// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/fs.h>
#include <linux/time.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/dax.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/namei.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include <linux/workqueue.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/iomap.h>
#include <linux/iversion.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "truncate.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
                              struct ext4_inode_info *ei)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        __u32 csum;
        __u16 dummy_csum = 0;
        int offset = offsetof(struct ext4_inode, i_checksum_lo);
        unsigned int csum_size = sizeof(dummy_csum);

        csum = ext4_chksum(sbi, ei->i_csum_seed, (__u8 *)raw, offset);
        csum = ext4_chksum(sbi, csum, (__u8 *)&dummy_csum, csum_size);
        offset += csum_size;
        csum = ext4_chksum(sbi, csum, (__u8 *)raw + offset,
                           EXT4_GOOD_OLD_INODE_SIZE - offset);

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                offset = offsetof(struct ext4_inode, i_checksum_hi);
                csum = ext4_chksum(sbi, csum, (__u8 *)raw +
                                   EXT4_GOOD_OLD_INODE_SIZE,
                                   offset - EXT4_GOOD_OLD_INODE_SIZE);
                if (EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
                        csum = ext4_chksum(sbi, csum, (__u8 *)&dummy_csum,
                                           csum_size);
                        offset += csum_size;
                }
                csum = ext4_chksum(sbi, csum, (__u8 *)raw + offset,
                                   EXT4_INODE_SIZE(inode->i_sb) - offset);
        }

        return csum;
}

static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw,
                                  struct ext4_inode_info *ei)
{
        __u32 provided, calculated;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !ext4_has_metadata_csum(inode->i_sb))
                return 1;

        provided = le16_to_cpu(raw->i_checksum_lo);
        calculated = ext4_inode_csum(inode, raw, ei);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                provided |= ((__u32)le16_to_cpu(raw->i_checksum_hi)) << 16;
        else
                calculated &= 0xFFFF;

        return provided == calculated;
}

static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
                                struct ext4_inode_info *ei)
{
        __u32 csum;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !ext4_has_metadata_csum(inode->i_sb))
                return;

        csum = ext4_inode_csum(inode, raw, ei);
        raw->i_checksum_lo = cpu_to_le16(csum & 0xFFFF);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                raw->i_checksum_hi = cpu_to_le16(csum >> 16);
}

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                              loff_t new_size)
{
        trace_ext4_begin_ordered_truncate(inode, new_size);
        /*
         * If jinode is zero, then we never opened the file for
         * writing, so there's no need to call
         * jbd2_journal_begin_ordered_truncate() since there's no
         * outstanding writes we need to flush.
         */
        if (!EXT4_I(inode)->jinode)
                return 0;
        return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
                                                   EXT4_I(inode)->jinode,
                                                   new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned int offset,
                                unsigned int length);
static int __ext4_journalled_writepage(struct page *page, unsigned int len);
static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
                                  int pextents);

/*
 * Test whether an inode is a fast symlink.
 * A fast symlink has its symlink data stored in ext4_inode_info->i_data.
 */
int ext4_inode_is_fast_symlink(struct inode *inode)
{
        if (!(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)) {
                int ea_blocks = EXT4_I(inode)->i_file_acl ?
                                EXT4_CLUSTER_SIZE(inode->i_sb) >> 9 : 0;

                if (ext4_has_inline_data(inode))
                        return 0;

                return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
        }
        return S_ISLNK(inode->i_mode) && inode->i_size &&
               (inode->i_size < EXT4_N_BLOCKS * 4);
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
                                 int nblocks)
{
        int ret;

        /*
         * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
         * moment, get_block can be called only for blocks inside i_size since
         * page cache has been already dropped and writes are blocked by
         * i_mutex. So we can safely drop the i_data_sem here.
         */
        BUG_ON(EXT4_JOURNAL(inode) == NULL);
        jbd_debug(2, "restarting handle %p\n", handle);
        up_write(&EXT4_I(inode)->i_data_sem);
        ret = ext4_journal_restart(handle, nblocks);
        down_write(&EXT4_I(inode)->i_data_sem);
        ext4_discard_preallocations(inode);

        return ret;
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_evict_inode(struct inode *inode)
{
        handle_t *handle;
        int err;
        int extra_credits = 3;
        struct ext4_xattr_inode_array *ea_inode_array = NULL;

        trace_ext4_evict_inode(inode);

        if (inode->i_nlink) {
                /*
                 * When journalling data dirty buffers are tracked only in the
                 * journal. So although mm thinks everything is clean and
                 * ready for reaping the inode might still have some pages to
                 * write in the running transaction or waiting to be
                 * checkpointed. Thus calling jbd2_journal_invalidatepage()
                 * (via truncate_inode_pages()) to discard these buffers can
                 * cause data loss. Also even if we did not discard these
                 * buffers, we would have no way to find them after the inode
                 * is reaped and thus user could see stale data if he tries to
                 * read them before the transaction is checkpointed. So be
                 * careful and force everything to disk here... We use
                 * ei->i_datasync_tid to store the newest transaction
                 * containing inode's data.
                 *
                 * Note that directories do not have this problem because they
                 * don't use page cache.
                 */
                if (inode->i_ino != EXT4_JOURNAL_INO &&
                    ext4_should_journal_data(inode) &&
                    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode)) &&
                    inode->i_data.nrpages) {
                        journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
                        tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;

                        jbd2_complete_transaction(journal, commit_tid);
                        filemap_write_and_wait(&inode->i_data);
                }
                truncate_inode_pages_final(&inode->i_data);

                goto no_delete;
        }

        if (is_bad_inode(inode))
                goto no_delete;
        dquot_initialize(inode);

        if (ext4_should_order_data(inode))
                ext4_begin_ordered_truncate(inode, 0);
        truncate_inode_pages_final(&inode->i_data);

        /*
         * Protect us against freezing - iput() caller didn't have to have any
         * protection against it
         */
        sb_start_intwrite(inode->i_sb);

        if (!IS_NOQUOTA(inode))
                extra_credits += EXT4_MAXQUOTAS_DEL_BLOCKS(inode->i_sb);

        handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE,
                                 ext4_blocks_for_truncate(inode)+extra_credits);
        if (IS_ERR(handle)) {
                ext4_std_error(inode->i_sb, PTR_ERR(handle));
                /*
                 * If we're going to skip the normal cleanup, we still need to
                 * make sure that the in-core orphan linked list is properly
                 * cleaned up.
                 */
                ext4_orphan_del(NULL, inode);
                sb_end_intwrite(inode->i_sb);
                goto no_delete;
        }

        if (IS_SYNC(inode))
                ext4_handle_sync(handle);

        /*
         * Set inode->i_size to 0 before calling ext4_truncate(). We need
         * special handling of symlinks here because i_size is used to
         * determine whether ext4_inode_info->i_data contains symlink data or
         * block mappings. Setting i_size to 0 will remove its fast symlink
         * status. Erase i_data so that it becomes a valid empty block map.
         */
        if (ext4_inode_is_fast_symlink(inode))
                memset(EXT4_I(inode)->i_data, 0, sizeof(EXT4_I(inode)->i_data));
        inode->i_size = 0;
        err = ext4_mark_inode_dirty(handle, inode);
        if (err) {
                ext4_warning(inode->i_sb,
                             "couldn't mark inode dirty (err %d)", err);
                goto stop_handle;
        }
        if (inode->i_blocks) {
                err = ext4_truncate(inode);
                if (err) {
                        ext4_error(inode->i_sb,
                                   "couldn't truncate inode %lu (err %d)",
                                   inode->i_ino, err);
                        goto stop_handle;
                }
        }

        /* Remove xattr references. */
        err = ext4_xattr_delete_inode(handle, inode, &ea_inode_array,
                                      extra_credits);
        if (err) {
                ext4_warning(inode->i_sb, "xattr delete (err %d)", err);
stop_handle:
                ext4_journal_stop(handle);
                ext4_orphan_del(NULL, inode);
                sb_end_intwrite(inode->i_sb);
                ext4_xattr_inode_array_free(ea_inode_array);
                goto no_delete;
        }

        /*
         * Kill off the orphan record which ext4_truncate created.
         * AKPM: I think this can be inside the above `if'.
         * Note that ext4_orphan_del() has to be able to cope with the
         * deletion of a non-existent orphan - this is because we don't
         * know if ext4_truncate() actually created an orphan record.
         * (Well, we could do this if we need to, but heck - it works)
         */
        ext4_orphan_del(handle, inode);
        EXT4_I(inode)->i_dtime  = get_seconds();

        /*
         * One subtle ordering requirement: if anything has gone wrong
         * (transaction abort, IO errors, whatever), then we can still
         * do these next steps (the fs will already have been marked as
         * having errors), but we can't free the inode if the mark_dirty
         * fails.
         */
        if (ext4_mark_inode_dirty(handle, inode))
                /* If that failed, just do the required in-core inode clear. */
                ext4_clear_inode(inode);
        else
                ext4_free_inode(handle, inode);
        ext4_journal_stop(handle);
        sb_end_intwrite(inode->i_sb);
        ext4_xattr_inode_array_free(ea_inode_array);
        return;
no_delete:
        ext4_clear_inode(inode);        /* We must guarantee clearing of inode... */
}

#ifdef CONFIG_QUOTA
qsize_t *ext4_get_reserved_space(struct inode *inode)
{
        return &EXT4_I(inode)->i_reserved_quota;
}
#endif

/*
 * Called with i_data_sem down, which is important since we can call
 * ext4_discard_preallocations() from here.
 */
void ext4_da_update_reserve_space(struct inode *inode,
                                        int used, int quota_claim)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        spin_lock(&ei->i_block_reservation_lock);
        trace_ext4_da_update_reserve_space(inode, used, quota_claim);
        if (unlikely(used > ei->i_reserved_data_blocks)) {
                ext4_warning(inode->i_sb, "%s: ino %lu, used %d "
                         "with only %d reserved data blocks",
                         __func__, inode->i_ino, used,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                used = ei->i_reserved_data_blocks;
        }

        /* Update per-inode reservations */
        ei->i_reserved_data_blocks -= used;
        percpu_counter_sub(&sbi->s_dirtyclusters_counter, used);

        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        /* Update quota subsystem for data blocks */
        if (quota_claim)
                dquot_claim_block(inode, EXT4_C2B(sbi, used));
        else {
                /*
                 * We did fallocate with an offset that is already delayed
                 * allocated. So on delayed allocated writeback we should
                 * not re-claim the quota for fallocated blocks.
                 */
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, used));
        }

