u64 last_flush_gen;
        char name[BDEVNAME_SIZE];
};

struct btrfsic_block_hashtable {
        struct list_head table[BTRFSIC_BLOCK_HASHTABLE_SIZE];
};

struct btrfsic_block_link_hashtable {
        struct list_head table[BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE];
};

struct btrfsic_dev_state_hashtable {
        struct list_head table[BTRFSIC_DEV2STATE_HASHTABLE_SIZE];
};

struct btrfsic_block_data_ctx {
        u64 start;              /* virtual bytenr */
        u64 dev_bytenr;         /* physical bytenr on device */
        u32 len;
        struct btrfsic_dev_state *dev;
        char **datav;
        struct page **pagev;
        void *mem_to_free;
};

/* This structure is used to implement recursion without occupying
 * any stack space, refer to btrfsic_process_metablock() */
struct btrfsic_stack_frame {
        u32 magic;
        u32 nr;
        int error;
        int i;
        int limit_nesting;
        int num_copies;
        int mirror_num;
        struct btrfsic_block *block;
        struct btrfsic_block_data_ctx *block_ctx;
        struct btrfsic_block *next_block;
        struct btrfsic_block_data_ctx next_block_ctx;
        struct btrfs_header *hdr;
        struct btrfsic_stack_frame *prev;
};

/* Some state per mounted filesystem */
struct btrfsic_state {
        u32 print_mask;
        int include_extent_data;
        int csum_size;
        struct list_head all_blocks_list;
        struct btrfsic_block_hashtable block_hashtable;
        struct btrfsic_block_link_hashtable block_link_hashtable;
        struct btrfs_root *root;
        u64 max_superblock_generation;
        struct btrfsic_block *latest_superblock;
        u32 metablock_size;
        u32 datablock_size;
};

static void btrfsic_block_init(struct btrfsic_block *b);
static struct btrfsic_block *btrfsic_block_alloc(void);
static void btrfsic_block_free(struct btrfsic_block *b);
static void btrfsic_block_link_init(struct btrfsic_block_link *n);
static struct btrfsic_block_link *btrfsic_block_link_alloc(void);
static void btrfsic_block_link_free(struct btrfsic_block_link *n);
static void btrfsic_dev_state_init(struct btrfsic_dev_state *ds);
static struct btrfsic_dev_state *btrfsic_dev_state_alloc(void);
static void btrfsic_dev_state_free(struct btrfsic_dev_state *ds);
static void btrfsic_block_hashtable_init(struct btrfsic_block_hashtable *h);
static void btrfsic_block_hashtable_add(struct btrfsic_block *b,
                                        struct btrfsic_block_hashtable *h);
static void btrfsic_block_hashtable_remove(struct btrfsic_block *b);
static struct btrfsic_block *btrfsic_block_hashtable_lookup(
                struct block_device *bdev,
                u64 dev_bytenr,
                struct btrfsic_block_hashtable *h);
static void btrfsic_block_link_hashtable_init(
                struct btrfsic_block_link_hashtable *h);
static void btrfsic_block_link_hashtable_add(
                struct btrfsic_block_link *l,
                struct btrfsic_block_link_hashtable *h);
static void btrfsic_block_link_hashtable_remove(struct btrfsic_block_link *l);
static struct btrfsic_block_link *btrfsic_block_link_hashtable_lookup(
                struct block_device *bdev_ref_to,
                u64 dev_bytenr_ref_to,
                struct block_device *bdev_ref_from,
                u64 dev_bytenr_ref_from,
                struct btrfsic_block_link_hashtable *h);
static void btrfsic_dev_state_hashtable_init(
                struct btrfsic_dev_state_hashtable *h);
static void btrfsic_dev_state_hashtable_add(
                struct btrfsic_dev_state *ds,
                struct btrfsic_dev_state_hashtable *h);
static void btrfsic_dev_state_hashtable_remove(struct btrfsic_dev_state *ds);
static struct btrfsic_dev_state *btrfsic_dev_state_hashtable_lookup(
                struct block_device *bdev,
                struct btrfsic_dev_state_hashtable *h);
static struct btrfsic_stack_frame *btrfsic_stack_frame_alloc(void);
static void btrfsic_stack_frame_free(struct btrfsic_stack_frame *sf);
static int btrfsic_process_superblock(struct btrfsic_state *state,
                                      struct btrfs_fs_devices *fs_devices);
static int btrfsic_process_metablock(struct btrfsic_state *state,
                                     struct btrfsic_block *block,
                                     struct btrfsic_block_data_ctx *block_ctx,
                                     int limit_nesting, int force_iodone_flag);
static void btrfsic_read_from_block_data(
        struct btrfsic_block_data_ctx *block_ctx,
        void *dst, u32 offset, size_t len);
static int btrfsic_create_link_to_next_block(
                struct btrfsic_state *state,
                struct btrfsic_block *block,
                struct btrfsic_block_data_ctx
                *block_ctx, u64 next_bytenr,
                int limit_nesting,
                struct btrfsic_block_data_ctx *next_block_ctx,
                struct btrfsic_block **next_blockp,
                int force_iodone_flag,
                int *num_copiesp, int *mirror_nump,
                struct btrfs_disk_key *disk_key,
                u64 parent_generation);
static int btrfsic_handle_extent_data(struct btrfsic_state *state,
                                      struct btrfsic_block *block,
                                      struct btrfsic_block_data_ctx *block_ctx,
                                      u32 item_offset, int force_iodone_flag);
static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
                             struct btrfsic_block_data_ctx *block_ctx_out,
                             int mirror_num);
static int btrfsic_map_superblock(struct btrfsic_state *state, u64 bytenr,
                                  u32 len, struct block_device *bdev,
                                  struct btrfsic_block_data_ctx *block_ctx_out);
static void btrfsic_release_block_ctx(struct btrfsic_block_data_ctx *block_ctx);
static int btrfsic_read_block(struct btrfsic_state *state,
                              struct btrfsic_block_data_ctx *block_ctx);
static void btrfsic_dump_database(struct btrfsic_state *state);
static void btrfsic_complete_bio_end_io(struct bio *bio, int err);
static int btrfsic_test_for_metadata(struct btrfsic_state *state,
                                     char **datav, unsigned int num_pages);
static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
                                          u64 dev_bytenr, char **mapped_datav,
                                          unsigned int num_pages,
                                          struct bio *bio, int *bio_is_patched,
                                          struct buffer_head *bh,
                                          int submit_bio_bh_rw);
static int btrfsic_process_written_superblock(
                struct btrfsic_state *state,
                struct btrfsic_block *const block,
                struct btrfs_super_block *const super_hdr);
static void btrfsic_bio_end_io(struct bio *bp, int bio_error_status);
static void btrfsic_bh_end_io(struct buffer_head *bh, int uptodate);
static int btrfsic_is_block_ref_by_superblock(const struct btrfsic_state *state,
                                              const struct btrfsic_block *block,
                                              int recursion_level);
static int btrfsic_check_all_ref_blocks(struct btrfsic_state *state,
                                        struct btrfsic_block *const block,
                                        int recursion_level);
static void btrfsic_print_add_link(const struct btrfsic_state *state,
                                   const struct btrfsic_block_link *l);
static void btrfsic_print_rem_link(const struct btrfsic_state *state,
                                   const struct btrfsic_block_link *l);
static char btrfsic_get_block_type(const struct btrfsic_state *state,
                                   const struct btrfsic_block *block);
static void btrfsic_dump_tree(const struct btrfsic_state *state);
static void btrfsic_dump_tree_sub(const struct btrfsic_state *state,
                                  const struct btrfsic_block *block,
                                  int indent_level);
static struct btrfsic_block_link *btrfsic_block_link_lookup_or_add(
                struct btrfsic_state *state,
                struct btrfsic_block_data_ctx *next_block_ctx,
                struct btrfsic_block *next_block,
                struct btrfsic_block *from_block,
                u64 parent_generation);
static struct btrfsic_block *btrfsic_block_lookup_or_add(
                struct btrfsic_state *state,
                struct btrfsic_block_data_ctx *block_ctx,
                const char *additional_string,
                int is_metadata,
                int is_iodone,
                int never_written,
                int mirror_num,
                int *was_created);
static int btrfsic_process_superblock_dev_mirror(
                struct btrfsic_state *state,
                struct btrfsic_dev_state *dev_state,
                struct btrfs_device *device,
                int superblock_mirror_num,
                struct btrfsic_dev_state **selected_dev_state,
                struct btrfs_super_block *selected_super);
static struct btrfsic_dev_state *btrfsic_dev_state_lookup(
                struct block_device *bdev);
static void btrfsic_cmp_log_and_dev_bytenr(struct btrfsic_state *state,
                                           u64 bytenr,
                                           struct btrfsic_dev_state *dev_state,
                                           u64 dev_bytenr);

static struct mutex btrfsic_mutex;
static int btrfsic_is_initialized;
static struct btrfsic_dev_state_hashtable btrfsic_dev_state_hashtable;


static void btrfsic_block_init(struct btrfsic_block *b)
{
        b->magic_num = BTRFSIC_BLOCK_MAGIC_NUMBER;
        b->dev_state = NULL;
        b->dev_bytenr = 0;
        b->logical_bytenr = 0;
        b->generation = BTRFSIC_GENERATION_UNKNOWN;
        b->disk_key.objectid = 0;
        b->disk_key.type = 0;
        b->disk_key.offset = 0;
        b->is_metadata = 0;
        b->is_superblock = 0;
        b->is_iodone = 0;
        b->iodone_w_error = 0;
        b->never_written = 0;
        b->mirror_num = 0;
        b->next_in_same_bio = NULL;
        b->orig_bio_bh_private = NULL;
        b->orig_bio_bh_end_io.bio = NULL;
        INIT_LIST_HEAD(&b->collision_resolving_node);
        INIT_LIST_HEAD(&b->all_blocks_node);
        INIT_LIST_HEAD(&b->ref_to_list);
        INIT_LIST_HEAD(&b->ref_from_list);
        b->submit_bio_bh_rw = 0;
        b->flush_gen = 0;
}

static struct btrfsic_block *btrfsic_block_alloc(void)
{
        struct btrfsic_block *b;

        b = kzalloc(sizeof(*b), GFP_NOFS);
        if (NULL != b)
                btrfsic_block_init(b);

        return b;
}

static void btrfsic_block_free(struct btrfsic_block *b)
{
        BUG_ON(!(NULL == b || BTRFSIC_BLOCK_MAGIC_NUMBER == b->magic_num));
        kfree(b);
}

static void btrfsic_block_link_init(struct btrfsic_block_link *l)
{
        l->magic_num = BTRFSIC_BLOCK_LINK_MAGIC_NUMBER;
        l->ref_cnt = 1;
        INIT_LIST_HEAD(&l->node_ref_to);
        INIT_LIST_HEAD(&l->node_ref_from);
        INIT_LIST_HEAD(&l->collision_resolving_node);
        l->block_ref_to = NULL;
        l->block_ref_from = NULL;
}

static struct btrfsic_block_link *btrfsic_block_link_alloc(void)
{
        struct btrfsic_block_link *l;

        l = kzalloc(sizeof(*l), GFP_NOFS);
        if (NULL != l)
                btrfsic_block_link_init(l);

        return l;
}

static void btrfsic_block_link_free(struct btrfsic_block_link *l)
{
        BUG_ON(!(NULL == l || BTRFSIC_BLOCK_LINK_MAGIC_NUMBER == l->magic_num));
        kfree(l);
}

static void btrfsic_dev_state_init(struct btrfsic_dev_state *ds)
{
        ds->magic_num = BTRFSIC_DEV2STATE_MAGIC_NUMBER;
        ds->bdev = NULL;
        ds->state = NULL;
        ds->name[0] = '\0';
        INIT_LIST_HEAD(&ds->collision_resolving_node);
        ds->last_flush_gen = 0;
        btrfsic_block_init(&ds->dummy_block_for_bio_bh_flush);
        ds->dummy_block_for_bio_bh_flush.is_iodone = 1;
        ds->dummy_block_for_bio_bh_flush.dev_state = ds;
}

static struct btrfsic_dev_state *btrfsic_dev_state_alloc(void)
{
        struct btrfsic_dev_state *ds;

        ds = kzalloc(sizeof(*ds), GFP_NOFS);
        if (NULL != ds)
                btrfsic_dev_state_init(ds);

        return ds;
}

static void btrfsic_dev_state_free(struct btrfsic_dev_state *ds)
{
        BUG_ON(!(NULL == ds ||
                 BTRFSIC_DEV2STATE_MAGIC_NUMBER == ds->magic_num));
        kfree(ds);
}

