Btrfs: balance btree more often

[linux-2.6] / fs / gfs2 / bmap.c

/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
 * Copyright (C) 2004-2006 Red Hat, Inc.  All rights reserved.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License version 2.
 */

#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/buffer_head.h>
#include <linux/gfs2_ondisk.h>
#include <linux/crc32.h>

#include "gfs2.h"
#include "incore.h"
#include "bmap.h"
#include "glock.h"
#include "inode.h"
#include "meta_io.h"
#include "quota.h"
#include "rgrp.h"
#include "trans.h"
#include "dir.h"
#include "util.h"
#include "ops_address.h"

/* This doesn't need to be that large as max 64 bit pointers in a 4k
 * block is 512, so __u16 is fine for that. It saves stack space to
 * keep it small.
 */
struct metapath {
        struct buffer_head *mp_bh[GFS2_MAX_META_HEIGHT];
        __u16 mp_list[GFS2_MAX_META_HEIGHT];
};

typedef int (*block_call_t) (struct gfs2_inode *ip, struct buffer_head *dibh,
                             struct buffer_head *bh, __be64 *top,
                             __be64 *bottom, unsigned int height,
                             void *data);

struct strip_mine {
        int sm_first;
        unsigned int sm_height;
};

/**
 * gfs2_unstuffer_page - unstuff a stuffed inode into a block cached by a page
 * @ip: the inode
 * @dibh: the dinode buffer
 * @block: the block number that was allocated
 * @private: any locked page held by the caller process
 *
 * Returns: errno
 */

static int gfs2_unstuffer_page(struct gfs2_inode *ip, struct buffer_head *dibh,
                               u64 block, struct page *page)
{
        struct inode *inode = &ip->i_inode;
        struct buffer_head *bh;
        int release = 0;

        if (!page || page->index) {
                page = grab_cache_page(inode->i_mapping, 0);
                if (!page)
                        return -ENOMEM;
                release = 1;
        }

        if (!PageUptodate(page)) {
                void *kaddr = kmap(page);

                memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode),
                       ip->i_disksize);
                memset(kaddr + ip->i_disksize, 0,
                       PAGE_CACHE_SIZE - ip->i_disksize);
                kunmap(page);

                SetPageUptodate(page);
        }

        if (!page_has_buffers(page))
                create_empty_buffers(page, 1 << inode->i_blkbits,
                                     (1 << BH_Uptodate));

        bh = page_buffers(page);

        if (!buffer_mapped(bh))
                map_bh(bh, inode->i_sb, block);

        set_buffer_uptodate(bh);
        if (!gfs2_is_jdata(ip))
                mark_buffer_dirty(bh);
        if (!gfs2_is_writeback(ip))
                gfs2_trans_add_bh(ip->i_gl, bh, 0);

        if (release) {
                unlock_page(page);
                page_cache_release(page);
        }

        return 0;
}

/**
 * gfs2_unstuff_dinode - Unstuff a dinode when the data has grown too big
 * @ip: The GFS2 inode to unstuff
 * @unstuffer: the routine that handles unstuffing a non-zero length file
 * @private: private data for the unstuffer
 *
 * This routine unstuffs a dinode and returns it to a "normal" state such
 * that the height can be grown in the traditional way.
 *
 * Returns: errno
 */

int gfs2_unstuff_dinode(struct gfs2_inode *ip, struct page *page)
{
        struct buffer_head *bh, *dibh;
        struct gfs2_dinode *di;
        u64 block = 0;
        int isdir = gfs2_is_dir(ip);
        int error;

        down_write(&ip->i_rw_mutex);

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                goto out;

        if (ip->i_disksize) {
                /* Get a free block, fill it with the stuffed data,
                   and write it out to disk */

                unsigned int n = 1;
                block = gfs2_alloc_block(ip, &n);
                if (isdir) {
                        gfs2_trans_add_unrevoke(GFS2_SB(&ip->i_inode), block, 1);
                        error = gfs2_dir_get_new_buffer(ip, block, &bh);
                        if (error)
                                goto out_brelse;
                        gfs2_buffer_copy_tail(bh, sizeof(struct gfs2_meta_header),
                                              dibh, sizeof(struct gfs2_dinode));
                        brelse(bh);
                } else {
                        error = gfs2_unstuffer_page(ip, dibh, block, page);
                        if (error)
                                goto out_brelse;
                }
        }