        /*
         * If we have done all the pending block allocations and if
         * there aren't any writers on the inode, we can discard the
         * inode's preallocations.
         */
        if ((ei->i_reserved_data_blocks == 0) &&
            (atomic_read(&inode->i_writecount) == 0))
                ext4_discard_preallocations(inode);
}

static int __check_block_validity(struct inode *inode, const char *func,
                                unsigned int line,
                                struct ext4_map_blocks *map)
{
        if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), map->m_pblk,
                                   map->m_len)) {
                ext4_error_inode(inode, func, line, map->m_pblk,
                                 "lblock %lu mapped to illegal pblock "
                                 "(length %d)", (unsigned long) map->m_lblk,
                                 map->m_len);
                return -EFSCORRUPTED;
        }
        return 0;
}

int ext4_issue_zeroout(struct inode *inode, ext4_lblk_t lblk, ext4_fsblk_t pblk,
                       ext4_lblk_t len)
{
        int ret;

        if (ext4_encrypted_inode(inode))
                return fscrypt_zeroout_range(inode, lblk, pblk, len);

        ret = sb_issue_zeroout(inode->i_sb, pblk, len, GFP_NOFS);
        if (ret > 0)
                ret = 0;

        return ret;
}

#define check_block_validity(inode, map)        \
        __check_block_validity((inode), __func__, __LINE__, (map))

#ifdef ES_AGGRESSIVE_TEST
static void ext4_map_blocks_es_recheck(handle_t *handle,
                                       struct inode *inode,
                                       struct ext4_map_blocks *es_map,
                                       struct ext4_map_blocks *map,
                                       int flags)
{
        int retval;

        map->m_flags = 0;
        /*
         * There is a race window that the result is not the same.
         * e.g. xfstests #223 when dioread_nolock enables.  The reason
         * is that we lookup a block mapping in extent status tree with
         * out taking i_data_sem.  So at the time the unwritten extent
         * could be converted.
         */
        down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        }
        up_read((&EXT4_I(inode)->i_data_sem));

        /*
         * We don't check m_len because extent will be collpased in status
         * tree.  So the m_len might not equal.
         */
        if (es_map->m_lblk != map->m_lblk ||
            es_map->m_flags != map->m_flags ||
            es_map->m_pblk != map->m_pblk) {
                printk("ES cache assertion failed for inode: %lu "
                       "es_cached ex [%d/%d/%llu/%x] != "
                       "found ex [%d/%d/%llu/%x] retval %d flags %x\n",
                       inode->i_ino, es_map->m_lblk, es_map->m_len,
                       es_map->m_pblk, es_map->m_flags, map->m_lblk,
                       map->m_len, map->m_pblk, map->m_flags,
                       retval, flags);
        }
}
#endif /* ES_AGGRESSIVE_TEST */

/*
 * The ext4_map_blocks() function tries to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_map_blocks(),
 * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocated.  if
 * create==0 and the blocks are pre-allocated and unwritten, the resulting @map
 * is marked as unwritten. If the create == 1, it will mark @map as mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that case, @map is returned as unmapped but we still do fill map->m_len to
 * indicate the length of a hole starting at map->m_lblk.
 *
 * It returns the error in case of allocation failure.
 */
int ext4_map_blocks(handle_t *handle, struct inode *inode,
                    struct ext4_map_blocks *map, int flags)
{
        struct extent_status es;
        int retval;
        int ret = 0;
#ifdef ES_AGGRESSIVE_TEST
        struct ext4_map_blocks orig_map;

        memcpy(&orig_map, map, sizeof(*map));
#endif

        map->m_flags = 0;
        ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, flags, map->m_len,
                  (unsigned long) map->m_lblk);

        /*
         * ext4_map_blocks returns an int, and m_len is an unsigned int
         */
        if (unlikely(map->m_len > INT_MAX))
                map->m_len = INT_MAX;

        /* We can handle the block number less than EXT_MAX_BLOCKS */
        if (unlikely(map->m_lblk >= EXT_MAX_BLOCKS))
                return -EFSCORRUPTED;

        /* Lookup extent status tree firstly */
        if (ext4_es_lookup_extent(inode, map->m_lblk, &es)) {
                if (ext4_es_is_written(&es) || ext4_es_is_unwritten(&es)) {
                        map->m_pblk = ext4_es_pblock(&es) +
                                        map->m_lblk - es.es_lblk;
                        map->m_flags |= ext4_es_is_written(&es) ?
                                        EXT4_MAP_MAPPED : EXT4_MAP_UNWRITTEN;
                        retval = es.es_len - (map->m_lblk - es.es_lblk);
                        if (retval > map->m_len)
                                retval = map->m_len;
                        map->m_len = retval;
                } else if (ext4_es_is_delayed(&es) || ext4_es_is_hole(&es)) {
                        map->m_pblk = 0;
                        retval = es.es_len - (map->m_lblk - es.es_lblk);
                        if (retval > map->m_len)
                                retval = map->m_len;
                        map->m_len = retval;
                        retval = 0;
                } else {
                        BUG_ON(1);
                }
#ifdef ES_AGGRESSIVE_TEST
                ext4_map_blocks_es_recheck(handle, inode, map,
                                           &orig_map, flags);
#endif
                goto found;
        }

        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        }
        if (retval > 0) {
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                if (!(flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
                    !(status & EXTENT_STATUS_WRITTEN) &&
                    ext4_find_delalloc_range(inode, map->m_lblk,
                                             map->m_lblk + map->m_len - 1))
                        status |= EXTENT_STATUS_DELAYED;
                ret = ext4_es_insert_extent(inode, map->m_lblk,
                                            map->m_len, map->m_pblk, status);
                if (ret < 0)
                        retval = ret;
        }
        up_read((&EXT4_I(inode)->i_data_sem));

found:
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;
        }

        /* If it is only a block(s) look up */
        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
                return retval;

        /*
         * Returns if the blocks have already allocated
         *
         * Note that if blocks have been preallocated
         * ext4_ext_get_block() returns the create = 0
         * with buffer head unmapped.
         */
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
                /*
                 * If we need to convert extent to unwritten
                 * we continue and do the actual work in
                 * ext4_ext_map_blocks()
                 */
                if (!(flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN))
                        return retval;

        /*
         * Here we clear m_flags because after allocating an new extent,
         * it will be set again.
         */
        map->m_flags &= ~EXT4_MAP_FLAGS;

        /*
         * New blocks allocate and/or writing to unwritten extent
         * will possibly result in updating i_data, so we take
         * the write lock of i_data_sem, and call get_block()
         * with create == 1 flag.
         */
        down_write(&EXT4_I(inode)->i_data_sem);

        /*
         * We need to check for EXT4 here because migrate
         * could have changed the inode type in between
         */
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags);

                if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
                        /*
                         * We allocated new blocks which will result in
                         * i_data's format changing.  Force the migrate
                         * to fail by clearing migrate flags
                         */
                        ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
                }

                /*
                 * Update reserved blocks/metadata blocks after successful
                 * block allocation which had been deferred till now. We don't
                 * support fallocate for non extent files. So we can update
                 * reserve space here.
                 */
                if ((retval > 0) &&
                        (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
                        ext4_da_update_reserve_space(inode, retval, 1);
        }

        if (retval > 0) {
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                /*
                 * We have to zeroout blocks before inserting them into extent
                 * status tree. Otherwise someone could look them up there and
                 * use them before they are really zeroed. We also have to
                 * unmap metadata before zeroing as otherwise writeback can
                 * overwrite zeros with stale data from block device.
                 */
                if (flags & EXT4_GET_BLOCKS_ZERO &&
                    map->m_flags & EXT4_MAP_MAPPED &&
                    map->m_flags & EXT4_MAP_NEW) {
                        clean_bdev_aliases(inode->i_sb->s_bdev, map->m_pblk,
                                           map->m_len);
                        ret = ext4_issue_zeroout(inode, map->m_lblk,
                                                 map->m_pblk, map->m_len);
                        if (ret) {
                                retval = ret;
                                goto out_sem;
                        }
                }

                /*
                 * If the extent has been zeroed out, we don't need to update
                 * extent status tree.
                 */
                if ((flags & EXT4_GET_BLOCKS_PRE_IO) &&
                    ext4_es_lookup_extent(inode, map->m_lblk, &es)) {
                        if (ext4_es_is_written(&es))
                                goto out_sem;
                }
                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                if (!(flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
                    !(status & EXTENT_STATUS_WRITTEN) &&
                    ext4_find_delalloc_range(inode, map->m_lblk,
                                             map->m_lblk + map->m_len - 1))
                        status |= EXTENT_STATUS_DELAYED;
                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            map->m_pblk, status);
                if (ret < 0) {
                        retval = ret;
                        goto out_sem;
                }
        }

out_sem:
        up_write((&EXT4_I(inode)->i_data_sem));
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;

                /*
                 * Inodes with freshly allocated blocks where contents will be
                 * visible after transaction commit must be on transaction's
                 * ordered data list.
                 */
                if (map->m_flags & EXT4_MAP_NEW &&
                    !(map->m_flags & EXT4_MAP_UNWRITTEN) &&
                    !(flags & EXT4_GET_BLOCKS_ZERO) &&
                    !ext4_is_quota_file(inode) &&
                    ext4_should_order_data(inode)) {
                        if (flags & EXT4_GET_BLOCKS_IO_SUBMIT)
                                ret = ext4_jbd2_inode_add_wait(handle, inode);
                        else
                                ret = ext4_jbd2_inode_add_write(handle, inode);
                        if (ret)
                                return ret;
                }
        }
        return retval;
}

/*
 * Update EXT4_MAP_FLAGS in bh->b_state. For buffer heads attached to pages
 * we have to be careful as someone else may be manipulating b_state as well.
 */
static void ext4_update_bh_state(struct buffer_head *bh, unsigned long flags)
{
        unsigned long old_state;
        unsigned long new_state;

        flags &= EXT4_MAP_FLAGS;

        /* Dummy buffer_head? Set non-atomically. */
        if (!bh->b_page) {
                bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | flags;
                return;
        }
        /*
         * Someone else may be modifying b_state. Be careful! This is ugly but
         * once we get rid of using bh as a container for mapping information
         * to pass to / from get_block functions, this can go away.
         */
        do {
                old_state = READ_ONCE(bh->b_state);
                new_state = (old_state & ~EXT4_MAP_FLAGS) | flags;
        } while (unlikely(
                 cmpxchg(&bh->b_state, old_state, new_state) != old_state));
}

static int _ext4_get_block(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int flags)
{
        struct ext4_map_blocks map;
        int ret = 0;

        if (ext4_has_inline_data(inode))
                return -ERANGE;

        map.m_lblk = iblock;
        map.m_len = bh->b_size >> inode->i_blkbits;

        ret = ext4_map_blocks(ext4_journal_current_handle(), inode, &map,
                              flags);
        if (ret > 0) {
                map_bh(bh, inode->i_sb, map.m_pblk);
                ext4_update_bh_state(bh, map.m_flags);
                bh->b_size = inode->i_sb->s_blocksize * map.m_len;
                ret = 0;
        } else if (ret == 0) {
                /* hole case, need to fill in bh->b_size */
                bh->b_size = inode->i_sb->s_blocksize * map.m_len;
        }
        return ret;
}

int ext4_get_block(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh, int create)
{
        return _ext4_get_block(inode, iblock, bh,
                               create ? EXT4_GET_BLOCKS_CREATE : 0);
}