static void btrfsic_block_hashtable_init(struct btrfsic_block_hashtable *h)
{
        int i;

        for (i = 0; i < BTRFSIC_BLOCK_HASHTABLE_SIZE; i++)
                INIT_LIST_HEAD(h->table + i);
}

static void btrfsic_block_hashtable_add(struct btrfsic_block *b,
                                        struct btrfsic_block_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)(b->dev_bytenr >> 16)) ^
             ((unsigned int)((uintptr_t)b->dev_state->bdev))) &
             (BTRFSIC_BLOCK_HASHTABLE_SIZE - 1);

        list_add(&b->collision_resolving_node, h->table + hashval);
}

static void btrfsic_block_hashtable_remove(struct btrfsic_block *b)
{
        list_del(&b->collision_resolving_node);
}

static struct btrfsic_block *btrfsic_block_hashtable_lookup(
                struct block_device *bdev,
                u64 dev_bytenr,
                struct btrfsic_block_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)(dev_bytenr >> 16)) ^
             ((unsigned int)((uintptr_t)bdev))) &
             (BTRFSIC_BLOCK_HASHTABLE_SIZE - 1);
        struct list_head *elem;

        list_for_each(elem, h->table + hashval) {
                struct btrfsic_block *const b =
                    list_entry(elem, struct btrfsic_block,
                               collision_resolving_node);

                if (b->dev_state->bdev == bdev && b->dev_bytenr == dev_bytenr)
                        return b;
        }

        return NULL;
}

static void btrfsic_block_link_hashtable_init(
                struct btrfsic_block_link_hashtable *h)
{
        int i;

        for (i = 0; i < BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE; i++)
                INIT_LIST_HEAD(h->table + i);
}

static void btrfsic_block_link_hashtable_add(
                struct btrfsic_block_link *l,
                struct btrfsic_block_link_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)(l->block_ref_to->dev_bytenr >> 16)) ^
             ((unsigned int)(l->block_ref_from->dev_bytenr >> 16)) ^
             ((unsigned int)((uintptr_t)l->block_ref_to->dev_state->bdev)) ^
             ((unsigned int)((uintptr_t)l->block_ref_from->dev_state->bdev)))
             & (BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE - 1);

        BUG_ON(NULL == l->block_ref_to);
        BUG_ON(NULL == l->block_ref_from);
        list_add(&l->collision_resolving_node, h->table + hashval);
}

static void btrfsic_block_link_hashtable_remove(struct btrfsic_block_link *l)
{
        list_del(&l->collision_resolving_node);
}

static struct btrfsic_block_link *btrfsic_block_link_hashtable_lookup(
                struct block_device *bdev_ref_to,
                u64 dev_bytenr_ref_to,
                struct block_device *bdev_ref_from,
                u64 dev_bytenr_ref_from,
                struct btrfsic_block_link_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)(dev_bytenr_ref_to >> 16)) ^
             ((unsigned int)(dev_bytenr_ref_from >> 16)) ^
             ((unsigned int)((uintptr_t)bdev_ref_to)) ^
             ((unsigned int)((uintptr_t)bdev_ref_from))) &
             (BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE - 1);
        struct list_head *elem;

        list_for_each(elem, h->table + hashval) {
                struct btrfsic_block_link *const l =
                    list_entry(elem, struct btrfsic_block_link,
                               collision_resolving_node);

                BUG_ON(NULL == l->block_ref_to);
                BUG_ON(NULL == l->block_ref_from);
                if (l->block_ref_to->dev_state->bdev == bdev_ref_to &&
                    l->block_ref_to->dev_bytenr == dev_bytenr_ref_to &&
                    l->block_ref_from->dev_state->bdev == bdev_ref_from &&
                    l->block_ref_from->dev_bytenr == dev_bytenr_ref_from)
                        return l;
        }

        return NULL;
}

static void btrfsic_dev_state_hashtable_init(
                struct btrfsic_dev_state_hashtable *h)
{
        int i;

        for (i = 0; i < BTRFSIC_DEV2STATE_HASHTABLE_SIZE; i++)
                INIT_LIST_HEAD(h->table + i);
}

static void btrfsic_dev_state_hashtable_add(
                struct btrfsic_dev_state *ds,
                struct btrfsic_dev_state_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)((uintptr_t)ds->bdev)) &
             (BTRFSIC_DEV2STATE_HASHTABLE_SIZE - 1));

        list_add(&ds->collision_resolving_node, h->table + hashval);
}

static void btrfsic_dev_state_hashtable_remove(struct btrfsic_dev_state *ds)
{
        list_del(&ds->collision_resolving_node);
}

static struct btrfsic_dev_state *btrfsic_dev_state_hashtable_lookup(
                struct block_device *bdev,
                struct btrfsic_dev_state_hashtable *h)
{
        const unsigned int hashval =
            (((unsigned int)((uintptr_t)bdev)) &
             (BTRFSIC_DEV2STATE_HASHTABLE_SIZE - 1));
        struct list_head *elem;

        list_for_each(elem, h->table + hashval) {
                struct btrfsic_dev_state *const ds =
                    list_entry(elem, struct btrfsic_dev_state,
                               collision_resolving_node);

                if (ds->bdev == bdev)
                        return ds;
        }

        return NULL;
}

static int btrfsic_process_superblock(struct btrfsic_state *state,
                                      struct btrfs_fs_devices *fs_devices)
{
        int ret = 0;
        struct btrfs_super_block *selected_super;
        struct list_head *dev_head = &fs_devices->devices;
        struct btrfs_device *device;
        struct btrfsic_dev_state *selected_dev_state = NULL;
        int pass;

        BUG_ON(NULL == state);
        selected_super = kzalloc(sizeof(*selected_super), GFP_NOFS);
        if (NULL == selected_super) {
                printk(KERN_INFO "btrfsic: error, kmalloc failed!\n");
                return -1;
        }

        list_for_each_entry(device, dev_head, dev_list) {
                int i;
                struct btrfsic_dev_state *dev_state;

                if (!device->bdev || !device->name)
                        continue;

                dev_state = btrfsic_dev_state_lookup(device->bdev);
                BUG_ON(NULL == dev_state);
                for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                        ret = btrfsic_process_superblock_dev_mirror(
                                        state, dev_state, device, i,
                                        &selected_dev_state, selected_super);
                        if (0 != ret && 0 == i) {
                                kfree(selected_super);
                                return ret;
                        }
                }
        }

        if (NULL == state->latest_superblock) {
                printk(KERN_INFO "btrfsic: no superblock found!\n");
                kfree(selected_super);
                return -1;
        }

        state->csum_size = btrfs_super_csum_size(selected_super);

        for (pass = 0; pass < 3; pass++) {
                int num_copies;
                int mirror_num;
                u64 next_bytenr;

                switch (pass) {
                case 0:
                        next_bytenr = btrfs_super_root(selected_super);
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "root@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                case 1:
                        next_bytenr = btrfs_super_chunk_root(selected_super);
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "chunk@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                case 2:
                        next_bytenr = btrfs_super_log_root(selected_super);
                        if (0 == next_bytenr)
                                continue;
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "log@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                }

                num_copies =
                    btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                     next_bytenr, state->metablock_size);
                if (state->print_mask & BTRFSIC_PRINT_MASK_NUM_COPIES)
                        printk(KERN_INFO "num_copies(log_bytenr=%llu) = %d\n",
                               (unsigned long long)next_bytenr, num_copies);

                for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                        struct btrfsic_block *next_block;
                        struct btrfsic_block_data_ctx tmp_next_block_ctx;
                        struct btrfsic_block_link *l;

                        ret = btrfsic_map_block(state, next_bytenr,
                                                state->metablock_size,
                                                &tmp_next_block_ctx,
                                                mirror_num);
                        if (ret) {
                                printk(KERN_INFO "btrfsic:"
                                       " btrfsic_map_block(root @%llu,"
                                       " mirror %d) failed!\n",
                                       (unsigned long long)next_bytenr,
                                       mirror_num);
                                kfree(selected_super);
                                return -1;
                        }

                        next_block = btrfsic_block_hashtable_lookup(
                                        tmp_next_block_ctx.dev->bdev,
                                        tmp_next_block_ctx.dev_bytenr,
                                        &state->block_hashtable);
                        BUG_ON(NULL == next_block);

                        l = btrfsic_block_link_hashtable_lookup(
                                        tmp_next_block_ctx.dev->bdev,
                                        tmp_next_block_ctx.dev_bytenr,
                                        state->latest_superblock->dev_state->
                                        bdev,
                                        state->latest_superblock->dev_bytenr,
                                        &state->block_link_hashtable);
                        BUG_ON(NULL == l);

                        ret = btrfsic_read_block(state, &tmp_next_block_ctx);
                        if (ret < (int)PAGE_CACHE_SIZE) {
                                printk(KERN_INFO
                                       "btrfsic: read @logical %llu failed!\n",
                                       (unsigned long long)
                                       tmp_next_block_ctx.start);
                                btrfsic_release_block_ctx(&tmp_next_block_ctx);
                                kfree(selected_super);
                                return -1;
                        }

                        ret = btrfsic_process_metablock(state,
                                                        next_block,
                                                        &tmp_next_block_ctx,
                                                        BTRFS_MAX_LEVEL + 3, 1);
                        btrfsic_release_block_ctx(&tmp_next_block_ctx);
                }
        }

        kfree(selected_super);
        return ret;
}

static int btrfsic_process_superblock_dev_mirror(
                struct btrfsic_state *state,
                struct btrfsic_dev_state *dev_state,
                struct btrfs_device *device,
                int superblock_mirror_num,
                struct btrfsic_dev_state **selected_dev_state,
                struct btrfs_super_block *selected_super)
{
        struct btrfs_super_block *super_tmp;
        u64 dev_bytenr;
        struct buffer_head *bh;
        struct btrfsic_block *superblock_tmp;
        int pass;
        struct block_device *const superblock_bdev = device->bdev;

        /* super block bytenr is always the unmapped device bytenr */
        dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
        if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->total_bytes)
                return -1;
        bh = __bread(superblock_bdev, dev_bytenr / 4096,
                     BTRFS_SUPER_INFO_SIZE);
        if (NULL == bh)
                return -1;
        super_tmp = (struct btrfs_super_block *)
            (bh->b_data + (dev_bytenr & 4095));

        if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
            strncmp((char *)(&(super_tmp->magic)), BTRFS_MAGIC,
                    sizeof(super_tmp->magic)) ||
            memcmp(device->uuid, super_tmp->dev_item.uuid, BTRFS_UUID_SIZE) ||
            btrfs_super_nodesize(super_tmp) != state->metablock_size ||
            btrfs_super_leafsize(super_tmp) != state->metablock_size ||
            btrfs_super_sectorsize(super_tmp) != state->datablock_size) {
                brelse(bh);
                return 0;
        }

        superblock_tmp =
            btrfsic_block_hashtable_lookup(superblock_bdev,
                                           dev_bytenr,
                                           &state->block_hashtable);
        if (NULL == superblock_tmp) {
                superblock_tmp = btrfsic_block_alloc();
                if (NULL == superblock_tmp) {
                        printk(KERN_INFO "btrfsic: error, kmalloc failed!\n");
                        brelse(bh);
                        return -1;
                }
                /* for superblock, only the dev_bytenr makes sense */
                superblock_tmp->dev_bytenr = dev_bytenr;
                superblock_tmp->dev_state = dev_state;
                superblock_tmp->logical_bytenr = dev_bytenr;
                superblock_tmp->generation = btrfs_super_generation(super_tmp);
                superblock_tmp->is_metadata = 1;
                superblock_tmp->is_superblock = 1;
                superblock_tmp->is_iodone = 1;
                superblock_tmp->never_written = 0;
                superblock_tmp->mirror_num = 1 + superblock_mirror_num;
                if (state->print_mask & BTRFSIC_PRINT_MASK_SUPERBLOCK_WRITE)
                        printk_in_rcu(KERN_INFO "New initial S-block (bdev %p, %s)"
                                     " @%llu (%s/%llu/%d)\n",
                                     superblock_bdev,
                                     rcu_str_deref(device->name),
                                     (unsigned long long)dev_bytenr,
                                     dev_state->name,
                                     (unsigned long long)dev_bytenr,
                                     superblock_mirror_num);
                list_add(&superblock_tmp->all_blocks_node,
                         &state->all_blocks_list);
                btrfsic_block_hashtable_add(superblock_tmp,
                                            &state->block_hashtable);
        }

