/*
 * gcinode.c - dummy inodes to buffer blocks for garbage collection
 *
 * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Written by Seiji Kihara <kihara@osrg.net>, Amagai Yoshiji <amagai@osrg.net>,
 *            and Ryusuke Konishi <ryusuke@osrg.net>.
 * Revised by Ryusuke Konishi <ryusuke@osrg.net>.
 *
 */
/*
 * This file adds the cache of on-disk blocks to be moved in garbage
 * collection.  The disk blocks are held with dummy inodes (called
 * gcinodes), and this file provides lookup function of the dummy
 * inodes and their buffer read function.
 *
 * Since NILFS2 keeps up multiple checkpoints/snapshots accross GC, it
 * has to treat blocks that belong to a same file but have different
 * checkpoint numbers.  To avoid interference among generations, dummy
 * inodes are managed separatly from actual inodes, and their lookup
 * function (nilfs_gc_iget) is designed to be specified with a
 * checkpoint number argument as well as an inode number.
 *
 * Buffers and pages held by the dummy inodes will be released each
 * time after they are copied to a new log.  Dirty blocks made on the
 * current generation and the blocks to be moved by GC never overlap
 * because the dirty blocks make a new generation; they rather must be
 * written individually.
 */

#include <linux/buffer_head.h>
#include <linux/mpage.h>
#include <linux/hash.h>
#include <linux/swap.h>
#include "nilfs.h"
#include "page.h"
#include "mdt.h"
#include "dat.h"
#include "ifile.h"

static const struct address_space_operations def_gcinode_aops = {
        .sync_page              = block_sync_page,
};

/*
 * nilfs_gccache_submit_read_data() - add data buffer and submit read request
 * @inode - gc inode
 * @blkoff - dummy offset treated as the key for the page cache
 * @pbn - physical block number of the block
 * @vbn - virtual block number of the block, 0 for non-virtual block
 * @out_bh - indirect pointer to a buffer_head struct to receive the results
 *
 * Description: nilfs_gccache_submit_read_data() registers the data buffer
 * specified by @pbn to the GC pagecache with the key @blkoff.
 * This function sets @vbn (@pbn if @vbn is zero) in b_blocknr of the buffer.
 *
 * Return Value: On success, 0 is returned. On Error, one of the following
 * negative error code is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-ENOENT - The block specified with @pbn does not exist.
 */
int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
                                   sector_t pbn, __u64 vbn,
                                   struct buffer_head **out_bh)
{
        struct buffer_head *bh;
        int err;

        bh = nilfs_grab_buffer(inode, inode->i_mapping, blkoff, 0);
        if (unlikely(!bh))
                return -ENOMEM;

        if (buffer_uptodate(bh))
                goto out;

        if (pbn == 0) {
                struct inode *dat_inode = NILFS_I_NILFS(inode)->ns_dat;
                                          /* use original dat, not gc dat. */
                err = nilfs_dat_translate(dat_inode, vbn, &pbn);
                if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
                        brelse(bh);
                        goto failed;
                }
        }

        lock_buffer(bh);
        if (buffer_uptodate(bh)) {
                unlock_buffer(bh);
                goto out;
        }

        if (!buffer_mapped(bh)) {
                bh->b_bdev = NILFS_I_NILFS(inode)->ns_bdev;
                set_buffer_mapped(bh);
        }
        bh->b_blocknr = pbn;
        bh->b_end_io = end_buffer_read_sync;
        get_bh(bh);
        submit_bh(READ, bh);
        if (vbn)
                bh->b_blocknr = vbn;
 out:
        err = 0;
        *out_bh = bh;

 failed:
        unlock_page(bh->b_page);
        page_cache_release(bh->b_page);
        return err;
}

/*
 * nilfs_gccache_submit_read_node() - add node buffer and submit read request
 * @inode - gc inode
 * @pbn - physical block number for the block
 * @vbn - virtual block number for the block
 * @out_bh - indirect pointer to a buffer_head struct to receive the results
 *
 * Description: nilfs_gccache_submit_read_node() registers the node buffer
 * specified by @vbn to the GC pagecache.  @pbn can be supplied by the
 * caller to avoid translation of the disk block address.
 *
 * Return Value: On success, 0 is returned. On Error, one of the following
 * negative error code is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 */
int nilfs_gccache_submit_read_node(struct inode *inode, sector_t pbn,
                                   __u64 vbn, struct buffer_head **out_bh)
{
        int ret = nilfs_btnode_submit_block(&NILFS_I(inode)->i_btnode_cache,
                                            vbn ? : pbn, pbn, out_bh, 0);
        if (ret == -EEXIST) /* internal code (cache hit) */
                ret = 0;
        return ret;
}

int nilfs_gccache_wait_and_mark_dirty(struct buffer_head *bh)
{
        wait_on_buffer(bh);
        if (!buffer_uptodate(bh))
                return -EIO;
        if (buffer_dirty(bh))
                return -EEXIST;

        if (buffer_nilfs_node(bh))
                nilfs_btnode_mark_dirty(bh);
        else
                nilfs_mdt_mark_buffer_dirty(bh);
        return 0;
}