/*
 * Get block function used when preparing for buffered write if we require
 * creating an unwritten extent if blocks haven't been allocated.  The extent
 * will be converted to written after the IO is complete.
 */
int ext4_get_block_unwritten(struct inode *inode, sector_t iblock,
                             struct buffer_head *bh_result, int create)
{
        ext4_debug("ext4_get_block_unwritten: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        return _ext4_get_block(inode, iblock, bh_result,
                               EXT4_GET_BLOCKS_IO_CREATE_EXT);
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

/*
 * Get blocks function for the cases that need to start a transaction -
 * generally difference cases of direct IO and DAX IO. It also handles retries
 * in case of ENOSPC.
 */
static int ext4_get_block_trans(struct inode *inode, sector_t iblock,
                                struct buffer_head *bh_result, int flags)
{
        int dio_credits;
        handle_t *handle;
        int retries = 0;
        int ret;

        /* Trim mapping request to maximum we can map at once for DIO */
        if (bh_result->b_size >> inode->i_blkbits > DIO_MAX_BLOCKS)
                bh_result->b_size = DIO_MAX_BLOCKS << inode->i_blkbits;
        dio_credits = ext4_chunk_trans_blocks(inode,
                                      bh_result->b_size >> inode->i_blkbits);
retry:
        handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, dio_credits);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        ret = _ext4_get_block(inode, iblock, bh_result, flags);
        ext4_journal_stop(handle);

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;
        return ret;
}

/* Get block function for DIO reads and writes to inodes without extents */
int ext4_dio_get_block(struct inode *inode, sector_t iblock,
                       struct buffer_head *bh, int create)
{
        /* We don't expect handle for direct IO */
        WARN_ON_ONCE(ext4_journal_current_handle());

        if (!create)
                return _ext4_get_block(inode, iblock, bh, 0);
        return ext4_get_block_trans(inode, iblock, bh, EXT4_GET_BLOCKS_CREATE);
}

/*
 * Get block function for AIO DIO writes when we create unwritten extent if
 * blocks are not allocated yet. The extent will be converted to written
 * after IO is complete.
 */
static int ext4_dio_get_block_unwritten_async(struct inode *inode,
                sector_t iblock, struct buffer_head *bh_result, int create)
{
        int ret;

        /* We don't expect handle for direct IO */
        WARN_ON_ONCE(ext4_journal_current_handle());

        ret = ext4_get_block_trans(inode, iblock, bh_result,
                                   EXT4_GET_BLOCKS_IO_CREATE_EXT);

        /*
         * When doing DIO using unwritten extents, we need io_end to convert
         * unwritten extents to written on IO completion. We allocate io_end
         * once we spot unwritten extent and store it in b_private. Generic
         * DIO code keeps b_private set and furthermore passes the value to
         * our completion callback in 'private' argument.
         */
        if (!ret && buffer_unwritten(bh_result)) {
                if (!bh_result->b_private) {
                        ext4_io_end_t *io_end;

                        io_end = ext4_init_io_end(inode, GFP_KERNEL);
                        if (!io_end)
                                return -ENOMEM;
                        bh_result->b_private = io_end;
                        ext4_set_io_unwritten_flag(inode, io_end);
                }
                set_buffer_defer_completion(bh_result);
        }

        return ret;
}

/*
 * Get block function for non-AIO DIO writes when we create unwritten extent if
 * blocks are not allocated yet. The extent will be converted to written
 * after IO is complete by ext4_direct_IO_write().
 */
static int ext4_dio_get_block_unwritten_sync(struct inode *inode,
                sector_t iblock, struct buffer_head *bh_result, int create)
{
        int ret;

        /* We don't expect handle for direct IO */
        WARN_ON_ONCE(ext4_journal_current_handle());

        ret = ext4_get_block_trans(inode, iblock, bh_result,
                                   EXT4_GET_BLOCKS_IO_CREATE_EXT);

        /*
         * Mark inode as having pending DIO writes to unwritten extents.
         * ext4_direct_IO_write() checks this flag and converts extents to
         * written.
         */
        if (!ret && buffer_unwritten(bh_result))
                ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);

        return ret;
}

static int ext4_dio_get_block_overwrite(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
        int ret;

        ext4_debug("ext4_dio_get_block_overwrite: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        /* We don't expect handle for direct IO */
        WARN_ON_ONCE(ext4_journal_current_handle());

        ret = _ext4_get_block(inode, iblock, bh_result, 0);
        /*
         * Blocks should have been preallocated! ext4_file_write_iter() checks
         * that.
         */
        WARN_ON_ONCE(!buffer_mapped(bh_result) || buffer_unwritten(bh_result));

        return ret;
}


/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                                ext4_lblk_t block, int map_flags)
{
        struct ext4_map_blocks map;
        struct buffer_head *bh;
        int create = map_flags & EXT4_GET_BLOCKS_CREATE;
        int err;

        J_ASSERT(handle != NULL || create == 0);

        map.m_lblk = block;
        map.m_len = 1;
        err = ext4_map_blocks(handle, inode, &map, map_flags);

        if (err == 0)
                return create ? ERR_PTR(-ENOSPC) : NULL;
        if (err < 0)
                return ERR_PTR(err);

        bh = sb_getblk(inode->i_sb, map.m_pblk);
        if (unlikely(!bh))
                return ERR_PTR(-ENOMEM);
        if (map.m_flags & EXT4_MAP_NEW) {
                J_ASSERT(create != 0);
                J_ASSERT(handle != NULL);

                /*
                 * Now that we do not always journal data, we should
                 * keep in mind whether this should always journal the
                 * new buffer as metadata.  For now, regular file
                 * writes use ext4_get_block instead, so it's not a
                 * problem.
                 */
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                err = ext4_journal_get_create_access(handle, bh);
                if (unlikely(err)) {
                        unlock_buffer(bh);
                        goto errout;
                }
                if (!buffer_uptodate(bh)) {
                        memset(bh->b_data, 0, inode->i_sb->s_blocksize);
                        set_buffer_uptodate(bh);
                }
                unlock_buffer(bh);
                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, bh);

                if (unlikely(err))
                        goto errout;
        } else
                BUFFER_TRACE(bh, "not a new buffer");
        return bh;
errout:
        brelse(bh);
        return ERR_PTR(err);
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                               ext4_lblk_t block, int map_flags)
{
        struct buffer_head *bh;

        bh = ext4_getblk(handle, inode, block, map_flags);
        if (IS_ERR(bh))
                return bh;
        if (!bh || buffer_uptodate(bh))
                return bh;
        ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1, &bh);
        wait_on_buffer(bh);
        if (buffer_uptodate(bh))
                return bh;
        put_bh(bh);
        return ERR_PTR(-EIO);
}

/* Read a contiguous batch of blocks. */
int ext4_bread_batch(struct inode *inode, ext4_lblk_t block, int bh_count,
                     bool wait, struct buffer_head **bhs)
{
        int i, err;

        for (i = 0; i < bh_count; i++) {
                bhs[i] = ext4_getblk(NULL, inode, block + i, 0 /* map_flags */);
                if (IS_ERR(bhs[i])) {
                        err = PTR_ERR(bhs[i]);
                        bh_count = i;
                        goto out_brelse;
                }
        }

        for (i = 0; i < bh_count; i++)
                /* Note that NULL bhs[i] is valid because of holes. */
                if (bhs[i] && !buffer_uptodate(bhs[i]))
                        ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1,
                                    &bhs[i]);

        if (!wait)
                return 0;

        for (i = 0; i < bh_count; i++)
                if (bhs[i])
                        wait_on_buffer(bhs[i]);

        for (i = 0; i < bh_count; i++) {
                if (bhs[i] && !buffer_uptodate(bhs[i])) {
                        err = -EIO;
                        goto out_brelse;
                }
        }
        return 0;

out_brelse:
        for (i = 0; i < bh_count; i++) {
                brelse(bhs[i]);
                bhs[i] = NULL;
        }
        return err;
}

int ext4_walk_page_buffers(handle_t *handle,
                           struct buffer_head *head,
                           unsigned from,
                           unsigned to,
                           int *partial,
                           int (*fn)(handle_t *handle,
                                     struct buffer_head *bh))
{
        struct buffer_head *bh;
        unsigned block_start, block_end;
        unsigned blocksize = head->b_size;
        int err, ret = 0;
        struct buffer_head *next;

        for (bh = head, block_start = 0;
             ret == 0 && (bh != head || !block_start);
             block_start = block_end, bh = next) {
                next = bh->b_this_page;
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (partial && !buffer_uptodate(bh))
                                *partial = 1;
                        continue;
                }
                err = (*fn)(handle, bh);
                if (!ret)
                        ret = err;
        }
        return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage().  In that case, we
 * *know* that ext4_writepage() has generated enough buffer credits to do the
 * whole page.  So we won't block on the journal in that case, which is good,
 * because the caller may be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
int do_journal_get_write_access(handle_t *handle,
                                struct buffer_head *bh)
{
        int dirty = buffer_dirty(bh);
        int ret;

        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        /*
         * __block_write_begin() could have dirtied some buffers. Clean
         * the dirty bit as jbd2_journal_get_write_access() could complain
         * otherwise about fs integrity issues. Setting of the dirty bit
         * by __block_write_begin() isn't a real problem here as we clear
         * the bit before releasing a page lock and thus writeback cannot
         * ever write the buffer.
         */
        if (dirty)
                clear_buffer_dirty(bh);
        BUFFER_TRACE(bh, "get write access");
        ret = ext4_journal_get_write_access(handle, bh);
        if (!ret && dirty)
                ret = ext4_handle_dirty_metadata(handle, NULL, bh);
        return ret;
}

#ifdef CONFIG_EXT4_FS_ENCRYPTION
static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
                                  get_block_t *get_block)
{
        unsigned from = pos & (PAGE_SIZE - 1);
        unsigned to = from + len;
        struct inode *inode = page->mapping->host;
        unsigned block_start, block_end;
        sector_t block;
        int err = 0;
        unsigned blocksize = inode->i_sb->s_blocksize;
        unsigned bbits;
        struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
        bool decrypt = false;

        BUG_ON(!PageLocked(page));
        BUG_ON(from > PAGE_SIZE);
        BUG_ON(to > PAGE_SIZE);
        BUG_ON(from > to);