        /* select the one with the highest generation field */
        if (btrfs_super_generation(super_tmp) >
            state->max_superblock_generation ||
            0 == state->max_superblock_generation) {
                memcpy(selected_super, super_tmp, sizeof(*selected_super));
                *selected_dev_state = dev_state;
                state->max_superblock_generation =
                    btrfs_super_generation(super_tmp);
                state->latest_superblock = superblock_tmp;
        }

        for (pass = 0; pass < 3; pass++) {
                u64 next_bytenr;
                int num_copies;
                int mirror_num;
                const char *additional_string = NULL;
                struct btrfs_disk_key tmp_disk_key;

                tmp_disk_key.type = BTRFS_ROOT_ITEM_KEY;
                tmp_disk_key.offset = 0;
                switch (pass) {
                case 0:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_ROOT_TREE_OBJECTID);
                        additional_string = "initial root ";
                        next_bytenr = btrfs_super_root(super_tmp);
                        break;
                case 1:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_CHUNK_TREE_OBJECTID);
                        additional_string = "initial chunk ";
                        next_bytenr = btrfs_super_chunk_root(super_tmp);
                        break;
                case 2:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_TREE_LOG_OBJECTID);
                        additional_string = "initial log ";
                        next_bytenr = btrfs_super_log_root(super_tmp);
                        if (0 == next_bytenr)
                                continue;
                        break;
                }

                num_copies =
                    btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                     next_bytenr, state->metablock_size);
                if (state->print_mask & BTRFSIC_PRINT_MASK_NUM_COPIES)
                        printk(KERN_INFO "num_copies(log_bytenr=%llu) = %d\n",
                               (unsigned long long)next_bytenr, num_copies);
                for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                        struct btrfsic_block *next_block;
                        struct btrfsic_block_data_ctx tmp_next_block_ctx;
                        struct btrfsic_block_link *l;

                        if (btrfsic_map_block(state, next_bytenr,
                                              state->metablock_size,
                                              &tmp_next_block_ctx,
                                              mirror_num)) {
                                printk(KERN_INFO "btrfsic: btrfsic_map_block("
                                       "bytenr @%llu, mirror %d) failed!\n",
                                       (unsigned long long)next_bytenr,
                                       mirror_num);
                                brelse(bh);
                                return -1;
                        }

                        next_block = btrfsic_block_lookup_or_add(
                                        state, &tmp_next_block_ctx,
                                        additional_string, 1, 1, 0,
                                        mirror_num, NULL);
                        if (NULL == next_block) {
                                btrfsic_release_block_ctx(&tmp_next_block_ctx);
                                brelse(bh);
                                return -1;
                        }

                        next_block->disk_key = tmp_disk_key;
                        next_block->generation = BTRFSIC_GENERATION_UNKNOWN;
                        l = btrfsic_block_link_lookup_or_add(
                                        state, &tmp_next_block_ctx,
                                        next_block, superblock_tmp,
                                        BTRFSIC_GENERATION_UNKNOWN);
                        btrfsic_release_block_ctx(&tmp_next_block_ctx);
                        if (NULL == l) {
                                brelse(bh);
                                return -1;
                        }
                }
        }
        if (state->print_mask & BTRFSIC_PRINT_MASK_INITIAL_ALL_TREES)
                btrfsic_dump_tree_sub(state, superblock_tmp, 0);

        brelse(bh);
        return 0;
}

static struct btrfsic_stack_frame *btrfsic_stack_frame_alloc(void)
{
        struct btrfsic_stack_frame *sf;

        sf = kzalloc(sizeof(*sf), GFP_NOFS);
        if (NULL == sf)
                printk(KERN_INFO "btrfsic: alloc memory failed!\n");
        else
                sf->magic = BTRFSIC_BLOCK_STACK_FRAME_MAGIC_NUMBER;
        return sf;
}

static void btrfsic_stack_frame_free(struct btrfsic_stack_frame *sf)
{
        BUG_ON(!(NULL == sf ||
                 BTRFSIC_BLOCK_STACK_FRAME_MAGIC_NUMBER == sf->magic));
        kfree(sf);
}

static int btrfsic_process_metablock(
                struct btrfsic_state *state,
                struct btrfsic_block *const first_block,
                struct btrfsic_block_data_ctx *const first_block_ctx,
                int first_limit_nesting, int force_iodone_flag)
{
        struct btrfsic_stack_frame initial_stack_frame = { 0 };
        struct btrfsic_stack_frame *sf;
        struct btrfsic_stack_frame *next_stack;
        struct btrfs_header *const first_hdr =
                (struct btrfs_header *)first_block_ctx->datav[0];

        BUG_ON(!first_hdr);
        sf = &initial_stack_frame;
        sf->error = 0;
        sf->i = -1;
        sf->limit_nesting = first_limit_nesting;
        sf->block = first_block;
        sf->block_ctx = first_block_ctx;
        sf->next_block = NULL;
        sf->hdr = first_hdr;
        sf->prev = NULL;

continue_with_new_stack_frame:
        sf->block->generation = le64_to_cpu(sf->hdr->generation);

        if (0 == sf->hdr->level) {
                struct btrfs_leaf *const leafhdr =
                    (struct btrfs_leaf *)sf->hdr;

                if (-1 == sf->i) {
                        sf->nr = le32_to_cpu(leafhdr->header.nritems);

                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO
                                       "leaf %llu items %d generation %llu"
                                       " owner %llu\n",
                                       (unsigned long long)
                                       sf->block_ctx->start,
                                       sf->nr,
                                       (unsigned long long)
                                       le64_to_cpu(leafhdr->header.generation),
                                       (unsigned long long)
                                       le64_to_cpu(leafhdr->header.owner));
                }

continue_with_current_leaf_stack_frame:
                if (0 == sf->num_copies || sf->mirror_num > sf->num_copies) {
                        sf->i++;
                        sf->num_copies = 0;
                }

                if (sf->i < sf->nr) {
                        struct btrfs_item disk_item;
                        u32 disk_item_offset =
                                (uintptr_t)(leafhdr->items + sf->i) -
                                (uintptr_t)leafhdr;
                        struct btrfs_disk_key *disk_key;
                        u8 type;
                        u32 item_offset;
                        u32 item_size;

                        if (disk_item_offset + sizeof(struct btrfs_item) >
                            sf->block_ctx->len) {
leaf_item_out_of_bounce_error:
                                printk(KERN_INFO
                                       "btrfsic: leaf item out of bounce at logical %llu, dev %s\n",
                                       sf->block_ctx->start,
                                       sf->block_ctx->dev->name);
                                goto one_stack_frame_backwards;
                        }
                        btrfsic_read_from_block_data(sf->block_ctx,
                                                     &disk_item,
                                                     disk_item_offset,
                                                     sizeof(struct btrfs_item));
                        item_offset = le32_to_cpu(disk_item.offset);
                        item_size = le32_to_cpu(disk_item.size);
                        disk_key = &disk_item.key;
                        type = disk_key->type;

                        if (BTRFS_ROOT_ITEM_KEY == type) {
                                struct btrfs_root_item root_item;
                                u32 root_item_offset;
                                u64 next_bytenr;

                                root_item_offset = item_offset +
                                        offsetof(struct btrfs_leaf, items);
                                if (root_item_offset + item_size >
                                    sf->block_ctx->len)
                                        goto leaf_item_out_of_bounce_error;
                                btrfsic_read_from_block_data(
                                        sf->block_ctx, &root_item,
                                        root_item_offset,
                                        item_size);
                                next_bytenr = le64_to_cpu(root_item.bytenr);

                                sf->error =
                                    btrfsic_create_link_to_next_block(
                                                state,
                                                sf->block,
                                                sf->block_ctx,
                                                next_bytenr,
                                                sf->limit_nesting,
                                                &sf->next_block_ctx,
                                                &sf->next_block,
                                                force_iodone_flag,
                                                &sf->num_copies,
                                                &sf->mirror_num,
                                                disk_key,
                                                le64_to_cpu(root_item.
                                                generation));
                                if (sf->error)
                                        goto one_stack_frame_backwards;

                                if (NULL != sf->next_block) {
                                        struct btrfs_header *const next_hdr =
                                            (struct btrfs_header *)
                                            sf->next_block_ctx.datav[0];

                                        next_stack =
                                            btrfsic_stack_frame_alloc();
                                        if (NULL == next_stack) {
                                                btrfsic_release_block_ctx(
                                                                &sf->
                                                                next_block_ctx);
                                                goto one_stack_frame_backwards;
                                        }

                                        next_stack->i = -1;
                                        next_stack->block = sf->next_block;
                                        next_stack->block_ctx =
                                            &sf->next_block_ctx;
                                        next_stack->next_block = NULL;
                                        next_stack->hdr = next_hdr;
                                        next_stack->limit_nesting =
                                            sf->limit_nesting - 1;
                                        next_stack->prev = sf;
                                        sf = next_stack;
                                        goto continue_with_new_stack_frame;
                                }
                        } else if (BTRFS_EXTENT_DATA_KEY == type &&
                                   state->include_extent_data) {
                                sf->error = btrfsic_handle_extent_data(
                                                state,
                                                sf->block,
                                                sf->block_ctx,
                                                item_offset,
                                                force_iodone_flag);
                                if (sf->error)
                                        goto one_stack_frame_backwards;
                        }

                        goto continue_with_current_leaf_stack_frame;
                }
        } else {
                struct btrfs_node *const nodehdr = (struct btrfs_node *)sf->hdr;

                if (-1 == sf->i) {
                        sf->nr = le32_to_cpu(nodehdr->header.nritems);

                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO "node %llu level %d items %d"
                                       " generation %llu owner %llu\n",
                                       (unsigned long long)
                                       sf->block_ctx->start,
                                       nodehdr->header.level, sf->nr,
                                       (unsigned long long)
                                       le64_to_cpu(nodehdr->header.generation),
                                       (unsigned long long)
                                       le64_to_cpu(nodehdr->header.owner));
                }

continue_with_current_node_stack_frame:
                if (0 == sf->num_copies || sf->mirror_num > sf->num_copies) {
                        sf->i++;
                        sf->num_copies = 0;
                }

                if (sf->i < sf->nr) {
                        struct btrfs_key_ptr key_ptr;
                        u32 key_ptr_offset;
                        u64 next_bytenr;

                        key_ptr_offset = (uintptr_t)(nodehdr->ptrs + sf->i) -
                                          (uintptr_t)nodehdr;
                        if (key_ptr_offset + sizeof(struct btrfs_key_ptr) >
                            sf->block_ctx->len) {
                                printk(KERN_INFO
                                       "btrfsic: node item out of bounce at logical %llu, dev %s\n",
                                       sf->block_ctx->start,
                                       sf->block_ctx->dev->name);
                                goto one_stack_frame_backwards;
                        }
                        btrfsic_read_from_block_data(
                                sf->block_ctx, &key_ptr, key_ptr_offset,
                                sizeof(struct btrfs_key_ptr));
                        next_bytenr = le64_to_cpu(key_ptr.blockptr);

                        sf->error = btrfsic_create_link_to_next_block(
                                        state,
                                        sf->block,
                                        sf->block_ctx,
                                        next_bytenr,
                                        sf->limit_nesting,
                                        &sf->next_block_ctx,
                                        &sf->next_block,
                                        force_iodone_flag,
                                        &sf->num_copies,
                                        &sf->mirror_num,
                                        &key_ptr.key,
                                        le64_to_cpu(key_ptr.generation));
                        if (sf->error)
                                goto one_stack_frame_backwards;

                        if (NULL != sf->next_block) {
                                struct btrfs_header *const next_hdr =
                                    (struct btrfs_header *)
                                    sf->next_block_ctx.datav[0];

                                next_stack = btrfsic_stack_frame_alloc();
                                if (NULL == next_stack)
                                        goto one_stack_frame_backwards;

                                next_stack->i = -1;
                                next_stack->block = sf->next_block;
                                next_stack->block_ctx = &sf->next_block_ctx;
                                next_stack->next_block = NULL;
                                next_stack->hdr = next_hdr;
                                next_stack->limit_nesting =
                                    sf->limit_nesting - 1;
                                next_stack->prev = sf;
                                sf = next_stack;
                                goto continue_with_new_stack_frame;
                        }

                        goto continue_with_current_node_stack_frame;
                }
        }

one_stack_frame_backwards:
        if (NULL != sf->prev) {
                struct btrfsic_stack_frame *const prev = sf->prev;