/*
 * nilfs_init_gccache() - allocate and initialize gc_inode hash table
 * @nilfs - the_nilfs
 *
 * Return Value: On success, 0.
 * On error, a negative error code is returned.
 */
int nilfs_init_gccache(struct the_nilfs *nilfs)
{
        int loop;

        BUG_ON(nilfs->ns_gc_inodes_h);

        INIT_LIST_HEAD(&nilfs->ns_gc_inodes);

        nilfs->ns_gc_inodes_h =
                kmalloc(sizeof(struct hlist_head) * NILFS_GCINODE_HASH_SIZE,
                        GFP_NOFS);
        if (nilfs->ns_gc_inodes_h == NULL)
                return -ENOMEM;

        for (loop = 0; loop < NILFS_GCINODE_HASH_SIZE; loop++)
                INIT_HLIST_HEAD(&nilfs->ns_gc_inodes_h[loop]);
        return 0;
}

/*
 * nilfs_destroy_gccache() - free gc_inode hash table
 * @nilfs - the nilfs
 */
void nilfs_destroy_gccache(struct the_nilfs *nilfs)
{
        if (nilfs->ns_gc_inodes_h) {
                nilfs_remove_all_gcinode(nilfs);
                kfree(nilfs->ns_gc_inodes_h);
                nilfs->ns_gc_inodes_h = NULL;
        }
}

static struct inode *alloc_gcinode(struct the_nilfs *nilfs, ino_t ino,
                                   __u64 cno)
{
        struct inode *inode = nilfs_mdt_new_common(nilfs, NULL, ino, GFP_NOFS);
        struct nilfs_inode_info *ii;

        if (!inode)
                return NULL;

        inode->i_op = NULL;
        inode->i_fop = NULL;
        inode->i_mapping->a_ops = &def_gcinode_aops;

        ii = NILFS_I(inode);
        ii->i_cno = cno;
        ii->i_flags = 0;
        ii->i_state = 1 << NILFS_I_GCINODE;
        ii->i_bh = NULL;
        nilfs_bmap_init_gc(ii->i_bmap);

        return inode;
}

static unsigned long ihash(ino_t ino, __u64 cno)
{
        return hash_long((unsigned long)((ino << 2) + cno),
                         NILFS_GCINODE_HASH_BITS);
}

/*
 * nilfs_gc_iget() - find or create gc inode with specified (ino,cno)
 */
struct inode *nilfs_gc_iget(struct the_nilfs *nilfs, ino_t ino, __u64 cno)
{
        struct hlist_head *head = nilfs->ns_gc_inodes_h + ihash(ino, cno);
        struct hlist_node *node;
        struct inode *inode;

        hlist_for_each_entry(inode, node, head, i_hash) {
                if (inode->i_ino == ino && NILFS_I(inode)->i_cno == cno)
                        return inode;
        }

        inode = alloc_gcinode(nilfs, ino, cno);
        if (likely(inode)) {
                hlist_add_head(&inode->i_hash, head);
                list_add(&NILFS_I(inode)->i_dirty, &nilfs->ns_gc_inodes);
        }
        return inode;
}

/*
 * nilfs_clear_gcinode() - clear and free a gc inode
 */
void nilfs_clear_gcinode(struct inode *inode)
{
        nilfs_mdt_clear(inode);
        nilfs_mdt_destroy(inode);
}

/*
 * nilfs_remove_all_gcinode() - remove all inodes from the_nilfs
 */
void nilfs_remove_all_gcinode(struct the_nilfs *nilfs)
{
        struct hlist_head *head = nilfs->ns_gc_inodes_h;
        struct hlist_node *node, *n;
        struct inode *inode;
        int loop;

        for (loop = 0; loop < NILFS_GCINODE_HASH_SIZE; loop++, head++) {
                hlist_for_each_entry_safe(inode, node, n, head, i_hash) {
                        hlist_del_init(&inode->i_hash);
                        list_del_init(&NILFS_I(inode)->i_dirty);
                        nilfs_clear_gcinode(inode); /* might sleep */
                }
        }
}