        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);
        head = page_buffers(page);
        bbits = ilog2(blocksize);
        block = (sector_t)page->index << (PAGE_SHIFT - bbits);

        for (bh = head, block_start = 0; bh != head || !block_start;
            block++, block_start = block_end, bh = bh->b_this_page) {
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (PageUptodate(page)) {
                                if (!buffer_uptodate(bh))
                                        set_buffer_uptodate(bh);
                        }
                        continue;
                }
                if (buffer_new(bh))
                        clear_buffer_new(bh);
                if (!buffer_mapped(bh)) {
                        WARN_ON(bh->b_size != blocksize);
                        err = get_block(inode, block, bh, 1);
                        if (err)
                                break;
                        if (buffer_new(bh)) {
                                clean_bdev_bh_alias(bh);
                                if (PageUptodate(page)) {
                                        clear_buffer_new(bh);
                                        set_buffer_uptodate(bh);
                                        mark_buffer_dirty(bh);
                                        continue;
                                }
                                if (block_end > to || block_start < from)
                                        zero_user_segments(page, to, block_end,
                                                           block_start, from);
                                continue;
                        }
                }
                if (PageUptodate(page)) {
                        if (!buffer_uptodate(bh))
                                set_buffer_uptodate(bh);
                        continue;
                }
                if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
                    !buffer_unwritten(bh) &&
                    (block_start < from || block_end > to)) {
                        ll_rw_block(REQ_OP_READ, 0, 1, &bh);
                        *wait_bh++ = bh;
                        decrypt = ext4_encrypted_inode(inode) &&
                                S_ISREG(inode->i_mode);
                }
        }
        /*
         * If we issued read requests, let them complete.
         */
        while (wait_bh > wait) {
                wait_on_buffer(*--wait_bh);
                if (!buffer_uptodate(*wait_bh))
                        err = -EIO;
        }
        if (unlikely(err))
                page_zero_new_buffers(page, from, to);
        else if (decrypt)
                err = fscrypt_decrypt_page(page->mapping->host, page,
                                PAGE_SIZE, 0, page->index);
        return err;
}
#endif

static int ext4_write_begin(struct file *file, struct address_space *mapping,
                            loff_t pos, unsigned len, unsigned flags,
                            struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        int ret, needed_blocks;
        handle_t *handle;
        int retries = 0;
        struct page *page;
        pgoff_t index;
        unsigned from, to;

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

        trace_ext4_write_begin(inode, pos, len, flags);
        /*
         * Reserve one block more for addition to orphan list in case
         * we allocate blocks but write fails for some reason
         */
        needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
        index = pos >> PAGE_SHIFT;
        from = pos & (PAGE_SIZE - 1);
        to = from + len;

        if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
                ret = ext4_try_to_write_inline_data(mapping, inode, pos, len,
                                                    flags, pagep);
                if (ret < 0)
                        return ret;
                if (ret == 1)
                        return 0;
        }

        /*
         * grab_cache_page_write_begin() can take a long time if the
         * system is thrashing due to memory pressure, or if the page
         * is being written back.  So grab it first before we start
         * the transaction handle.  This also allows us to allocate
         * the page (if needed) without using GFP_NOFS.
         */
retry_grab:
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;
        unlock_page(page);

retry_journal:
        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
        if (IS_ERR(handle)) {
                put_page(page);
                return PTR_ERR(handle);
        }

        lock_page(page);
        if (page->mapping != mapping) {
                /* The page got truncated from under us */
                unlock_page(page);
                put_page(page);
                ext4_journal_stop(handle);
                goto retry_grab;
        }
        /* In case writeback began while the page was unlocked */
        wait_for_stable_page(page);

#ifdef CONFIG_EXT4_FS_ENCRYPTION
        if (ext4_should_dioread_nolock(inode))
                ret = ext4_block_write_begin(page, pos, len,
                                             ext4_get_block_unwritten);
        else
                ret = ext4_block_write_begin(page, pos, len,
                                             ext4_get_block);
#else
        if (ext4_should_dioread_nolock(inode))
                ret = __block_write_begin(page, pos, len,
                                          ext4_get_block_unwritten);
        else
                ret = __block_write_begin(page, pos, len, ext4_get_block);
#endif
        if (!ret && ext4_should_journal_data(inode)) {
                ret = ext4_walk_page_buffers(handle, page_buffers(page),
                                             from, to, NULL,
                                             do_journal_get_write_access);
        }

        if (ret) {
                unlock_page(page);
                /*
                 * __block_write_begin may have instantiated a few blocks
                 * outside i_size.  Trim these off again. Don't need
                 * i_size_read because we hold i_mutex.
                 *
                 * Add inode to orphan list in case we crash before
                 * truncate finishes
                 */
                if (pos + len > inode->i_size && ext4_can_truncate(inode))
                        ext4_orphan_add(handle, inode);

                ext4_journal_stop(handle);
                if (pos + len > inode->i_size) {
                        ext4_truncate_failed_write(inode);
                        /*
                         * If truncate failed early the inode might
                         * still be on the orphan list; we need to
                         * make sure the inode is removed from the
                         * orphan list in that case.
                         */
                        if (inode->i_nlink)
                                ext4_orphan_del(NULL, inode);
                }

                if (ret == -ENOSPC &&
                    ext4_should_retry_alloc(inode->i_sb, &retries))
                        goto retry_journal;
                put_page(page);
                return ret;
        }
        *pagep = page;
        return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
        int ret;
        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        set_buffer_uptodate(bh);
        ret = ext4_handle_dirty_metadata(handle, NULL, bh);
        clear_buffer_meta(bh);
        clear_buffer_prio(bh);
        return ret;
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_write_end(struct file *file,
                          struct address_space *mapping,
                          loff_t pos, unsigned len, unsigned copied,
                          struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        loff_t old_size = inode->i_size;
        int ret = 0, ret2;
        int i_size_changed = 0;

        trace_ext4_write_end(inode, pos, len, copied);
        if (ext4_has_inline_data(inode)) {
                ret = ext4_write_inline_data_end(inode, pos, len,
                                                 copied, page);
                if (ret < 0) {
                        unlock_page(page);
                        put_page(page);
                        goto errout;
                }
                copied = ret;
        } else
                copied = block_write_end(file, mapping, pos,
                                         len, copied, page, fsdata);
        /*
         * it's important to update i_size while still holding page lock:
         * page writeout could otherwise come in and zero beyond i_size.
         */
        i_size_changed = ext4_update_inode_size(inode, pos + copied);
        unlock_page(page);
        put_page(page);

        if (old_size < pos)
                pagecache_isize_extended(inode, old_size, pos);
        /*
         * Don't mark the inode dirty under page lock. First, it unnecessarily
         * makes the holding time of page lock longer. Second, it forces lock
         * ordering of page lock and transaction start for journaling
         * filesystems.
         */
        if (i_size_changed)
                ext4_mark_inode_dirty(handle, inode);

        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);
errout:
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

/*
 * This is a private version of page_zero_new_buffers() which doesn't
 * set the buffer to be dirty, since in data=journalled mode we need
 * to call ext4_handle_dirty_metadata() instead.
 */
static void ext4_journalled_zero_new_buffers(handle_t *handle,
                                            struct page *page,
                                            unsigned from, unsigned to)
{
        unsigned int block_start = 0, block_end;
        struct buffer_head *head, *bh;

        bh = head = page_buffers(page);
        do {
                block_end = block_start + bh->b_size;
                if (buffer_new(bh)) {
                        if (block_end > from && block_start < to) {
                                if (!PageUptodate(page)) {
                                        unsigned start, size;

                                        start = max(from, block_start);
                                        size = min(to, block_end) - start;

                                        zero_user(page, start, size);
                                        write_end_fn(handle, bh);
                                }
                                clear_buffer_new(bh);
                        }
                }
                block_start = block_end;
                bh = bh->b_this_page;
        } while (bh != head);
}

static int ext4_journalled_write_end(struct file *file,
                                     struct address_space *mapping,
                                     loff_t pos, unsigned len, unsigned copied,
                                     struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        loff_t old_size = inode->i_size;
        int ret = 0, ret2;
        int partial = 0;
        unsigned from, to;
        int size_changed = 0;

        trace_ext4_journalled_write_end(inode, pos, len, copied);
        from = pos & (PAGE_SIZE - 1);
        to = from + len;

        BUG_ON(!ext4_handle_valid(handle));

        if (ext4_has_inline_data(inode)) {
                ret = ext4_write_inline_data_end(inode, pos, len,
                                                 copied, page);
                if (ret < 0) {
                        unlock_page(page);
                        put_page(page);
                        goto errout;
                }
                copied = ret;
        } else if (unlikely(copied < len) && !PageUptodate(page)) {
                copied = 0;
                ext4_journalled_zero_new_buffers(handle, page, from, to);
        } else {
                if (unlikely(copied < len))
                        ext4_journalled_zero_new_buffers(handle, page,
                                                         from + copied, to);
                ret = ext4_walk_page_buffers(handle, page_buffers(page), from,
                                             from + copied, &partial,
                                             write_end_fn);
                if (!partial)
                        SetPageUptodate(page);
        }
        size_changed = ext4_update_inode_size(inode, pos + copied);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        unlock_page(page);
        put_page(page);

        if (old_size < pos)
                pagecache_isize_extended(inode, old_size, pos);

        if (size_changed) {
                ret2 = ext4_mark_inode_dirty(handle, inode);
                if (!ret)
                        ret = ret2;
        }

        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);

errout:
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;
        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

/*
 * Reserve space for a single cluster
 */
static int ext4_da_reserve_space(struct inode *inode)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);
        int ret;

        /*
         * We will charge metadata quota at writeout time; this saves
         * us from metadata over-estimation, though we may go over by
         * a small amount in the end.  Here we just reserve for data.
         */
        ret = dquot_reserve_block(inode, EXT4_C2B(sbi, 1));
        if (ret)
                return ret;

        spin_lock(&ei->i_block_reservation_lock);
        if (ext4_claim_free_clusters(sbi, 1, 0)) {
                spin_unlock(&ei->i_block_reservation_lock);
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
                return -ENOSPC;
        }
        ei->i_reserved_data_blocks++;
        trace_ext4_da_reserve_space(inode);
        spin_unlock(&ei->i_block_reservation_lock);

        return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        if (!to_free)
                return;         /* Nothing to release, exit */

        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

        trace_ext4_da_release_space(inode, to_free);
        if (unlikely(to_free > ei->i_reserved_data_blocks)) {
                /*
                 * if there aren't enough reserved blocks, then the
                 * counter is messed up somewhere.  Since this
                 * function is called from invalidate page, it's
                 * harmless to return without any action.
                 */
                ext4_warning(inode->i_sb, "ext4_da_release_space: "
                         "ino %lu, to_free %d with only %d reserved "
                         "data blocks", inode->i_ino, to_free,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                to_free = ei->i_reserved_data_blocks;
        }
        ei->i_reserved_data_blocks -= to_free;

        /* update fs dirty data blocks counter */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter, to_free);