                /* the one for the initial block is freed in the caller */
                btrfsic_release_block_ctx(sf->block_ctx);

                if (sf->error) {
                        prev->error = sf->error;
                        btrfsic_stack_frame_free(sf);
                        sf = prev;
                        goto one_stack_frame_backwards;
                }

                btrfsic_stack_frame_free(sf);
                sf = prev;
                goto continue_with_new_stack_frame;
        } else {
                BUG_ON(&initial_stack_frame != sf);
        }

        return sf->error;
}

static void btrfsic_read_from_block_data(
        struct btrfsic_block_data_ctx *block_ctx,
        void *dstv, u32 offset, size_t len)
{
        size_t cur;
        size_t offset_in_page;
        char *kaddr;
        char *dst = (char *)dstv;
        size_t start_offset = block_ctx->start & ((u64)PAGE_CACHE_SIZE - 1);
        unsigned long i = (start_offset + offset) >> PAGE_CACHE_SHIFT;

        WARN_ON(offset + len > block_ctx->len);
        offset_in_page = (start_offset + offset) &
                         ((unsigned long)PAGE_CACHE_SIZE - 1);

        while (len > 0) {
                cur = min(len, ((size_t)PAGE_CACHE_SIZE - offset_in_page));
                BUG_ON(i >= (block_ctx->len + PAGE_CACHE_SIZE - 1) >>
                            PAGE_CACHE_SHIFT);
                kaddr = block_ctx->datav[i];
                memcpy(dst, kaddr + offset_in_page, cur);

                dst += cur;
                len -= cur;
                offset_in_page = 0;
                i++;
        }
}

static int btrfsic_create_link_to_next_block(
                struct btrfsic_state *state,
                struct btrfsic_block *block,
                struct btrfsic_block_data_ctx *block_ctx,
                u64 next_bytenr,
                int limit_nesting,
                struct btrfsic_block_data_ctx *next_block_ctx,
                struct btrfsic_block **next_blockp,
                int force_iodone_flag,
                int *num_copiesp, int *mirror_nump,
                struct btrfs_disk_key *disk_key,
                u64 parent_generation)
{
        struct btrfsic_block *next_block = NULL;
        int ret;
        struct btrfsic_block_link *l;
        int did_alloc_block_link;
        int block_was_created;

        *next_blockp = NULL;
        if (0 == *num_copiesp) {
                *num_copiesp =
                    btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                     next_bytenr, state->metablock_size);
                if (state->print_mask & BTRFSIC_PRINT_MASK_NUM_COPIES)
                        printk(KERN_INFO "num_copies(log_bytenr=%llu) = %d\n",
                               (unsigned long long)next_bytenr, *num_copiesp);
                *mirror_nump = 1;
        }

        if (*mirror_nump > *num_copiesp)
                return 0;

        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                printk(KERN_INFO
                       "btrfsic_create_link_to_next_block(mirror_num=%d)\n",
                       *mirror_nump);
        ret = btrfsic_map_block(state, next_bytenr,
                                state->metablock_size,
                                next_block_ctx, *mirror_nump);
        if (ret) {
                printk(KERN_INFO
                       "btrfsic: btrfsic_map_block(@%llu, mirror=%d) failed!\n",
                       (unsigned long long)next_bytenr, *mirror_nump);
                btrfsic_release_block_ctx(next_block_ctx);
                *next_blockp = NULL;
                return -1;
        }

        next_block = btrfsic_block_lookup_or_add(state,
                                                 next_block_ctx, "referenced ",
                                                 1, force_iodone_flag,
                                                 !force_iodone_flag,
                                                 *mirror_nump,
                                                 &block_was_created);
        if (NULL == next_block) {
                btrfsic_release_block_ctx(next_block_ctx);
                *next_blockp = NULL;
                return -1;
        }
        if (block_was_created) {
                l = NULL;
                next_block->generation = BTRFSIC_GENERATION_UNKNOWN;
        } else {
                if (next_block->logical_bytenr != next_bytenr &&
                    !(!next_block->is_metadata &&
                      0 == next_block->logical_bytenr)) {
                        printk(KERN_INFO
                               "Referenced block @%llu (%s/%llu/%d)"
                               " found in hash table, %c,"
                               " bytenr mismatch (!= stored %llu).\n",
                               (unsigned long long)next_bytenr,
                               next_block_ctx->dev->name,
                               (unsigned long long)next_block_ctx->dev_bytenr,
                               *mirror_nump,
                               btrfsic_get_block_type(state, next_block),
                               (unsigned long long)next_block->logical_bytenr);
                } else if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "Referenced block @%llu (%s/%llu/%d)"
                               " found in hash table, %c.\n",
                               (unsigned long long)next_bytenr,
                               next_block_ctx->dev->name,
                               (unsigned long long)next_block_ctx->dev_bytenr,
                               *mirror_nump,
                               btrfsic_get_block_type(state, next_block));
                next_block->logical_bytenr = next_bytenr;

                next_block->mirror_num = *mirror_nump;
                l = btrfsic_block_link_hashtable_lookup(
                                next_block_ctx->dev->bdev,
                                next_block_ctx->dev_bytenr,
                                block_ctx->dev->bdev,
                                block_ctx->dev_bytenr,
                                &state->block_link_hashtable);
        }

        next_block->disk_key = *disk_key;
        if (NULL == l) {
                l = btrfsic_block_link_alloc();
                if (NULL == l) {
                        printk(KERN_INFO "btrfsic: error, kmalloc failed!\n");
                        btrfsic_release_block_ctx(next_block_ctx);
                        *next_blockp = NULL;
                        return -1;
                }

                did_alloc_block_link = 1;
                l->block_ref_to = next_block;
                l->block_ref_from = block;
                l->ref_cnt = 1;
                l->parent_generation = parent_generation;

                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        btrfsic_print_add_link(state, l);

                list_add(&l->node_ref_to, &block->ref_to_list);
                list_add(&l->node_ref_from, &next_block->ref_from_list);

                btrfsic_block_link_hashtable_add(l,
                                                 &state->block_link_hashtable);
        } else {
                did_alloc_block_link = 0;
                if (0 == limit_nesting) {
                        l->ref_cnt++;
                        l->parent_generation = parent_generation;
                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                btrfsic_print_add_link(state, l);
                }
        }

        if (limit_nesting > 0 && did_alloc_block_link) {
                ret = btrfsic_read_block(state, next_block_ctx);
                if (ret < (int)next_block_ctx->len) {
                        printk(KERN_INFO
                               "btrfsic: read block @logical %llu failed!\n",
                               (unsigned long long)next_bytenr);
                        btrfsic_release_block_ctx(next_block_ctx);
                        *next_blockp = NULL;
                        return -1;
                }

                *next_blockp = next_block;
        } else {
                *next_blockp = NULL;
        }
        (*mirror_nump)++;

        return 0;
}

static int btrfsic_handle_extent_data(
                struct btrfsic_state *state,
                struct btrfsic_block *block,
                struct btrfsic_block_data_ctx *block_ctx,
                u32 item_offset, int force_iodone_flag)
{
        int ret;
        struct btrfs_file_extent_item file_extent_item;
        u64 file_extent_item_offset;
        u64 next_bytenr;
        u64 num_bytes;
        u64 generation;
        struct btrfsic_block_link *l;

        file_extent_item_offset = offsetof(struct btrfs_leaf, items) +
                                  item_offset;
        if (file_extent_item_offset +
            offsetof(struct btrfs_file_extent_item, disk_num_bytes) >
            block_ctx->len) {
                printk(KERN_INFO
                       "btrfsic: file item out of bounce at logical %llu, dev %s\n",
                       block_ctx->start, block_ctx->dev->name);
                return -1;
        }

        btrfsic_read_from_block_data(block_ctx, &file_extent_item,
                file_extent_item_offset,
                offsetof(struct btrfs_file_extent_item, disk_num_bytes));
        if (BTRFS_FILE_EXTENT_REG != file_extent_item.type ||
            ((u64)0) == le64_to_cpu(file_extent_item.disk_bytenr)) {
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERY_VERBOSE)
                        printk(KERN_INFO "extent_data: type %u, disk_bytenr = %llu\n",
                               file_extent_item.type,
                               (unsigned long long)
                               le64_to_cpu(file_extent_item.disk_bytenr));
                return 0;
        }

        if (file_extent_item_offset + sizeof(struct btrfs_file_extent_item) >
            block_ctx->len) {
                printk(KERN_INFO
                       "btrfsic: file item out of bounce at logical %llu, dev %s\n",
                       block_ctx->start, block_ctx->dev->name);
                return -1;
        }
        btrfsic_read_from_block_data(block_ctx, &file_extent_item,
                                     file_extent_item_offset,
                                     sizeof(struct btrfs_file_extent_item));
        next_bytenr = le64_to_cpu(file_extent_item.disk_bytenr) +
                      le64_to_cpu(file_extent_item.offset);
        generation = le64_to_cpu(file_extent_item.generation);
        num_bytes = le64_to_cpu(file_extent_item.num_bytes);
        generation = le64_to_cpu(file_extent_item.generation);

        if (state->print_mask & BTRFSIC_PRINT_MASK_VERY_VERBOSE)
                printk(KERN_INFO "extent_data: type %u, disk_bytenr = %llu,"
                       " offset = %llu, num_bytes = %llu\n",
                       file_extent_item.type,
                       (unsigned long long)
                       le64_to_cpu(file_extent_item.disk_bytenr),
                       (unsigned long long)le64_to_cpu(file_extent_item.offset),
                       (unsigned long long)num_bytes);
        while (num_bytes > 0) {
                u32 chunk_len;
                int num_copies;
                int mirror_num;

                if (num_bytes > state->datablock_size)
                        chunk_len = state->datablock_size;
                else
                        chunk_len = num_bytes;

                num_copies =
                    btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                     next_bytenr, state->datablock_size);
                if (state->print_mask & BTRFSIC_PRINT_MASK_NUM_COPIES)
                        printk(KERN_INFO "num_copies(log_bytenr=%llu) = %d\n",
                               (unsigned long long)next_bytenr, num_copies);
                for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                        struct btrfsic_block_data_ctx next_block_ctx;
                        struct btrfsic_block *next_block;
                        int block_was_created;

                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO "btrfsic_handle_extent_data("
                                       "mirror_num=%d)\n", mirror_num);
                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERY_VERBOSE)
                                printk(KERN_INFO
                                       "\tdisk_bytenr = %llu, num_bytes %u\n",
                                       (unsigned long long)next_bytenr,
                                       chunk_len);
                        ret = btrfsic_map_block(state, next_bytenr,
                                                chunk_len, &next_block_ctx,
                                                mirror_num);
                        if (ret) {
                                printk(KERN_INFO
                                       "btrfsic: btrfsic_map_block(@%llu,"
                                       " mirror=%d) failed!\n",
                                       (unsigned long long)next_bytenr,
                                       mirror_num);
                                return -1;
                        }

                        next_block = btrfsic_block_lookup_or_add(
                                        state,
                                        &next_block_ctx,
                                        "referenced ",
                                        0,
                                        force_iodone_flag,
                                        !force_iodone_flag,
                                        mirror_num,
                                        &block_was_created);
                        if (NULL == next_block) {
                                printk(KERN_INFO
                                       "btrfsic: error, kmalloc failed!\n");
                                btrfsic_release_block_ctx(&next_block_ctx);
                                return -1;
                        }
                        if (!block_was_created) {
                                if (next_block->logical_bytenr != next_bytenr &&
                                    !(!next_block->is_metadata &&
                                      0 == next_block->logical_bytenr)) {
                                        printk(KERN_INFO
                                               "Referenced block"
                                               " @%llu (%s/%llu/%d)"
                                               " found in hash table, D,"
                                               " bytenr mismatch"
                                               " (!= stored %llu).\n",
                                               (unsigned long long)next_bytenr,
                                               next_block_ctx.dev->name,
                                               (unsigned long long)
                                               next_block_ctx.dev_bytenr,
                                               mirror_num,
                                               (unsigned long long)
                                               next_block->logical_bytenr);
                                }
                                next_block->logical_bytenr = next_bytenr;
                                next_block->mirror_num = mirror_num;
                        }

                        l = btrfsic_block_link_lookup_or_add(state,
                                                             &next_block_ctx,
                                                             next_block, block,
                                                             generation);
                        btrfsic_release_block_ctx(&next_block_ctx);
                        if (NULL == l)
                                return -1;
                }

                next_bytenr += chunk_len;
                num_bytes -= chunk_len;
        }

        return 0;
}

static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
                             struct btrfsic_block_data_ctx *block_ctx_out,
                             int mirror_num)
{
        int ret;
        u64 length;
        struct btrfs_bio *multi = NULL;
        struct btrfs_device *device;

        length = len;
        ret = btrfs_map_block(&state->root->fs_info->mapping_tree, READ,
                              bytenr, &length, &multi, mirror_num);

        device = multi->stripes[0].dev;
        block_ctx_out->dev = btrfsic_dev_state_lookup(device->bdev);
        block_ctx_out->dev_bytenr = multi->stripes[0].physical;
        block_ctx_out->start = bytenr;
        block_ctx_out->len = len;
        block_ctx_out->datav = NULL;
        block_ctx_out->pagev = NULL;
        block_ctx_out->mem_to_free = NULL;

        if (0 == ret)
                kfree(multi);
        if (NULL == block_ctx_out->dev) {
                ret = -ENXIO;
                printk(KERN_INFO "btrfsic: error, cannot lookup dev (#1)!\n");
        }

        return ret;
}

static int btrfsic_map_superblock(struct btrfsic_state *state, u64 bytenr,
                                  u32 len, struct block_device *bdev,
                                  struct btrfsic_block_data_ctx *block_ctx_out)
{
        block_ctx_out->dev = btrfsic_dev_state_lookup(bdev);
        block_ctx_out->dev_bytenr = bytenr;
        block_ctx_out->start = bytenr;
        block_ctx_out->len = len;
        block_ctx_out->datav = NULL;
        block_ctx_out->pagev = NULL;
        block_ctx_out->mem_to_free = NULL;
        if (NULL != block_ctx_out->dev) {
                return 0;
        } else {
                printk(KERN_INFO "btrfsic: error, cannot lookup dev (#2)!\n");
                return -ENXIO;
        }
}

static void btrfsic_release_block_ctx(struct btrfsic_block_data_ctx *block_ctx)
{
        if (block_ctx->mem_to_free) {
                unsigned int num_pages;

                BUG_ON(!block_ctx->datav);
                BUG_ON(!block_ctx->pagev);
                num_pages = (block_ctx->len + (u64)PAGE_CACHE_SIZE - 1) >>
                            PAGE_CACHE_SHIFT;
                while (num_pages > 0) {
                        num_pages--;
                        if (block_ctx->datav[num_pages]) {
                                kunmap(block_ctx->pagev[num_pages]);
                                block_ctx->datav[num_pages] = NULL;
                        }
                        if (block_ctx->pagev[num_pages]) {
                                __free_page(block_ctx->pagev[num_pages]);
                                block_ctx->pagev[num_pages] = NULL;
                        }
                }

                kfree(block_ctx->mem_to_free);
                block_ctx->mem_to_free = NULL;
                block_ctx->pagev = NULL;
                block_ctx->datav = NULL;
        }
}

static int btrfsic_read_block(struct btrfsic_state *state,
                              struct btrfsic_block_data_ctx *block_ctx)
{
        unsigned int num_pages;
        unsigned int i;
        u64 dev_bytenr;
        int ret;

        BUG_ON(block_ctx->datav);
        BUG_ON(block_ctx->pagev);
        BUG_ON(block_ctx->mem_to_free);
        if (block_ctx->dev_bytenr & ((u64)PAGE_CACHE_SIZE - 1)) {
                printk(KERN_INFO
                       "btrfsic: read_block() with unaligned bytenr %llu\n",
                       (unsigned long long)block_ctx->dev_bytenr);
                return -1;
        }

        num_pages = (block_ctx->len + (u64)PAGE_CACHE_SIZE - 1) >>
                    PAGE_CACHE_SHIFT;
        block_ctx->mem_to_free = kzalloc((sizeof(*block_ctx->datav) +
                                          sizeof(*block_ctx->pagev)) *
                                         num_pages, GFP_NOFS);
        if (!block_ctx->mem_to_free)
                return -1;
        block_ctx->datav = block_ctx->mem_to_free;
        block_ctx->pagev = (struct page **)(block_ctx->datav + num_pages);
        for (i = 0; i < num_pages; i++) {
                block_ctx->pagev[i] = alloc_page(GFP_NOFS);
                if (!block_ctx->pagev[i])
                        return -1;
        }

        dev_bytenr = block_ctx->dev_bytenr;
        for (i = 0; i < num_pages;) {
                struct bio *bio;
                unsigned int j;
                DECLARE_COMPLETION_ONSTACK(complete);

                bio = bio_alloc(GFP_NOFS, num_pages - i);
                if (!bio) {
                        printk(KERN_INFO
                               "btrfsic: bio_alloc() for %u pages failed!\n",
                               num_pages - i);
                        return -1;
                }
                bio->bi_bdev = block_ctx->dev->bdev;
                bio->bi_sector = dev_bytenr >> 9;
                bio->bi_end_io = btrfsic_complete_bio_end_io;
                bio->bi_private = &complete;

                for (j = i; j < num_pages; j++) {
                        ret = bio_add_page(bio, block_ctx->pagev[j],
                                           PAGE_CACHE_SIZE, 0);
                        if (PAGE_CACHE_SIZE != ret)
                                break;
                }
                if (j == i) {
                        printk(KERN_INFO
                               "btrfsic: error, failed to add a single page!\n");
                        return -1;
                }
                submit_bio(READ, bio);

                /* this will also unplug the queue */
                wait_for_completion(&complete);

                if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) {
                        printk(KERN_INFO
                               "btrfsic: read error at logical %llu dev %s!\n",
                               block_ctx->start, block_ctx->dev->name);
                        bio_put(bio);
                        return -1;
                }
                bio_put(bio);
                dev_bytenr += (j - i) * PAGE_CACHE_SIZE;
                i = j;
        }
        for (i = 0; i < num_pages; i++) {
                block_ctx->datav[i] = kmap(block_ctx->pagev[i]);
                if (!block_ctx->datav[i]) {
                        printk(KERN_INFO "btrfsic: kmap() failed (dev %s)!\n",
                               block_ctx->dev->name);
                        return -1;
                }
        }

        return block_ctx->len;
}

static void btrfsic_complete_bio_end_io(struct bio *bio, int err)
{
        complete((struct completion *)bio->bi_private);
}

static void btrfsic_dump_database(struct btrfsic_state *state)
{
        struct list_head *elem_all;

        BUG_ON(NULL == state);

        printk(KERN_INFO "all_blocks_list:\n");
        list_for_each(elem_all, &state->all_blocks_list) {
                const struct btrfsic_block *const b_all =
                    list_entry(elem_all, struct btrfsic_block,
                               all_blocks_node);
                struct list_head *elem_ref_to;
                struct list_head *elem_ref_from;

                printk(KERN_INFO "%c-block @%llu (%s/%llu/%d)\n",
                       btrfsic_get_block_type(state, b_all),
                       (unsigned long long)b_all->logical_bytenr,
                       b_all->dev_state->name,
                       (unsigned long long)b_all->dev_bytenr,
                       b_all->mirror_num);

                list_for_each(elem_ref_to, &b_all->ref_to_list) {
                        const struct btrfsic_block_link *const l =
                            list_entry(elem_ref_to,
                                       struct btrfsic_block_link,
                                       node_ref_to);

                        printk(KERN_INFO " %c @%llu (%s/%llu/%d)"
                               " refers %u* to"
                               " %c @%llu (%s/%llu/%d)\n",
                               btrfsic_get_block_type(state, b_all),
                               (unsigned long long)b_all->logical_bytenr,
                               b_all->dev_state->name,
                               (unsigned long long)b_all->dev_bytenr,
                               b_all->mirror_num,
                               l->ref_cnt,
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num);
                }

                list_for_each(elem_ref_from, &b_all->ref_from_list) {
                        const struct btrfsic_block_link *const l =
                            list_entry(elem_ref_from,
                                       struct btrfsic_block_link,
                                       node_ref_from);

                        printk(KERN_INFO " %c @%llu (%s/%llu/%d)"
                               " is ref %u* from"
                               " %c @%llu (%s/%llu/%d)\n",
                               btrfsic_get_block_type(state, b_all),
                               (unsigned long long)b_all->logical_bytenr,
                               b_all->dev_state->name,
                               (unsigned long long)b_all->dev_bytenr,
                               b_all->mirror_num,
                               l->ref_cnt,
                               btrfsic_get_block_type(state, l->block_ref_from),
                               (unsigned long long)
                               l->block_ref_from->logical_bytenr,
                               l->block_ref_from->dev_state->name,
                               (unsigned long long)
                               l->block_ref_from->dev_bytenr,
                               l->block_ref_from->mirror_num);
                }

                printk(KERN_INFO "\n");
        }
}

/*
 * Test whether the disk block contains a tree block (leaf or node)
 * (note that this test fails for the super block)
 */
static int btrfsic_test_for_metadata(struct btrfsic_state *state,
                                     char **datav, unsigned int num_pages)
{
        struct btrfs_header *h;
        u8 csum[BTRFS_CSUM_SIZE];
        u32 crc = ~(u32)0;
        unsigned int i;

        if (num_pages * PAGE_CACHE_SIZE < state->metablock_size)
                return 1; /* not metadata */
        num_pages = state->metablock_size >> PAGE_CACHE_SHIFT;
        h = (struct btrfs_header *)datav[0];

        if (memcmp(h->fsid, state->root->fs_info->fsid, BTRFS_UUID_SIZE))
                return 1;

        for (i = 0; i < num_pages; i++) {
                u8 *data = i ? datav[i] : (datav[i] + BTRFS_CSUM_SIZE);
                size_t sublen = i ? PAGE_CACHE_SIZE :
                                    (PAGE_CACHE_SIZE - BTRFS_CSUM_SIZE);

                crc = crc32c(crc, data, sublen);
        }
        btrfs_csum_final(crc, csum);
        if (memcmp(csum, h->csum, state->csum_size))
                return 1;

        return 0; /* is metadata */
}

static void btrfsic_process_written_block(struct btrfsic_dev_state *dev_state,
                                          u64 dev_bytenr, char **mapped_datav,
                                          unsigned int num_pages,
                                          struct bio *bio, int *bio_is_patched,
                                          struct buffer_head *bh,
                                          int submit_bio_bh_rw)
{
        int is_metadata;
        struct btrfsic_block *block;
        struct btrfsic_block_data_ctx block_ctx;
        int ret;
        struct btrfsic_state *state = dev_state->state;
        struct block_device *bdev = dev_state->bdev;
        unsigned int processed_len;

        if (NULL != bio_is_patched)
                *bio_is_patched = 0;

again:
        if (num_pages == 0)
                return;

        processed_len = 0;
        is_metadata = (0 == btrfsic_test_for_metadata(state, mapped_datav,
                                                      num_pages));

        block = btrfsic_block_hashtable_lookup(bdev, dev_bytenr,
                                               &state->block_hashtable);
        if (NULL != block) {
                u64 bytenr = 0;
                struct list_head *elem_ref_to;
                struct list_head *tmp_ref_to;

                if (block->is_superblock) {
                        bytenr = le64_to_cpu(((struct btrfs_super_block *)
                                              mapped_datav[0])->bytenr);
                        if (num_pages * PAGE_CACHE_SIZE <
                            BTRFS_SUPER_INFO_SIZE) {
                                printk(KERN_INFO
                                       "btrfsic: cannot work with too short bios!\n");
                                return;
                        }
                        is_metadata = 1;
                        BUG_ON(BTRFS_SUPER_INFO_SIZE & (PAGE_CACHE_SIZE - 1));
                        processed_len = BTRFS_SUPER_INFO_SIZE;
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_TREE_BEFORE_SB_WRITE) {
                                printk(KERN_INFO
                                       "[before new superblock is written]:\n");
                                btrfsic_dump_tree_sub(state, block, 0);
                        }
                }
                if (is_metadata) {
                        if (!block->is_superblock) {
                                if (num_pages * PAGE_CACHE_SIZE <
                                    state->metablock_size) {
                                        printk(KERN_INFO
                                               "btrfsic: cannot work with too short bios!\n");
                                        return;
                                }
                                processed_len = state->metablock_size;
                                bytenr = le64_to_cpu(((struct btrfs_header *)
                                                      mapped_datav[0])->bytenr);
                                btrfsic_cmp_log_and_dev_bytenr(state, bytenr,
                                                               dev_state,
                                                               dev_bytenr);
                        }
                        if (block->logical_bytenr != bytenr) {
                                printk(KERN_INFO
                                       "Written block @%llu (%s/%llu/%d)"
                                       " found in hash table, %c,"
                                       " bytenr mismatch"
                                       " (!= stored %llu).\n",
                                       (unsigned long long)bytenr,
                                       dev_state->name,
                                       (unsigned long long)dev_bytenr,
                                       block->mirror_num,
                                       btrfsic_get_block_type(state, block),
                                       (unsigned long long)
                                       block->logical_bytenr);
                                block->logical_bytenr = bytenr;
                        } else if (state->print_mask &
                                   BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO
                                       "Written block @%llu (%s/%llu/%d)"
                                       " found in hash table, %c.\n",
                                       (unsigned long long)bytenr,
                                       dev_state->name,
                                       (unsigned long long)dev_bytenr,
                                       block->mirror_num,
                                       btrfsic_get_block_type(state, block));
                } else {
                        if (num_pages * PAGE_CACHE_SIZE <
                            state->datablock_size) {
                                printk(KERN_INFO
                                       "btrfsic: cannot work with too short bios!\n");
                                return;
                        }
                        processed_len = state->datablock_size;
                        bytenr = block->logical_bytenr;
                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO
                                       "Written block @%llu (%s/%llu/%d)"
                                       " found in hash table, %c.\n",
                                       (unsigned long long)bytenr,
                                       dev_state->name,
                                       (unsigned long long)dev_bytenr,
                                       block->mirror_num,
                                       btrfsic_get_block_type(state, block));
                }