        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
}

static void ext4_da_page_release_reservation(struct page *page,
                                             unsigned int offset,
                                             unsigned int length)
{
        int to_release = 0, contiguous_blks = 0;
        struct buffer_head *head, *bh;
        unsigned int curr_off = 0;
        struct inode *inode = page->mapping->host;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        unsigned int stop = offset + length;
        int num_clusters;
        ext4_fsblk_t lblk;

        BUG_ON(stop > PAGE_SIZE || stop < length);

        head = page_buffers(page);
        bh = head;
        do {
                unsigned int next_off = curr_off + bh->b_size;

                if (next_off > stop)
                        break;

                if ((offset <= curr_off) && (buffer_delay(bh))) {
                        to_release++;
                        contiguous_blks++;
                        clear_buffer_delay(bh);
                } else if (contiguous_blks) {
                        lblk = page->index <<
                               (PAGE_SHIFT - inode->i_blkbits);
                        lblk += (curr_off >> inode->i_blkbits) -
                                contiguous_blks;
                        ext4_es_remove_extent(inode, lblk, contiguous_blks);
                        contiguous_blks = 0;
                }
                curr_off = next_off;
        } while ((bh = bh->b_this_page) != head);

        if (contiguous_blks) {
                lblk = page->index << (PAGE_SHIFT - inode->i_blkbits);
                lblk += (curr_off >> inode->i_blkbits) - contiguous_blks;
                ext4_es_remove_extent(inode, lblk, contiguous_blks);
        }

        /* If we have released all the blocks belonging to a cluster, then we
         * need to release the reserved space for that cluster. */
        num_clusters = EXT4_NUM_B2C(sbi, to_release);
        while (num_clusters > 0) {
                lblk = (page->index << (PAGE_SHIFT - inode->i_blkbits)) +
                        ((num_clusters - 1) << sbi->s_cluster_bits);
                if (sbi->s_cluster_ratio == 1 ||
                    !ext4_find_delalloc_cluster(inode, lblk))
                        ext4_da_release_space(inode, 1);

                num_clusters--;
        }
}

/*
 * Delayed allocation stuff
 */

struct mpage_da_data {
        struct inode *inode;
        struct writeback_control *wbc;

        pgoff_t first_page;     /* The first page to write */
        pgoff_t next_page;      /* Current page to examine */
        pgoff_t last_page;      /* Last page to examine */
        /*
         * Extent to map - this can be after first_page because that can be
         * fully mapped. We somewhat abuse m_flags to store whether the extent
         * is delalloc or unwritten.
         */
        struct ext4_map_blocks map;
        struct ext4_io_submit io_submit;        /* IO submission data */
        unsigned int do_map:1;
};

static void mpage_release_unused_pages(struct mpage_da_data *mpd,
                                       bool invalidate)
{
        int nr_pages, i;
        pgoff_t index, end;
        struct pagevec pvec;
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;

        /* This is necessary when next_page == 0. */
        if (mpd->first_page >= mpd->next_page)
                return;

        index = mpd->first_page;
        end   = mpd->next_page - 1;
        if (invalidate) {
                ext4_lblk_t start, last;
                start = index << (PAGE_SHIFT - inode->i_blkbits);
                last = end << (PAGE_SHIFT - inode->i_blkbits);
                ext4_es_remove_extent(inode, start, last - start + 1);
        }

        pagevec_init(&pvec);
        while (index <= end) {
                nr_pages = pagevec_lookup_range(&pvec, mapping, &index, end);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        BUG_ON(!PageLocked(page));
                        BUG_ON(PageWriteback(page));
                        if (invalidate) {
                                if (page_mapped(page))
                                        clear_page_dirty_for_io(page);
                                block_invalidatepage(page, 0, PAGE_SIZE);
                                ClearPageUptodate(page);
                        }
                        unlock_page(page);
                }
                pagevec_release(&pvec);
        }
}

static void ext4_print_free_blocks(struct inode *inode)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct super_block *sb = inode->i_sb;
        struct ext4_inode_info *ei = EXT4_I(inode);

        ext4_msg(sb, KERN_CRIT, "Total free blocks count %lld",
               EXT4_C2B(EXT4_SB(inode->i_sb),
                        ext4_count_free_clusters(sb)));
        ext4_msg(sb, KERN_CRIT, "Free/Dirty block details");
        ext4_msg(sb, KERN_CRIT, "free_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(sb),
                percpu_counter_sum(&sbi->s_freeclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "dirty_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(sb),
                percpu_counter_sum(&sbi->s_dirtyclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "Block reservation details");
        ext4_msg(sb, KERN_CRIT, "i_reserved_data_blocks=%u",
                 ei->i_reserved_data_blocks);
        return;
}

static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
        return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}

/*
 * This function is grabs code from the very beginning of
 * ext4_map_blocks, but assumes that the caller is from delayed write
 * time. This function looks up the requested blocks and sets the
 * buffer delay bit under the protection of i_data_sem.
 */
static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
                              struct ext4_map_blocks *map,
                              struct buffer_head *bh)
{
        struct extent_status es;
        int retval;
        sector_t invalid_block = ~((sector_t) 0xffff);
#ifdef ES_AGGRESSIVE_TEST
        struct ext4_map_blocks orig_map;

        memcpy(&orig_map, map, sizeof(*map));
#endif

        if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
                invalid_block = ~0;

        map->m_flags = 0;
        ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, map->m_len,
                  (unsigned long) map->m_lblk);

        /* Lookup extent status tree firstly */
        if (ext4_es_lookup_extent(inode, iblock, &es)) {
                if (ext4_es_is_hole(&es)) {
                        retval = 0;
                        down_read(&EXT4_I(inode)->i_data_sem);
                        goto add_delayed;
                }

                /*
                 * Delayed extent could be allocated by fallocate.
                 * So we need to check it.
                 */
                if (ext4_es_is_delayed(&es) && !ext4_es_is_unwritten(&es)) {
                        map_bh(bh, inode->i_sb, invalid_block);
                        set_buffer_new(bh);
                        set_buffer_delay(bh);
                        return 0;
                }

                map->m_pblk = ext4_es_pblock(&es) + iblock - es.es_lblk;
                retval = es.es_len - (iblock - es.es_lblk);
                if (retval > map->m_len)
                        retval = map->m_len;
                map->m_len = retval;
                if (ext4_es_is_written(&es))
                        map->m_flags |= EXT4_MAP_MAPPED;
                else if (ext4_es_is_unwritten(&es))
                        map->m_flags |= EXT4_MAP_UNWRITTEN;
                else
                        BUG_ON(1);

#ifdef ES_AGGRESSIVE_TEST
                ext4_map_blocks_es_recheck(NULL, inode, map, &orig_map, 0);
#endif
                return retval;
        }

        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_has_inline_data(inode))
                retval = 0;
        else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                retval = ext4_ext_map_blocks(NULL, inode, map, 0);
        else
                retval = ext4_ind_map_blocks(NULL, inode, map, 0);

add_delayed:
        if (retval == 0) {
                int ret;
                /*
                 * XXX: __block_prepare_write() unmaps passed block,
                 * is it OK?
                 */
                /*
                 * If the block was allocated from previously allocated cluster,
                 * then we don't need to reserve it again. However we still need
                 * to reserve metadata for every block we're going to write.
                 */
                if (EXT4_SB(inode->i_sb)->s_cluster_ratio == 1 ||
                    !ext4_find_delalloc_cluster(inode, map->m_lblk)) {
                        ret = ext4_da_reserve_space(inode);
                        if (ret) {
                                /* not enough space to reserve */
                                retval = ret;
                                goto out_unlock;
                        }
                }

                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            ~0, EXTENT_STATUS_DELAYED);
                if (ret) {
                        retval = ret;
                        goto out_unlock;
                }

                map_bh(bh, inode->i_sb, invalid_block);
                set_buffer_new(bh);
                set_buffer_delay(bh);
        } else if (retval > 0) {
                int ret;
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            map->m_pblk, status);
                if (ret != 0)
                        retval = ret;
        }

out_unlock:
        up_read((&EXT4_I(inode)->i_data_sem));

        return retval;
}

/*
 * This is a special get_block_t callback which is used by
 * ext4_da_write_begin().  It will either return mapped block or
 * reserve space for a single block.
 *
 * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
 * We also have b_blocknr = -1 and b_bdev initialized properly
 *
 * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
 * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
 * initialized properly.
 */
int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int create)
{
        struct ext4_map_blocks map;
        int ret = 0;

        BUG_ON(create == 0);
        BUG_ON(bh->b_size != inode->i_sb->s_blocksize);

        map.m_lblk = iblock;
        map.m_len = 1;

        /*
         * first, we need to know whether the block is allocated already
         * preallocated blocks are unmapped but should treated
         * the same as allocated blocks.
         */
        ret = ext4_da_map_blocks(inode, iblock, &map, bh);
        if (ret <= 0)
                return ret;

        map_bh(bh, inode->i_sb, map.m_pblk);
        ext4_update_bh_state(bh, map.m_flags);

        if (buffer_unwritten(bh)) {
                /* A delayed write to unwritten bh should be marked
                 * new and mapped.  Mapped ensures that we don't do
                 * get_block multiple times when we write to the same
                 * offset and new ensures that we do proper zero out
                 * for partial write.
                 */
                set_buffer_new(bh);
                set_buffer_mapped(bh);
        }
        return 0;
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
        get_bh(bh);
        return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
        put_bh(bh);
        return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                                       unsigned int len)
{
        struct address_space *mapping = page->mapping;
        struct inode *inode = mapping->host;
        struct buffer_head *page_bufs = NULL;
        handle_t *handle = NULL;
        int ret = 0, err = 0;
        int inline_data = ext4_has_inline_data(inode);
        struct buffer_head *inode_bh = NULL;

        ClearPageChecked(page);

        if (inline_data) {
                BUG_ON(page->index != 0);
                BUG_ON(len > ext4_get_max_inline_size(inode));
                inode_bh = ext4_journalled_write_inline_data(inode, len, page);
                if (inode_bh == NULL)
                        goto out;
        } else {
                page_bufs = page_buffers(page);
                if (!page_bufs) {
                        BUG();
                        goto out;
                }

                ext4_walk_page_buffers(handle, page_bufs, 0, len,
                                       NULL, bget_one);
        }
        /*
         * We need to release the page lock before we start the
         * journal, so grab a reference so the page won't disappear
         * out from under us.
         */
        get_page(page);
        unlock_page(page);

        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
                                    ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                put_page(page);
                goto out_no_pagelock;
        }
        BUG_ON(!ext4_handle_valid(handle));

        lock_page(page);
        put_page(page);
        if (page->mapping != mapping) {
                /* The page got truncated from under us */
                ext4_journal_stop(handle);
                ret = 0;
                goto out;
        }

        if (inline_data) {
                BUFFER_TRACE(inode_bh, "get write access");
                ret = ext4_journal_get_write_access(handle, inode_bh);

                err = ext4_handle_dirty_metadata(handle, inode, inode_bh);