                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "ref_to_list: %cE, ref_from_list: %cE\n",
                               list_empty(&block->ref_to_list) ? ' ' : '!',
                               list_empty(&block->ref_from_list) ? ' ' : '!');
                if (btrfsic_is_block_ref_by_superblock(state, block, 0)) {
                        printk(KERN_INFO "btrfs: attempt to overwrite %c-block"
                               " @%llu (%s/%llu/%d), old(gen=%llu,"
                               " objectid=%llu, type=%d, offset=%llu),"
                               " new(gen=%llu),"
                               " which is referenced by most recent superblock"
                               " (superblockgen=%llu)!\n",
                               btrfsic_get_block_type(state, block),
                               (unsigned long long)bytenr,
                               dev_state->name,
                               (unsigned long long)dev_bytenr,
                               block->mirror_num,
                               (unsigned long long)block->generation,
                               (unsigned long long)
                               le64_to_cpu(block->disk_key.objectid),
                               block->disk_key.type,
                               (unsigned long long)
                               le64_to_cpu(block->disk_key.offset),
                               (unsigned long long)
                               le64_to_cpu(((struct btrfs_header *)
                                            mapped_datav[0])->generation),
                               (unsigned long long)
                               state->max_superblock_generation);
                        btrfsic_dump_tree(state);
                }

                if (!block->is_iodone && !block->never_written) {
                        printk(KERN_INFO "btrfs: attempt to overwrite %c-block"
                               " @%llu (%s/%llu/%d), oldgen=%llu, newgen=%llu,"
                               " which is not yet iodone!\n",
                               btrfsic_get_block_type(state, block),

                               (unsigned long long)bytenr,
                               dev_state->name,
                               (unsigned long long)dev_bytenr,
                               block->mirror_num,
                               (unsigned long long)block->generation,
                               (unsigned long long)
                               le64_to_cpu(((struct btrfs_header *)
                                            mapped_datav[0])->generation));
                        /* it would not be safe to go on */
                        btrfsic_dump_tree(state);
                        goto continue_loop;
                }

                /*
                 * Clear all references of this block. Do not free
                 * the block itself even if is not referenced anymore
                 * because it still carries valueable information
                 * like whether it was ever written and IO completed.
                 */
                list_for_each_safe(elem_ref_to, tmp_ref_to,
                                   &block->ref_to_list) {
                        struct btrfsic_block_link *const l =
                            list_entry(elem_ref_to,
                                       struct btrfsic_block_link,
                                       node_ref_to);

                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                btrfsic_print_rem_link(state, l);
                        l->ref_cnt--;
                        if (0 == l->ref_cnt) {
                                list_del(&l->node_ref_to);
                                list_del(&l->node_ref_from);
                                btrfsic_block_link_hashtable_remove(l);
                                btrfsic_block_link_free(l);
                        }
                }

                if (block->is_superblock)
                        ret = btrfsic_map_superblock(state, bytenr,
                                                     processed_len,
                                                     bdev, &block_ctx);
                else
                        ret = btrfsic_map_block(state, bytenr, processed_len,
                                                &block_ctx, 0);
                if (ret) {
                        printk(KERN_INFO
                               "btrfsic: btrfsic_map_block(root @%llu)"
                               " failed!\n", (unsigned long long)bytenr);
                        goto continue_loop;
                }
                block_ctx.datav = mapped_datav;
                /* the following is required in case of writes to mirrors,
                 * use the same that was used for the lookup */
                block_ctx.dev = dev_state;
                block_ctx.dev_bytenr = dev_bytenr;

                if (is_metadata || state->include_extent_data) {
                        block->never_written = 0;
                        block->iodone_w_error = 0;
                        if (NULL != bio) {
                                block->is_iodone = 0;
                                BUG_ON(NULL == bio_is_patched);
                                if (!*bio_is_patched) {
                                        block->orig_bio_bh_private =
                                            bio->bi_private;
                                        block->orig_bio_bh_end_io.bio =
                                            bio->bi_end_io;
                                        block->next_in_same_bio = NULL;
                                        bio->bi_private = block;
                                        bio->bi_end_io = btrfsic_bio_end_io;
                                        *bio_is_patched = 1;
                                } else {
                                        struct btrfsic_block *chained_block =
                                            (struct btrfsic_block *)
                                            bio->bi_private;

                                        BUG_ON(NULL == chained_block);
                                        block->orig_bio_bh_private =
                                            chained_block->orig_bio_bh_private;
                                        block->orig_bio_bh_end_io.bio =
                                            chained_block->orig_bio_bh_end_io.
                                            bio;
                                        block->next_in_same_bio = chained_block;
                                        bio->bi_private = block;
                                }
                        } else if (NULL != bh) {
                                block->is_iodone = 0;
                                block->orig_bio_bh_private = bh->b_private;
                                block->orig_bio_bh_end_io.bh = bh->b_end_io;
                                block->next_in_same_bio = NULL;
                                bh->b_private = block;
                                bh->b_end_io = btrfsic_bh_end_io;
                        } else {
                                block->is_iodone = 1;
                                block->orig_bio_bh_private = NULL;
                                block->orig_bio_bh_end_io.bio = NULL;
                                block->next_in_same_bio = NULL;
                        }
                }

                block->flush_gen = dev_state->last_flush_gen + 1;
                block->submit_bio_bh_rw = submit_bio_bh_rw;
                if (is_metadata) {
                        block->logical_bytenr = bytenr;
                        block->is_metadata = 1;
                        if (block->is_superblock) {
                                BUG_ON(PAGE_CACHE_SIZE !=
                                       BTRFS_SUPER_INFO_SIZE);
                                ret = btrfsic_process_written_superblock(
                                                state,
                                                block,
                                                (struct btrfs_super_block *)
                                                mapped_datav[0]);
                                if (state->print_mask &
                                    BTRFSIC_PRINT_MASK_TREE_AFTER_SB_WRITE) {
                                        printk(KERN_INFO
                                        "[after new superblock is written]:\n");
                                        btrfsic_dump_tree_sub(state, block, 0);
                                }
                        } else {
                                block->mirror_num = 0;  /* unknown */
                                ret = btrfsic_process_metablock(
                                                state,
                                                block,
                                                &block_ctx,
                                                0, 0);
                        }
                        if (ret)
                                printk(KERN_INFO
                                       "btrfsic: btrfsic_process_metablock"
                                       "(root @%llu) failed!\n",
                                       (unsigned long long)dev_bytenr);
                } else {
                        block->is_metadata = 0;
                        block->mirror_num = 0;  /* unknown */
                        block->generation = BTRFSIC_GENERATION_UNKNOWN;
                        if (!state->include_extent_data
                            && list_empty(&block->ref_from_list)) {
                                /*
                                 * disk block is overwritten with extent
                                 * data (not meta data) and we are configured
                                 * to not include extent data: take the
                                 * chance and free the block's memory
                                 */
                                btrfsic_block_hashtable_remove(block);
                                list_del(&block->all_blocks_node);
                                btrfsic_block_free(block);
                        }
                }
                btrfsic_release_block_ctx(&block_ctx);
        } else {
                /* block has not been found in hash table */
                u64 bytenr;

                if (!is_metadata) {
                        processed_len = state->datablock_size;
                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO "Written block (%s/%llu/?)"
                                       " !found in hash table, D.\n",
                                       dev_state->name,
                                       (unsigned long long)dev_bytenr);
                        if (!state->include_extent_data) {
                                /* ignore that written D block */
                                goto continue_loop;
                        }

                        /* this is getting ugly for the
                         * include_extent_data case... */
                        bytenr = 0;     /* unknown */
                        block_ctx.start = bytenr;
                        block_ctx.len = processed_len;
                        block_ctx.mem_to_free = NULL;
                        block_ctx.pagev = NULL;
                } else {
                        processed_len = state->metablock_size;
                        bytenr = le64_to_cpu(((struct btrfs_header *)
                                              mapped_datav[0])->bytenr);
                        btrfsic_cmp_log_and_dev_bytenr(state, bytenr, dev_state,
                                                       dev_bytenr);
                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO
                                       "Written block @%llu (%s/%llu/?)"
                                       " !found in hash table, M.\n",
                                       (unsigned long long)bytenr,
                                       dev_state->name,
                                       (unsigned long long)dev_bytenr);

                        ret = btrfsic_map_block(state, bytenr, processed_len,
                                                &block_ctx, 0);
                        if (ret) {
                                printk(KERN_INFO
                                       "btrfsic: btrfsic_map_block(root @%llu)"
                                       " failed!\n",
                                       (unsigned long long)dev_bytenr);
                                goto continue_loop;
                        }
                }
                block_ctx.datav = mapped_datav;
                /* the following is required in case of writes to mirrors,
                 * use the same that was used for the lookup */
                block_ctx.dev = dev_state;
                block_ctx.dev_bytenr = dev_bytenr;

                block = btrfsic_block_alloc();
                if (NULL == block) {
                        printk(KERN_INFO "btrfsic: error, kmalloc failed!\n");
                        btrfsic_release_block_ctx(&block_ctx);
                        goto continue_loop;
                }
                block->dev_state = dev_state;
                block->dev_bytenr = dev_bytenr;
                block->logical_bytenr = bytenr;
                block->is_metadata = is_metadata;
                block->never_written = 0;
                block->iodone_w_error = 0;
                block->mirror_num = 0;  /* unknown */
                block->flush_gen = dev_state->last_flush_gen + 1;
                block->submit_bio_bh_rw = submit_bio_bh_rw;
                if (NULL != bio) {
                        block->is_iodone = 0;
                        BUG_ON(NULL == bio_is_patched);
                        if (!*bio_is_patched) {
                                block->orig_bio_bh_private = bio->bi_private;
                                block->orig_bio_bh_end_io.bio = bio->bi_end_io;
                                block->next_in_same_bio = NULL;
                                bio->bi_private = block;
                                bio->bi_end_io = btrfsic_bio_end_io;
                                *bio_is_patched = 1;
                        } else {
                                struct btrfsic_block *chained_block =
                                    (struct btrfsic_block *)
                                    bio->bi_private;

                                BUG_ON(NULL == chained_block);
                                block->orig_bio_bh_private =
                                    chained_block->orig_bio_bh_private;
                                block->orig_bio_bh_end_io.bio =
                                    chained_block->orig_bio_bh_end_io.bio;
                                block->next_in_same_bio = chained_block;
                                bio->bi_private = block;
                        }
                } else if (NULL != bh) {
                        block->is_iodone = 0;
                        block->orig_bio_bh_private = bh->b_private;
                        block->orig_bio_bh_end_io.bh = bh->b_end_io;
                        block->next_in_same_bio = NULL;
                        bh->b_private = block;
                        bh->b_end_io = btrfsic_bh_end_io;
                } else {
                        block->is_iodone = 1;
                        block->orig_bio_bh_private = NULL;
                        block->orig_bio_bh_end_io.bio = NULL;
                        block->next_in_same_bio = NULL;
                }
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "New written %c-block @%llu (%s/%llu/%d)\n",
                               is_metadata ? 'M' : 'D',
                               (unsigned long long)block->logical_bytenr,
                               block->dev_state->name,
                               (unsigned long long)block->dev_bytenr,
                               block->mirror_num);
                list_add(&block->all_blocks_node, &state->all_blocks_list);
                btrfsic_block_hashtable_add(block, &state->block_hashtable);

                if (is_metadata) {
                        ret = btrfsic_process_metablock(state, block,
                                                        &block_ctx, 0, 0);
                        if (ret)
                                printk(KERN_INFO
                                       "btrfsic: process_metablock(root @%llu)"
                                       " failed!\n",
                                       (unsigned long long)dev_bytenr);
                }
                btrfsic_release_block_ctx(&block_ctx);
        }

continue_loop:
        BUG_ON(!processed_len);
        dev_bytenr += processed_len;
        mapped_datav += processed_len >> PAGE_CACHE_SHIFT;
        num_pages -= processed_len >> PAGE_CACHE_SHIFT;
        goto again;
}

static void btrfsic_bio_end_io(struct bio *bp, int bio_error_status)
{
        struct btrfsic_block *block = (struct btrfsic_block *)bp->bi_private;
        int iodone_w_error;

        /* mutex is not held! This is not save if IO is not yet completed
         * on umount */
        iodone_w_error = 0;
        if (bio_error_status)
                iodone_w_error = 1;

        BUG_ON(NULL == block);
        bp->bi_private = block->orig_bio_bh_private;
        bp->bi_end_io = block->orig_bio_bh_end_io.bio;

        do {
                struct btrfsic_block *next_block;
                struct btrfsic_dev_state *const dev_state = block->dev_state;

                if ((dev_state->state->print_mask &
                     BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
                        printk(KERN_INFO
                               "bio_end_io(err=%d) for %c @%llu (%s/%llu/%d)\n",
                               bio_error_status,
                               btrfsic_get_block_type(dev_state->state, block),
                               (unsigned long long)block->logical_bytenr,
                               dev_state->name,
                               (unsigned long long)block->dev_bytenr,
                               block->mirror_num);
                next_block = block->next_in_same_bio;
                block->iodone_w_error = iodone_w_error;
                if (block->submit_bio_bh_rw & REQ_FLUSH) {
                        dev_state->last_flush_gen++;
                        if ((dev_state->state->print_mask &
                             BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
                                printk(KERN_INFO
                                       "bio_end_io() new %s flush_gen=%llu\n",
                                       dev_state->name,
                                       (unsigned long long)
                                       dev_state->last_flush_gen);
                }
                if (block->submit_bio_bh_rw & REQ_FUA)
                        block->flush_gen = 0; /* FUA completed means block is
                                               * on disk */
                block->is_iodone = 1; /* for FLUSH, this releases the block */
                block = next_block;
        } while (NULL != block);

        bp->bi_end_io(bp, bio_error_status);
}

static void btrfsic_bh_end_io(struct buffer_head *bh, int uptodate)
{
        struct btrfsic_block *block = (struct btrfsic_block *)bh->b_private;
        int iodone_w_error = !uptodate;
        struct btrfsic_dev_state *dev_state;

        BUG_ON(NULL == block);
        dev_state = block->dev_state;
        if ((dev_state->state->print_mask & BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
                printk(KERN_INFO
                       "bh_end_io(error=%d) for %c @%llu (%s/%llu/%d)\n",
                       iodone_w_error,
                       btrfsic_get_block_type(dev_state->state, block),
                       (unsigned long long)block->logical_bytenr,
                       block->dev_state->name,
                       (unsigned long long)block->dev_bytenr,
                       block->mirror_num);

        block->iodone_w_error = iodone_w_error;
        if (block->submit_bio_bh_rw & REQ_FLUSH) {
                dev_state->last_flush_gen++;
                if ((dev_state->state->print_mask &
                     BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
                        printk(KERN_INFO
                               "bh_end_io() new %s flush_gen=%llu\n",
                               dev_state->name,
                               (unsigned long long)dev_state->last_flush_gen);
        }
        if (block->submit_bio_bh_rw & REQ_FUA)
                block->flush_gen = 0; /* FUA completed means block is on disk */

        bh->b_private = block->orig_bio_bh_private;
        bh->b_end_io = block->orig_bio_bh_end_io.bh;
        block->is_iodone = 1; /* for FLUSH, this releases the block */
        bh->b_end_io(bh, uptodate);
}

static int btrfsic_process_written_superblock(
                struct btrfsic_state *state,
                struct btrfsic_block *const superblock,
                struct btrfs_super_block *const super_hdr)
{
        int pass;

        superblock->generation = btrfs_super_generation(super_hdr);
        if (!(superblock->generation > state->max_superblock_generation ||
              0 == state->max_superblock_generation)) {
                if (state->print_mask & BTRFSIC_PRINT_MASK_SUPERBLOCK_WRITE)
                        printk(KERN_INFO
                               "btrfsic: superblock @%llu (%s/%llu/%d)"
                               " with old gen %llu <= %llu\n",
                               (unsigned long long)superblock->logical_bytenr,
                               superblock->dev_state->name,
                               (unsigned long long)superblock->dev_bytenr,
                               superblock->mirror_num,
                               (unsigned long long)
                               btrfs_super_generation(super_hdr),
                               (unsigned long long)
                               state->max_superblock_generation);
        } else {
                if (state->print_mask & BTRFSIC_PRINT_MASK_SUPERBLOCK_WRITE)
                        printk(KERN_INFO
                               "btrfsic: got new superblock @%llu (%s/%llu/%d)"
                               " with new gen %llu > %llu\n",
                               (unsigned long long)superblock->logical_bytenr,
                               superblock->dev_state->name,
                               (unsigned long long)superblock->dev_bytenr,
                               superblock->mirror_num,
                               (unsigned long long)
                               btrfs_super_generation(super_hdr),
                               (unsigned long long)
                               state->max_superblock_generation);

                state->max_superblock_generation =
                    btrfs_super_generation(super_hdr);
                state->latest_superblock = superblock;
        }

        for (pass = 0; pass < 3; pass++) {
                int ret;
                u64 next_bytenr;
                struct btrfsic_block *next_block;
                struct btrfsic_block_data_ctx tmp_next_block_ctx;
                struct btrfsic_block_link *l;
                int num_copies;
                int mirror_num;
                const char *additional_string = NULL;
                struct btrfs_disk_key tmp_disk_key;

                tmp_disk_key.type = BTRFS_ROOT_ITEM_KEY;
                tmp_disk_key.offset = 0;

                switch (pass) {
                case 0:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_ROOT_TREE_OBJECTID);
                        additional_string = "root ";
                        next_bytenr = btrfs_super_root(super_hdr);
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "root@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                case 1:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_CHUNK_TREE_OBJECTID);
                        additional_string = "chunk ";
                        next_bytenr = btrfs_super_chunk_root(super_hdr);
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "chunk@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                case 2:
                        tmp_disk_key.objectid =
                            cpu_to_le64(BTRFS_TREE_LOG_OBJECTID);
                        additional_string = "log ";
                        next_bytenr = btrfs_super_log_root(super_hdr);
                        if (0 == next_bytenr)
                                continue;
                        if (state->print_mask &
                            BTRFSIC_PRINT_MASK_ROOT_CHUNK_LOG_TREE_LOCATION)
                                printk(KERN_INFO "log@%llu\n",
                                       (unsigned long long)next_bytenr);
                        break;
                }

                num_copies =
                    btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                     next_bytenr, BTRFS_SUPER_INFO_SIZE);
                if (state->print_mask & BTRFSIC_PRINT_MASK_NUM_COPIES)
                        printk(KERN_INFO "num_copies(log_bytenr=%llu) = %d\n",
                               (unsigned long long)next_bytenr, num_copies);
                for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                        int was_created;

                        if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                                printk(KERN_INFO
                                       "btrfsic_process_written_superblock("
                                       "mirror_num=%d)\n", mirror_num);
                        ret = btrfsic_map_block(state, next_bytenr,
                                                BTRFS_SUPER_INFO_SIZE,
                                                &tmp_next_block_ctx,
                                                mirror_num);
                        if (ret) {
                                printk(KERN_INFO
                                       "btrfsic: btrfsic_map_block(@%llu,"
                                       " mirror=%d) failed!\n",
                                       (unsigned long long)next_bytenr,
                                       mirror_num);
                                return -1;
                        }

                        next_block = btrfsic_block_lookup_or_add(
                                        state,
                                        &tmp_next_block_ctx,
                                        additional_string,
                                        1, 0, 1,
                                        mirror_num,
                                        &was_created);
                        if (NULL == next_block) {
                                printk(KERN_INFO
                                       "btrfsic: error, kmalloc failed!\n");
                                btrfsic_release_block_ctx(&tmp_next_block_ctx);
                                return -1;
                        }

                        next_block->disk_key = tmp_disk_key;
                        if (was_created)
                                next_block->generation =
                                    BTRFSIC_GENERATION_UNKNOWN;
                        l = btrfsic_block_link_lookup_or_add(
                                        state,
                                        &tmp_next_block_ctx,
                                        next_block,
                                        superblock,
                                        BTRFSIC_GENERATION_UNKNOWN);
                        btrfsic_release_block_ctx(&tmp_next_block_ctx);
                        if (NULL == l)
                                return -1;
                }
        }

        if (-1 == btrfsic_check_all_ref_blocks(state, superblock, 0)) {
                WARN_ON(1);
                btrfsic_dump_tree(state);
        }

        return 0;
}

static int btrfsic_check_all_ref_blocks(struct btrfsic_state *state,
                                        struct btrfsic_block *const block,
                                        int recursion_level)
{
        struct list_head *elem_ref_to;
        int ret = 0;

        if (recursion_level >= 3 + BTRFS_MAX_LEVEL) {
                /*
                 * Note that this situation can happen and does not
                 * indicate an error in regular cases. It happens
                 * when disk blocks are freed and later reused.
                 * The check-integrity module is not aware of any
                 * block free operations, it just recognizes block
                 * write operations. Therefore it keeps the linkage
                 * information for a block until a block is
                 * rewritten. This can temporarily cause incorrect
                 * and even circular linkage informations. This
                 * causes no harm unless such blocks are referenced
                 * by the most recent super block.
                 */
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "btrfsic: abort cyclic linkage (case 1).\n");

                return ret;
        }

        /*
         * This algorithm is recursive because the amount of used stack
         * space is very small and the max recursion depth is limited.
         */
        list_for_each(elem_ref_to, &block->ref_to_list) {
                const struct btrfsic_block_link *const l =
                    list_entry(elem_ref_to, struct btrfsic_block_link,
                               node_ref_to);

                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "rl=%d, %c @%llu (%s/%llu/%d)"
                               " %u* refers to %c @%llu (%s/%llu/%d)\n",
                               recursion_level,
                               btrfsic_get_block_type(state, block),
                               (unsigned long long)block->logical_bytenr,
                               block->dev_state->name,
                               (unsigned long long)block->dev_bytenr,
                               block->mirror_num,
                               l->ref_cnt,
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num);
                if (l->block_ref_to->never_written) {
                        printk(KERN_INFO "btrfs: attempt to write superblock"
                               " which references block %c @%llu (%s/%llu/%d)"
                               " which is never written!\n",
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num);
                        ret = -1;
                } else if (!l->block_ref_to->is_iodone) {
                        printk(KERN_INFO "btrfs: attempt to write superblock"
                               " which references block %c @%llu (%s/%llu/%d)"
                               " which is not yet iodone!\n",
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num);
                        ret = -1;
                } else if (l->parent_generation !=
                           l->block_ref_to->generation &&
                           BTRFSIC_GENERATION_UNKNOWN !=
                           l->parent_generation &&
                           BTRFSIC_GENERATION_UNKNOWN !=
                           l->block_ref_to->generation) {
                        printk(KERN_INFO "btrfs: attempt to write superblock"
                               " which references block %c @%llu (%s/%llu/%d)"
                               " with generation %llu !="
                               " parent generation %llu!\n",
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num,
                               (unsigned long long)l->block_ref_to->generation,
                               (unsigned long long)l->parent_generation);
                        ret = -1;
                } else if (l->block_ref_to->flush_gen >
                           l->block_ref_to->dev_state->last_flush_gen) {
                        printk(KERN_INFO "btrfs: attempt to write superblock"
                               " which references block %c @%llu (%s/%llu/%d)"
                               " which is not flushed out of disk's write cache"
                               " (block flush_gen=%llu,"
                               " dev->flush_gen=%llu)!\n",
                               btrfsic_get_block_type(state, l->block_ref_to),
                               (unsigned long long)
                               l->block_ref_to->logical_bytenr,
                               l->block_ref_to->dev_state->name,
                               (unsigned long long)l->block_ref_to->dev_bytenr,
                               l->block_ref_to->mirror_num,
                               (unsigned long long)block->flush_gen,
                               (unsigned long long)
                               l->block_ref_to->dev_state->last_flush_gen);
                        ret = -1;
                } else if (-1 == btrfsic_check_all_ref_blocks(state,
                                                              l->block_ref_to,
                                                              recursion_level +
                                                              1)) {
                        ret = -1;
                }
        }

        return ret;
}

static int btrfsic_is_block_ref_by_superblock(
                const struct btrfsic_state *state,
                const struct btrfsic_block *block,
                int recursion_level)
{
        struct list_head *elem_ref_from;

        if (recursion_level >= 3 + BTRFS_MAX_LEVEL) {
                /* refer to comment at "abort cyclic linkage (case 1)" */
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "btrfsic: abort cyclic linkage (case 2).\n");

                return 0;
        }

        /*
         * This algorithm is recursive because the amount of used stack space
         * is very small and the max recursion depth is limited.
         */
        list_for_each(elem_ref_from, &block->ref_from_list) {
                const struct btrfsic_block_link *const l =
                    list_entry(elem_ref_from, struct btrfsic_block_link,
                               node_ref_from);