        } else {
                ret = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             do_journal_get_write_access);

                err = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             write_end_fn);
        }
        if (ret == 0)
                ret = err;
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        err = ext4_journal_stop(handle);
        if (!ret)
                ret = err;

        if (!ext4_has_inline_data(inode))
                ext4_walk_page_buffers(NULL, page_bufs, 0, len,
                                       NULL, bput_one);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
out:
        unlock_page(page);
out_no_pagelock:
        brelse(inode_bh);
        return ret;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), no one guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * This function can get called via...
 *   - ext4_writepages after taking page lock (have journal handle)
 *   - journal_submit_inode_data_buffers (no journal handle)
 *   - shrink_page_list via the kswapd/direct reclaim (no journal handle)
 *   - grab_page_cache when doing write_begin (have journal handle)
 *
 * We don't do any block allocation in this function. If we have page with
 * multiple blocks we need to write those buffer_heads that are mapped. This
 * is important for mmaped based write. So if we do with blocksize 1K
 * truncate(f, 1024);
 * a = mmap(f, 0, 4096);
 * a[0] = 'a';
 * truncate(f, 4096);
 * we have in the page first buffer_head mapped via page_mkwrite call back
 * but other buffer_heads would be unmapped but dirty (dirty done via the
 * do_wp_page). So writepage should write the first block. If we modify
 * the mmap area beyond 1024 we will again get a page_fault and the
 * page_mkwrite callback will do the block allocation and mark the
 * buffer_heads mapped.
 *
 * We redirty the page if we have any buffer_heads that is either delay or
 * unwritten in the page.
 *
 * We can get recursively called as show below.
 *
 *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *              ext4_writepage()
 *
 * But since we don't do any block allocation we should not deadlock.
 * Page also have the dirty flag cleared so we don't get recurive page_lock.
 */
static int ext4_writepage(struct page *page,
                          struct writeback_control *wbc)
{
        int ret = 0;
        loff_t size;
        unsigned int len;
        struct buffer_head *page_bufs = NULL;
        struct inode *inode = page->mapping->host;
        struct ext4_io_submit io_submit;
        bool keep_towrite = false;

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
                ext4_invalidatepage(page, 0, PAGE_SIZE);
                unlock_page(page);
                return -EIO;
        }

        trace_ext4_writepage(page);
        size = i_size_read(inode);
        if (page->index == size >> PAGE_SHIFT)
                len = size & ~PAGE_MASK;
        else
                len = PAGE_SIZE;

        page_bufs = page_buffers(page);
        /*
         * We cannot do block allocation or other extent handling in this
         * function. If there are buffers needing that, we have to redirty
         * the page. But we may reach here when we do a journal commit via
         * journal_submit_inode_data_buffers() and in that case we must write
         * allocated buffers to achieve data=ordered mode guarantees.
         *
         * Also, if there is only one buffer per page (the fs block
         * size == the page size), if one buffer needs block
         * allocation or needs to modify the extent tree to clear the
         * unwritten flag, we know that the page can't be written at
         * all, so we might as well refuse the write immediately.
         * Unfortunately if the block size != page size, we can't as
         * easily detect this case using ext4_walk_page_buffers(), but
         * for the extremely common case, this is an optimization that
         * skips a useless round trip through ext4_bio_write_page().
         */
        if (ext4_walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                   ext4_bh_delay_or_unwritten)) {
                redirty_page_for_writepage(wbc, page);
                if ((current->flags & PF_MEMALLOC) ||
                    (inode->i_sb->s_blocksize == PAGE_SIZE)) {
                        /*
                         * For memory cleaning there's no point in writing only
                         * some buffers. So just bail out. Warn if we came here
                         * from direct reclaim.
                         */
                        WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD))
                                                        == PF_MEMALLOC);
                        unlock_page(page);
                        return 0;
                }
                keep_towrite = true;
        }

        if (PageChecked(page) && ext4_should_journal_data(inode))
                /*
                 * It's mmapped pagecache.  Add buffers and journal it.  There
                 * doesn't seem much point in redirtying the page here.
                 */
                return __ext4_journalled_writepage(page, len);

        ext4_io_submit_init(&io_submit, wbc);
        io_submit.io_end = ext4_init_io_end(inode, GFP_NOFS);
        if (!io_submit.io_end) {
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return -ENOMEM;
        }
        ret = ext4_bio_write_page(&io_submit, page, len, wbc, keep_towrite);
        ext4_io_submit(&io_submit);
        /* Drop io_end reference we got from init */
        ext4_put_io_end_defer(io_submit.io_end);
        return ret;
}

static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page)
{
        int len;
        loff_t size;
        int err;

        BUG_ON(page->index != mpd->first_page);
        clear_page_dirty_for_io(page);
        /*
         * We have to be very careful here!  Nothing protects writeback path
         * against i_size changes and the page can be writeably mapped into
         * page tables. So an application can be growing i_size and writing
         * data through mmap while writeback runs. clear_page_dirty_for_io()
         * write-protects our page in page tables and the page cannot get
         * written to again until we release page lock. So only after
         * clear_page_dirty_for_io() we are safe to sample i_size for
         * ext4_bio_write_page() to zero-out tail of the written page. We rely
         * on the barrier provided by TestClearPageDirty in
         * clear_page_dirty_for_io() to make sure i_size is really sampled only
         * after page tables are updated.
         */
        size = i_size_read(mpd->inode);
        if (page->index == size >> PAGE_SHIFT)
                len = size & ~PAGE_MASK;
        else
                len = PAGE_SIZE;
        err = ext4_bio_write_page(&mpd->io_submit, page, len, mpd->wbc, false);
        if (!err)
                mpd->wbc->nr_to_write--;
        mpd->first_page++;

        return err;
}

#define BH_FLAGS ((1 << BH_Unwritten) | (1 << BH_Delay))

/*
 * mballoc gives us at most this number of blocks...
 * XXX: That seems to be only a limitation of ext4_mb_normalize_request().
 * The rest of mballoc seems to handle chunks up to full group size.
 */
#define MAX_WRITEPAGES_EXTENT_LEN 2048

/*
 * mpage_add_bh_to_extent - try to add bh to extent of blocks to map
 *
 * @mpd - extent of blocks
 * @lblk - logical number of the block in the file
 * @bh - buffer head we want to add to the extent
 *
 * The function is used to collect contig. blocks in the same state. If the
 * buffer doesn't require mapping for writeback and we haven't started the
 * extent of buffers to map yet, the function returns 'true' immediately - the
 * caller can write the buffer right away. Otherwise the function returns true
 * if the block has been added to the extent, false if the block couldn't be
 * added.
 */
static bool mpage_add_bh_to_extent(struct mpage_da_data *mpd, ext4_lblk_t lblk,
                                   struct buffer_head *bh)
{
        struct ext4_map_blocks *map = &mpd->map;

        /* Buffer that doesn't need mapping for writeback? */
        if (!buffer_dirty(bh) || !buffer_mapped(bh) ||
            (!buffer_delay(bh) && !buffer_unwritten(bh))) {
                /* So far no extent to map => we write the buffer right away */
                if (map->m_len == 0)
                        return true;
                return false;
        }

        /* First block in the extent? */
        if (map->m_len == 0) {
                /* We cannot map unless handle is started... */
                if (!mpd->do_map)
                        return false;
                map->m_lblk = lblk;
                map->m_len = 1;
                map->m_flags = bh->b_state & BH_FLAGS;
                return true;
        }

        /* Don't go larger than mballoc is willing to allocate */
        if (map->m_len >= MAX_WRITEPAGES_EXTENT_LEN)
                return false;

        /* Can we merge the block to our big extent? */
        if (lblk == map->m_lblk + map->m_len &&
            (bh->b_state & BH_FLAGS) == map->m_flags) {
                map->m_len++;
                return true;
        }
        return false;
}

/*
 * mpage_process_page_bufs - submit page buffers for IO or add them to extent
 *
 * @mpd - extent of blocks for mapping
 * @head - the first buffer in the page
 * @bh - buffer we should start processing from
 * @lblk - logical number of the block in the file corresponding to @bh
 *
 * Walk through page buffers from @bh upto @head (exclusive) and either submit
 * the page for IO if all buffers in this page were mapped and there's no
 * accumulated extent of buffers to map or add buffers in the page to the
 * extent of buffers to map. The function returns 1 if the caller can continue
 * by processing the next page, 0 if it should stop adding buffers to the
 * extent to map because we cannot extend it anymore. It can also return value
 * < 0 in case of error during IO submission.
 */
static int mpage_process_page_bufs(struct mpage_da_data *mpd,
                                   struct buffer_head *head,
                                   struct buffer_head *bh,
                                   ext4_lblk_t lblk)
{
        struct inode *inode = mpd->inode;
        int err;
        ext4_lblk_t blocks = (i_size_read(inode) + i_blocksize(inode) - 1)
                                                        >> inode->i_blkbits;

        do {
                BUG_ON(buffer_locked(bh));

                if (lblk >= blocks || !mpage_add_bh_to_extent(mpd, lblk, bh)) {
                        /* Found extent to map? */
                        if (mpd->map.m_len)
                                return 0;
                        /* Buffer needs mapping and handle is not started? */
                        if (!mpd->do_map)
                                return 0;
                        /* Everything mapped so far and we hit EOF */
                        break;
                }
        } while (lblk++, (bh = bh->b_this_page) != head);
        /* So far everything mapped? Submit the page for IO. */
        if (mpd->map.m_len == 0) {
                err = mpage_submit_page(mpd, head->b_page);
                if (err < 0)
                        return err;
        }
        return lblk < blocks;
}