                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "rl=%d, %c @%llu (%s/%llu/%d)"
                               " is ref %u* from %c @%llu (%s/%llu/%d)\n",
                               recursion_level,
                               btrfsic_get_block_type(state, block),
                               (unsigned long long)block->logical_bytenr,
                               block->dev_state->name,
                               (unsigned long long)block->dev_bytenr,
                               block->mirror_num,
                               l->ref_cnt,
                               btrfsic_get_block_type(state, l->block_ref_from),
                               (unsigned long long)
                               l->block_ref_from->logical_bytenr,
                               l->block_ref_from->dev_state->name,
                               (unsigned long long)
                               l->block_ref_from->dev_bytenr,
                               l->block_ref_from->mirror_num);
                if (l->block_ref_from->is_superblock &&
                    state->latest_superblock->dev_bytenr ==
                    l->block_ref_from->dev_bytenr &&
                    state->latest_superblock->dev_state->bdev ==
                    l->block_ref_from->dev_state->bdev)
                        return 1;
                else if (btrfsic_is_block_ref_by_superblock(state,
                                                            l->block_ref_from,
                                                            recursion_level +
                                                            1))
                        return 1;
        }

        return 0;
}

static void btrfsic_print_add_link(const struct btrfsic_state *state,
                                   const struct btrfsic_block_link *l)
{
        printk(KERN_INFO
               "Add %u* link from %c @%llu (%s/%llu/%d)"
               " to %c @%llu (%s/%llu/%d).\n",
               l->ref_cnt,
               btrfsic_get_block_type(state, l->block_ref_from),
               (unsigned long long)l->block_ref_from->logical_bytenr,
               l->block_ref_from->dev_state->name,
               (unsigned long long)l->block_ref_from->dev_bytenr,
               l->block_ref_from->mirror_num,
               btrfsic_get_block_type(state, l->block_ref_to),
               (unsigned long long)l->block_ref_to->logical_bytenr,
               l->block_ref_to->dev_state->name,
               (unsigned long long)l->block_ref_to->dev_bytenr,
               l->block_ref_to->mirror_num);
}

static void btrfsic_print_rem_link(const struct btrfsic_state *state,
                                   const struct btrfsic_block_link *l)
{
        printk(KERN_INFO
               "Rem %u* link from %c @%llu (%s/%llu/%d)"
               " to %c @%llu (%s/%llu/%d).\n",
               l->ref_cnt,
               btrfsic_get_block_type(state, l->block_ref_from),
               (unsigned long long)l->block_ref_from->logical_bytenr,
               l->block_ref_from->dev_state->name,
               (unsigned long long)l->block_ref_from->dev_bytenr,
               l->block_ref_from->mirror_num,
               btrfsic_get_block_type(state, l->block_ref_to),
               (unsigned long long)l->block_ref_to->logical_bytenr,
               l->block_ref_to->dev_state->name,
               (unsigned long long)l->block_ref_to->dev_bytenr,
               l->block_ref_to->mirror_num);
}

static char btrfsic_get_block_type(const struct btrfsic_state *state,
                                   const struct btrfsic_block *block)
{
        if (block->is_superblock &&
            state->latest_superblock->dev_bytenr == block->dev_bytenr &&
            state->latest_superblock->dev_state->bdev == block->dev_state->bdev)
                return 'S';
        else if (block->is_superblock)
                return 's';
        else if (block->is_metadata)
                return 'M';
        else
                return 'D';
}

static void btrfsic_dump_tree(const struct btrfsic_state *state)
{
        btrfsic_dump_tree_sub(state, state->latest_superblock, 0);
}

static void btrfsic_dump_tree_sub(const struct btrfsic_state *state,
                                  const struct btrfsic_block *block,
                                  int indent_level)
{
        struct list_head *elem_ref_to;
        int indent_add;
        static char buf[80];
        int cursor_position;

        /*
         * Should better fill an on-stack buffer with a complete line and
         * dump it at once when it is time to print a newline character.
         */

        /*
         * This algorithm is recursive because the amount of used stack space
         * is very small and the max recursion depth is limited.
         */
        indent_add = sprintf(buf, "%c-%llu(%s/%llu/%d)",
                             btrfsic_get_block_type(state, block),
                             (unsigned long long)block->logical_bytenr,
                             block->dev_state->name,
                             (unsigned long long)block->dev_bytenr,
                             block->mirror_num);
        if (indent_level + indent_add > BTRFSIC_TREE_DUMP_MAX_INDENT_LEVEL) {
                printk("[...]\n");
                return;
        }
        printk(buf);
        indent_level += indent_add;
        if (list_empty(&block->ref_to_list)) {
                printk("\n");
                return;
        }
        if (block->mirror_num > 1 &&
            !(state->print_mask & BTRFSIC_PRINT_MASK_TREE_WITH_ALL_MIRRORS)) {
                printk(" [...]\n");
                return;
        }

        cursor_position = indent_level;
        list_for_each(elem_ref_to, &block->ref_to_list) {
                const struct btrfsic_block_link *const l =
                    list_entry(elem_ref_to, struct btrfsic_block_link,
                               node_ref_to);

                while (cursor_position < indent_level) {
                        printk(" ");
                        cursor_position++;
                }
                if (l->ref_cnt > 1)
                        indent_add = sprintf(buf, " %d*--> ", l->ref_cnt);
                else
                        indent_add = sprintf(buf, " --> ");
                if (indent_level + indent_add >
                    BTRFSIC_TREE_DUMP_MAX_INDENT_LEVEL) {
                        printk("[...]\n");
                        cursor_position = 0;
                        continue;
                }

                printk(buf);

                btrfsic_dump_tree_sub(state, l->block_ref_to,
                                      indent_level + indent_add);
                cursor_position = 0;
        }
}

static struct btrfsic_block_link *btrfsic_block_link_lookup_or_add(
                struct btrfsic_state *state,
                struct btrfsic_block_data_ctx *next_block_ctx,
                struct btrfsic_block *next_block,
                struct btrfsic_block *from_block,
                u64 parent_generation)
{
        struct btrfsic_block_link *l;

        l = btrfsic_block_link_hashtable_lookup(next_block_ctx->dev->bdev,
                                                next_block_ctx->dev_bytenr,
                                                from_block->dev_state->bdev,
                                                from_block->dev_bytenr,
                                                &state->block_link_hashtable);
        if (NULL == l) {
                l = btrfsic_block_link_alloc();
                if (NULL == l) {
                        printk(KERN_INFO
                               "btrfsic: error, kmalloc" " failed!\n");
                        return NULL;
                }

                l->block_ref_to = next_block;
                l->block_ref_from = from_block;
                l->ref_cnt = 1;
                l->parent_generation = parent_generation;

                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        btrfsic_print_add_link(state, l);

                list_add(&l->node_ref_to, &from_block->ref_to_list);
                list_add(&l->node_ref_from, &next_block->ref_from_list);

                btrfsic_block_link_hashtable_add(l,
                                                 &state->block_link_hashtable);
        } else {
                l->ref_cnt++;
                l->parent_generation = parent_generation;
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        btrfsic_print_add_link(state, l);
        }

        return l;
}

static struct btrfsic_block *btrfsic_block_lookup_or_add(
                struct btrfsic_state *state,
                struct btrfsic_block_data_ctx *block_ctx,
                const char *additional_string,
                int is_metadata,
                int is_iodone,
                int never_written,
                int mirror_num,
                int *was_created)
{
        struct btrfsic_block *block;

        block = btrfsic_block_hashtable_lookup(block_ctx->dev->bdev,
                                               block_ctx->dev_bytenr,
                                               &state->block_hashtable);
        if (NULL == block) {
                struct btrfsic_dev_state *dev_state;

                block = btrfsic_block_alloc();
                if (NULL == block) {
                        printk(KERN_INFO "btrfsic: error, kmalloc failed!\n");
                        return NULL;
                }
                dev_state = btrfsic_dev_state_lookup(block_ctx->dev->bdev);
                if (NULL == dev_state) {
                        printk(KERN_INFO
                               "btrfsic: error, lookup dev_state failed!\n");
                        btrfsic_block_free(block);
                        return NULL;
                }
                block->dev_state = dev_state;
                block->dev_bytenr = block_ctx->dev_bytenr;
                block->logical_bytenr = block_ctx->start;
                block->is_metadata = is_metadata;
                block->is_iodone = is_iodone;
                block->never_written = never_written;
                block->mirror_num = mirror_num;
                if (state->print_mask & BTRFSIC_PRINT_MASK_VERBOSE)
                        printk(KERN_INFO
                               "New %s%c-block @%llu (%s/%llu/%d)\n",
                               additional_string,
                               btrfsic_get_block_type(state, block),
                               (unsigned long long)block->logical_bytenr,
                               dev_state->name,
                               (unsigned long long)block->dev_bytenr,
                               mirror_num);
                list_add(&block->all_blocks_node, &state->all_blocks_list);
                btrfsic_block_hashtable_add(block, &state->block_hashtable);
                if (NULL != was_created)
                        *was_created = 1;
        } else {
                if (NULL != was_created)
                        *was_created = 0;
        }

        return block;
}

static void btrfsic_cmp_log_and_dev_bytenr(struct btrfsic_state *state,
                                           u64 bytenr,
                                           struct btrfsic_dev_state *dev_state,
                                           u64 dev_bytenr)
{
        int num_copies;
        int mirror_num;
        int ret;
        struct btrfsic_block_data_ctx block_ctx;
        int match = 0;

        num_copies = btrfs_num_copies(&state->root->fs_info->mapping_tree,
                                      bytenr, state->metablock_size);

        for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                ret = btrfsic_map_block(state, bytenr, state->metablock_size,
                                        &block_ctx, mirror_num);
                if (ret) {
                        printk(KERN_INFO "btrfsic:"
                               " btrfsic_map_block(logical @%llu,"
                               " mirror %d) failed!\n",
                               (unsigned long long)bytenr, mirror_num);
                        continue;
                }

                if (dev_state->bdev == block_ctx.dev->bdev &&
                    dev_bytenr == block_ctx.dev_bytenr) {
                        match++;
                        btrfsic_release_block_ctx(&block_ctx);
                        break;
                }
                btrfsic_release_block_ctx(&block_ctx);
        }

        if (!match) {
                printk(KERN_INFO "btrfs: attempt to write M-block which contains logical bytenr that doesn't map to dev+physical bytenr of submit_bio,"
                       " buffer->log_bytenr=%llu, submit_bio(bdev=%s,"
                       " phys_bytenr=%llu)!\n",
                       (unsigned long long)bytenr, dev_state->name,
                       (unsigned long long)dev_bytenr);
                for (mirror_num = 1; mirror_num <= num_copies; mirror_num++) {
                        ret = btrfsic_map_block(state, bytenr,
                                                state->metablock_size,
                                                &block_ctx, mirror_num);
                        if (ret)
                                continue;

                        printk(KERN_INFO "Read logical bytenr @%llu maps to"
                               " (%s/%llu/%d)\n",
                               (unsigned long long)bytenr,
                               block_ctx.dev->name,
                               (unsigned long long)block_ctx.dev_bytenr,
                               mirror_num);
                }
                WARN_ON(1);
        }
}

static struct btrfsic_dev_state *btrfsic_dev_state_lookup(
                struct block_device *bdev)
{