/*
 * mpage_map_buffers - update buffers corresponding to changed extent and
 *                     submit fully mapped pages for IO
 *
 * @mpd - description of extent to map, on return next extent to map
 *
 * Scan buffers corresponding to changed extent (we expect corresponding pages
 * to be already locked) and update buffer state according to new extent state.
 * We map delalloc buffers to their physical location, clear unwritten bits,
 * and mark buffers as uninit when we perform writes to unwritten extents
 * and do extent conversion after IO is finished. If the last page is not fully
 * mapped, we update @map to the next extent in the last page that needs
 * mapping. Otherwise we submit the page for IO.
 */
static int mpage_map_and_submit_buffers(struct mpage_da_data *mpd)
{
        struct pagevec pvec;
        int nr_pages, i;
        struct inode *inode = mpd->inode;
        struct buffer_head *head, *bh;
        int bpp_bits = PAGE_SHIFT - inode->i_blkbits;
        pgoff_t start, end;
        ext4_lblk_t lblk;
        sector_t pblock;
        int err;

        start = mpd->map.m_lblk >> bpp_bits;
        end = (mpd->map.m_lblk + mpd->map.m_len - 1) >> bpp_bits;
        lblk = start << bpp_bits;
        pblock = mpd->map.m_pblk;

        pagevec_init(&pvec);
        while (start <= end) {
                nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping,
                                                &start, end);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        bh = head = page_buffers(page);
                        do {
                                if (lblk < mpd->map.m_lblk)
                                        continue;
                                if (lblk >= mpd->map.m_lblk + mpd->map.m_len) {
                                        /*
                                         * Buffer after end of mapped extent.
                                         * Find next buffer in the page to map.
                                         */
                                        mpd->map.m_len = 0;
                                        mpd->map.m_flags = 0;
                                        /*
                                         * FIXME: If dioread_nolock supports
                                         * blocksize < pagesize, we need to make
                                         * sure we add size mapped so far to
                                         * io_end->size as the following call
                                         * can submit the page for IO.
                                         */
                                        err = mpage_process_page_bufs(mpd, head,
                                                                      bh, lblk);
                                        pagevec_release(&pvec);
                                        if (err > 0)
                                                err = 0;
                                        return err;
                                }
                                if (buffer_delay(bh)) {
                                        clear_buffer_delay(bh);
                                        bh->b_blocknr = pblock++;
                                }
                                clear_buffer_unwritten(bh);
                        } while (lblk++, (bh = bh->b_this_page) != head);

                        /*
                         * FIXME: This is going to break if dioread_nolock
                         * supports blocksize < pagesize as we will try to
                         * convert potentially unmapped parts of inode.
                         */
                        mpd->io_submit.io_end->size += PAGE_SIZE;
                        /* Page fully mapped - let IO run! */
                        err = mpage_submit_page(mpd, page);
                        if (err < 0) {
                                pagevec_release(&pvec);
                                return err;
                        }
                }
                pagevec_release(&pvec);
        }
        /* Extent fully mapped and matches with page boundary. We are done. */
        mpd->map.m_len = 0;
        mpd->map.m_flags = 0;
        return 0;
}

static int mpage_map_one_extent(handle_t *handle, struct mpage_da_data *mpd)
{
        struct inode *inode = mpd->inode;
        struct ext4_map_blocks *map = &mpd->map;
        int get_blocks_flags;
        int err, dioread_nolock;

        trace_ext4_da_write_pages_extent(inode, map);
        /*
         * Call ext4_map_blocks() to allocate any delayed allocation blocks, or
         * to convert an unwritten extent to be initialized (in the case
         * where we have written into one or more preallocated blocks).  It is
         * possible that we're going to need more metadata blocks than
         * previously reserved. However we must not fail because we're in
         * writeback and there is nothing we can do about it so it might result
         * in data loss.  So use reserved blocks to allocate metadata if
         * possible.
         *
         * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE if
         * the blocks in question are delalloc blocks.  This indicates
         * that the blocks and quotas has already been checked when
         * the data was copied into the page cache.
         */
        get_blocks_flags = EXT4_GET_BLOCKS_CREATE |
                           EXT4_GET_BLOCKS_METADATA_NOFAIL |
                           EXT4_GET_BLOCKS_IO_SUBMIT;
        dioread_nolock = ext4_should_dioread_nolock(inode);
        if (dioread_nolock)
                get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
        if (map->m_flags & (1 << BH_Delay))
                get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;

        err = ext4_map_blocks(handle, inode, map, get_blocks_flags);
        if (err < 0)
                return err;
        if (dioread_nolock && (map->m_flags & EXT4_MAP_UNWRITTEN)) {
                if (!mpd->io_submit.io_end->handle &&
                    ext4_handle_valid(handle)) {
                        mpd->io_submit.io_end->handle = handle->h_rsv_handle;
                        handle->h_rsv_handle = NULL;
                }
                ext4_set_io_unwritten_flag(inode, mpd->io_submit.io_end);
        }

        BUG_ON(map->m_len == 0);
        if (map->m_flags & EXT4_MAP_NEW) {
                clean_bdev_aliases(inode->i_sb->s_bdev, map->m_pblk,
                                   map->m_len);
        }
        return 0;
}

/*
 * mpage_map_and_submit_extent - map extent starting at mpd->lblk of length
 *                               mpd->len and submit pages underlying it for IO
 *
 * @handle - handle for journal operations
 * @mpd - extent to map
 * @give_up_on_write - we set this to true iff there is a fatal error and there
 *                     is no hope of writing the data. The caller should discard
 *                     dirty pages to avoid infinite loops.
 *
 * The function maps extent starting at mpd->lblk of length mpd->len. If it is
 * delayed, blocks are allocated, if it is unwritten, we may need to convert
 * them to initialized or split the described range from larger unwritten
 * extent. Note that we need not map all the described range since allocation
 * can return less blocks or the range is covered by more unwritten extents. We
 * cannot map more because we are limited by reserved transaction credits. On
 * the other hand we always make sure that the last touched page is fully
 * mapped so that it can be written out (and thus forward progress is
 * guaranteed). After mapping we submit all mapped pages for IO.
 */
static int mpage_map_and_submit_extent(handle_t *handle,
                                       struct mpage_da_data *mpd,
                                       bool *give_up_on_write)
{
        struct inode *inode = mpd->inode;
        struct ext4_map_blocks *map = &mpd->map;
        int err;
        loff_t disksize;
        int progress = 0;

        mpd->io_submit.io_end->offset =
                                ((loff_t)map->m_lblk) << inode->i_blkbits;
        do {
                err = mpage_map_one_extent(handle, mpd);
                if (err < 0) {
                        struct super_block *sb = inode->i_sb;

                        if (ext4_forced_shutdown(EXT4_SB(sb)) ||
                            EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
                                goto invalidate_dirty_pages;
                        /*
                         * Let the uper layers retry transient errors.
                         * In the case of ENOSPC, if ext4_count_free_blocks()
                         * is non-zero, a commit should free up blocks.
                         */
                        if ((err == -ENOMEM) ||
                            (err == -ENOSPC && ext4_count_free_clusters(sb))) {
                                if (progress)
                                        goto update_disksize;
                                return err;
                        }
                        ext4_msg(sb, KERN_CRIT,
                                 "Delayed block allocation failed for "
                                 "inode %lu at logical offset %llu with"
                                 " max blocks %u with error %d",
                                 inode->i_ino,
                                 (unsigned long long)map->m_lblk,
                                 (unsigned)map->m_len, -err);
                        ext4_msg(sb, KERN_CRIT,
                                 "This should not happen!! Data will "
                                 "be lost\n");
                        if (err == -ENOSPC)
                                ext4_print_free_blocks(inode);
                invalidate_dirty_pages:
                        *give_up_on_write = true;
                        return err;
                }
                progress = 1;
                /*
                 * Update buffer state, submit mapped pages, and get us new
                 * extent to map
                 */
                err = mpage_map_and_submit_buffers(mpd);
                if (err < 0)
                        goto update_disksize;
        } while (map->m_len);

update_disksize:
        /*
         * Update on-disk size after IO is submitted.  Races with
         * truncate are avoided by checking i_size under i_data_sem.
         */
        disksize = ((loff_t)mpd->first_page) << PAGE_SHIFT;
        if (disksize > EXT4_I(inode)->i_disksize) {
                int err2;
                loff_t i_size;

                down_write(&EXT4_I(inode)->i_data_sem);
                i_size = i_size_read(inode);
                if (disksize > i_size)
                        disksize = i_size;
                if (disksize > EXT4_I(inode)->i_disksize)
                        EXT4_I(inode)->i_disksize = disksize;
                up_write(&EXT4_I(inode)->i_data_sem);
                err2 = ext4_mark_inode_dirty(handle, inode);
                if (err2)
                        ext4_error(inode->i_sb,
                                   "Failed to mark inode %lu dirty",
                                   inode->i_ino);
                if (!err)
                        err = err2;
        }
        return err;
}

/*
 * Calculate the total number of credits to reserve for one writepages
 * iteration. This is called from ext4_writepages(). We map an extent of
 * up to MAX_WRITEPAGES_EXTENT_LEN blocks and then we go on and finish mapping
 * the last partial page. So in total we can map MAX_WRITEPAGES_EXTENT_LEN +
 * bpp - 1 blocks in bpp different extents.
 */
static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
        int bpp = ext4_journal_blocks_per_page(inode);

        return ext4_meta_trans_blocks(inode,
                                MAX_WRITEPAGES_EXTENT_LEN + bpp - 1, bpp);
}

/*
 * mpage_prepare_extent_to_map - find & lock contiguous range of dirty pages
 *                               and underlying extent to map
 *
 * @mpd - where to look for pages
 *
 * Walk dirty pages in the mapping. If they are fully mapped, submit them for
 * IO immediately. When we find a page which isn't mapped we start accumulating
 * extent of buffers underlying these pages that needs mapping (formed by
 * either delayed or unwritten buffers). We also lock the pages containing
 * these buffers. The extent found is returned in @mpd structure (starting at
 * mpd->lblk with length mpd->len blocks).
 *
 * Note that this function can attach bios to one io_end structure which are
 * neither logically nor physically contiguous. Although it may seem as an
 * unnecessary complication, it is actually inevitable in blocksize < pagesize
 * case as we need to track IO to all buffers underlying a page in one io_end.
 */
static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
{
        struct address_space *mapping = mpd->inode->i_mapping;
        struct pagevec pvec;
        unsigned int nr_pages;
        long left = mpd->wbc->nr_to_write;
        pgoff_t index = mpd->first_page;
        pgoff_t end = mpd->last_page;
        int tag;
        int i, err = 0;
        int blkbits = mpd->inode->i_blkbits;
        ext4_lblk_t lblk;
        struct buffer_head *head;

        if (mpd->wbc->sync_mode == WB_SYNC_ALL || mpd->wbc->tagged_writepages)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;

        pagevec_init(&pvec);
        mpd->map.m_len = 0;
        mpd->next_page = index;
        while (index <= end) {
                nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
                                tag);
                if (nr_pages == 0)
                        goto out;

                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        /*
                         * Accumulated enough dirty pages? This doesn't apply
                         * to WB_SYNC_ALL mode. For integrity sync we have to
                         * keep going because someone may be concurrently
                         * dirtying pages, and we might have synced a lot of
                         * newly appeared dirty pages, but have not synced all
                         * of the old dirty pages.
                         */
                        if (mpd->wbc->sync_mode == WB_SYNC_NONE && left <= 0)
                                goto out;

                        /* If we can't merge this page, we are done. */
                        if (mpd->map.m_len > 0 && mpd->next_page != page->index)
                                goto out;

                        lock_page(page);
                        /*
                         * If the page is no longer dirty, or its mapping no
                         * longer corresponds to inode we are writing (which
                         * means it has been truncated or invalidated), or the
                         * page is already under writeback and we are not doing
                         * a data integrity writeback, skip the page
                         */
                        if (!PageDirty(page) ||
                            (PageWriteback(page) &&
                             (mpd->wbc->sync_mode == WB_SYNC_NONE)) ||
                            unlikely(page->mapping != mapping)) {
                                unlock_page(page);
                                continue;
                        }

                        wait_on_page_writeback(page);
                        BUG_ON(PageWriteback(page));

                        if (mpd->map.m_len == 0)
                                mpd->first_page = page->index;
                        mpd->next_page = page->index + 1;
                        /* Add all dirty buffers to mpd */
                        lblk = ((ext4_lblk_t)page->index) <<
                                (PAGE_SHIFT - blkbits);
                        head = page_buffers(page);
                        err = mpage_process_page_bufs(mpd, head, head, lblk);
                        if (err <= 0)
                                goto out;
                        err = 0;
                        left--;
                }
                pagevec_release(&pvec);
                cond_resched();
        }
        return 0;
out:
        pagevec_release(&pvec);
        return err;
}

static int ext4_writepages(struct address_space *mapping,
                           struct writeback_control *wbc)
{
        pgoff_t writeback_index = 0;
        long nr_to_write = wbc->nr_to_write;
        int range_whole = 0;
        int cycled = 1;
        handle_t *handle = NULL;
        struct mpage_da_data mpd;
        struct inode *inode = mapping->host;
        int needed_blocks, rsv_blocks = 0, ret = 0;
        struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
        bool done;
        struct blk_plug plug;
        bool give_up_on_write = false;

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

        percpu_down_read(&sbi->s_journal_flag_rwsem);
        trace_ext4_writepages(inode, wbc);

        /*
         * No pages to write? This is mainly a kludge to avoid starting
         * a transaction for special inodes like journal inode on last iput()
         * because that could violate lock ordering on umount
         */
        if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                goto out_writepages;

        if (ext4_should_journal_data(inode)) {
                ret = generic_writepages(mapping, wbc);
                goto out_writepages;
        }

        /*
         * If the filesystem has aborted, it is read-only, so return
         * right away instead of dumping stack traces later on that
         * will obscure the real source of the problem.  We test
         * EXT4_MF_FS_ABORTED instead of sb->s_flag's SB_RDONLY because
         * the latter could be true if the filesystem is mounted
         * read-only, and in that case, ext4_writepages should
         * *never* be called, so if that ever happens, we would want
         * the stack trace.
         */
        if (unlikely(ext4_forced_shutdown(EXT4_SB(mapping->host->i_sb)) ||
                     sbi->s_mount_flags & EXT4_MF_FS_ABORTED)) {
                ret = -EROFS;
                goto out_writepages;
        }

        if (ext4_should_dioread_nolock(inode)) {
                /*
                 * We may need to convert up to one extent per block in
                 * the page and we may dirty the inode.
                 */
                rsv_blocks = 1 + (PAGE_SIZE >> inode->i_blkbits);
        }

        /*
         * If we have inline data and arrive here, it means that
         * we will soon create the block for the 1st page, so
         * we'd better clear the inline data here.
         */
        if (ext4_has_inline_data(inode)) {
                /* Just inode will be modified... */
                handle = ext4_journal_start(inode, EXT4_HT_INODE, 1);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out_writepages;
                }
                BUG_ON(ext4_test_inode_state(inode,
                                EXT4_STATE_MAY_INLINE_DATA));
                ext4_destroy_inline_data(handle, inode);
                ext4_journal_stop(handle);
        }

        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                range_whole = 1;

        if (wbc->range_cyclic) {
                writeback_index = mapping->writeback_index;
                if (writeback_index)
                        cycled = 0;
                mpd.first_page = writeback_index;
                mpd.last_page = -1;
        } else {
                mpd.first_page = wbc->range_start >> PAGE_SHIFT;
                mpd.last_page = wbc->range_end >> PAGE_SHIFT;
        }

        mpd.inode = inode;
        mpd.wbc = wbc;
        ext4_io_submit_init(&mpd.io_submit, wbc);
retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, mpd.first_page, mpd.last_page);
        done = false;
        blk_start_plug(&plug);

        /*
         * First writeback pages that don't need mapping - we can avoid
         * starting a transaction unnecessarily and also avoid being blocked
         * in the block layer on device congestion while having transaction
         * started.
         */
        mpd.do_map = 0;
        mpd.io_submit.io_end = ext4_init_io_end(inode, GFP_KERNEL);
        if (!mpd.io_submit.io_end) {
                ret = -ENOMEM;
                goto unplug;
        }
        ret = mpage_prepare_extent_to_map(&mpd);
        /* Submit prepared bio */
        ext4_io_submit(&mpd.io_submit);
        ext4_put_io_end_defer(mpd.io_submit.io_end);
        mpd.io_submit.io_end = NULL;
        /* Unlock pages we didn't use */
        mpage_release_unused_pages(&mpd, false);
        if (ret < 0)
                goto unplug;

        while (!done && mpd.first_page <= mpd.last_page) {
                /* For each extent of pages we use new io_end */
                mpd.io_submit.io_end = ext4_init_io_end(inode, GFP_KERNEL);
                if (!mpd.io_submit.io_end) {
                        ret = -ENOMEM;
                        break;
                }

                /*
                 * We have two constraints: We find one extent to map and we
                 * must always write out whole page (makes a difference when
                 * blocksize < pagesize) so that we don't block on IO when we
                 * try to write out the rest of the page. Journalled mode is
                 * not supported by delalloc.
                 */
                BUG_ON(ext4_should_journal_data(inode));
                needed_blocks = ext4_da_writepages_trans_blocks(inode);

                /* start a new transaction */
                handle = ext4_journal_start_with_reserve(inode,
                                EXT4_HT_WRITE_PAGE, needed_blocks, rsv_blocks);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        ext4_msg(inode->i_sb, KERN_CRIT, "%s: jbd2_start: "
                               "%ld pages, ino %lu; err %d", __func__,
                                wbc->nr_to_write, inode->i_ino, ret);
                        /* Release allocated io_end */
                        ext4_put_io_end(mpd.io_submit.io_end);
                        mpd.io_submit.io_end = NULL;
                        break;
                }
                mpd.do_map = 1;

                trace_ext4_da_write_pages(inode, mpd.first_page, mpd.wbc);
                ret = mpage_prepare_extent_to_map(&mpd);
                if (!ret) {
                        if (mpd.map.m_len)
                                ret = mpage_map_and_submit_extent(handle, &mpd,
                                        &give_up_on_write);
                        else {
                                /*
                                 * We scanned the whole range (or exhausted
                                 * nr_to_write), submitted what was mapped and
                                 * didn't find anything needing mapping. We are
                                 * done.
                                 */
                                done = true;
                        }
                }
                /*
                 * Caution: If the handle is synchronous,
                 * ext4_journal_stop() can wait for transaction commit
                 * to finish which may depend on writeback of pages to
                 * complete or on page lock to be released.  In that
                 * case, we have to wait until after after we have
                 * submitted all the IO, released page locks we hold,
                 * and dropped io_end reference (for extent conversion
                 * to be able to complete) before stopping the handle.
                 */
                if (!ext4_handle_valid(handle) || handle->h_sync == 0) {
                        ext4_journal_stop(handle);
                        handle = NULL;
                        mpd.do_map = 0;
                }
                /* Submit prepared bio */
                ext4_io_submit(&mpd.io_submit);
                /* Unlock pages we didn't use */
                mpage_release_unused_pages(&mpd, give_up_on_write);
                /*
                 * Drop our io_end reference we got from init. We have
                 * to be careful and use deferred io_end finishing if
                 * we are still holding the transaction as we can
                 * release the last reference to io_end which may end
                 * up doing unwritten extent conversion.
                 */
                if (handle) {
                        ext4_put_io_end_defer(mpd.io_submit.io_end);
                        ext4_journal_stop(handle);
                } else
                        ext4_put_io_end(mpd.io_submit.io_end);
                mpd.io_submit.io_end = NULL;

                if (ret == -ENOSPC && sbi->s_journal) {
                        /*
                         * Commit the transaction which would
                         * free blocks released in the transaction
                         * and try again
                         */
                        jbd2_journal_force_commit_nested(sbi->s_journal);
                        ret = 0;
                        continue;
                }
                /* Fatal error - ENOMEM, EIO... */
                if (ret)
                        break;
        }
unplug:
        blk_finish_plug(&plug);
        if (!ret && !cycled && wbc->nr_to_write > 0) {
                cycled = 1;
                mpd.last_page = writeback_index - 1;
                mpd.first_page = 0;
                goto retry;
        }

        /* Update index */
        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                /*
                 * Set the writeback_index so that range_cyclic
                 * mode will write it back later
                 */
                mapping->writeback_index = mpd.first_page;

out_writepages:
        trace_ext4_writepages_result(inode, wbc, ret,
                                     nr_to_write - wbc->nr_to_write);
        percpu_up_read(&sbi->s_journal_flag_rwsem);
        return ret;
}

static int ext4_dax_writepages(struct address_space *mapping,
                               struct writeback_control *wbc)
{
        int ret;
        long nr_to_write = wbc->nr_to_write;
        struct inode *inode = mapping->host;
        struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);

        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;

        percpu_down_read(&sbi->s_journal_flag_rwsem);
        trace_ext4_writepages(inode, wbc);

        ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev, wbc);
        trace_ext4_writepages_result(inode, wbc, ret,
                                     nr_to_write - wbc->nr_to_write);
        percpu_up_read(&sbi->s_journal_flag_rwsem);
        return ret;
}

static int ext4_nonda_switch(struct super_block *sb)
{
        s64 free_clusters, dirty_clusters;
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        /*
         * switch to non delalloc mode if we are running low
         * on free block. The free block accounting via percpu
         * counters can get slightly wrong with percpu_counter_batch getting
         * accumulated on each CPU without updating global counters
         * Delalloc need an accurate free block accounting. So switch
         * to non delalloc when we are near to error range.
         */
        free_clusters =
                percpu_counter_read_positive(&sbi->s_freeclusters_counter);
        dirty_clusters =
                percpu_counter_read_positive(&sbi->s_dirtyclusters_counter);
        /*
         * Start pushing delalloc when 1/2 of free blocks are dirty.
         */
        if (dirty_clusters && (free_clusters < 2 * dirty_clusters))
                try_to_writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);

        if (2 * free_clusters < 3 * dirty_clusters ||
            free_clusters < (dirty_clusters + EXT4_FREECLUSTERS_WATERMARK)) {
                /*
                 * free block count is less than 150% of dirty blocks
                 * or free blocks is less than watermark
                 */
                return 1;
        }
        return 0;
}

/* We always reserve for an inode update; the superblock could be there too */
static int ext4_da_write_credits(struct inode *inode, loff_t pos, unsigned len)
{
        if (likely(ext4_has_feature_large_file(inode->i_sb)))
                return 1;

        if (pos + len <= 0x7fffffffULL)