        /*  Set up the pointer to the new block  */

        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
        di = (struct gfs2_dinode *)dibh->b_data;
        gfs2_buffer_clear_tail(dibh, sizeof(struct gfs2_dinode));

        if (ip->i_disksize) {
                *(__be64 *)(di + 1) = cpu_to_be64(block);
                gfs2_add_inode_blocks(&ip->i_inode, 1);
                di->di_blocks = cpu_to_be64(gfs2_get_inode_blocks(&ip->i_inode));
        }

        ip->i_height = 1;
        di->di_height = cpu_to_be16(1);

out_brelse:
        brelse(dibh);
out:
        up_write(&ip->i_rw_mutex);
        return error;
}


/**
 * find_metapath - Find path through the metadata tree
 * @sdp: The superblock
 * @mp: The metapath to return the result in
 * @block: The disk block to look up
 * @height: The pre-calculated height of the metadata tree
 *
 *   This routine returns a struct metapath structure that defines a path
 *   through the metadata of inode "ip" to get to block "block".
 *
 *   Example:
 *   Given:  "ip" is a height 3 file, "offset" is 101342453, and this is a
 *   filesystem with a blocksize of 4096.
 *
 *   find_metapath() would return a struct metapath structure set to:
 *   mp_offset = 101342453, mp_height = 3, mp_list[0] = 0, mp_list[1] = 48,
 *   and mp_list[2] = 165.
 *
 *   That means that in order to get to the block containing the byte at
 *   offset 101342453, we would load the indirect block pointed to by pointer
 *   0 in the dinode.  We would then load the indirect block pointed to by
 *   pointer 48 in that indirect block.  We would then load the data block
 *   pointed to by pointer 165 in that indirect block.
 *
 *             ----------------------------------------
 *             | Dinode |                             |
 *             |        |                            4|
 *             |        |0 1 2 3 4 5                 9|
 *             |        |                            6|
 *             ----------------------------------------
 *                       |
 *                       |
 *                       V
 *             ----------------------------------------
 *             | Indirect Block                       |
 *             |                                     5|
 *             |            4 4 4 4 4 5 5            1|
 *             |0           5 6 7 8 9 0 1            2|
 *             ----------------------------------------
 *                                |
 *                                |
 *                                V
 *             ----------------------------------------
 *             | Indirect Block                       |
 *             |                         1 1 1 1 1   5|
 *             |                         6 6 6 6 6   1|
 *             |0                        3 4 5 6 7   2|
 *             ----------------------------------------
 *                                           |
 *                                           |
 *                                           V
 *             ----------------------------------------
 *             | Data block containing offset         |
 *             |            101342453                 |
 *             |                                      |
 *             |                                      |
 *             ----------------------------------------
 *
 */

static void find_metapath(const struct gfs2_sbd *sdp, u64 block,
                          struct metapath *mp, unsigned int height)
{
        unsigned int i;

        for (i = height; i--;)
                mp->mp_list[i] = do_div(block, sdp->sd_inptrs);

}

static inline unsigned int metapath_branch_start(const struct metapath *mp)
{
        if (mp->mp_list[0] == 0)
                return 2;
        return 1;
}

/**
 * metapointer - Return pointer to start of metadata in a buffer
 * @height: The metadata height (0 = dinode)
 * @mp: The metapath
 *
 * Return a pointer to the block number of the next height of the metadata
 * tree given a buffer containing the pointer to the current height of the
 * metadata tree.
 */

static inline __be64 *metapointer(unsigned int height, const struct metapath *mp)
{
        struct buffer_head *bh = mp->mp_bh[height];
        unsigned int head_size = (height > 0) ?
                sizeof(struct gfs2_meta_header) : sizeof(struct gfs2_dinode);
        return ((__be64 *)(bh->b_data + head_size)) + mp->mp_list[height];
}

/**
 * lookup_metapath - Walk the metadata tree to a specific point
 * @ip: The inode
 * @mp: The metapath
 *
 * Assumes that the inode's buffer has already been looked up and
 * hooked onto mp->mp_bh[0] and that the metapath has been initialised
 * by find_metapath().
 *
 * If this function encounters part of the tree which has not been
 * allocated, it returns the current height of the tree at the point
 * at which it found the unallocated block. Blocks which are found are
 * added to the mp->mp_bh[] list.
 *
 * Returns: error or height of metadata tree
 */

static int lookup_metapath(struct gfs2_inode *ip, struct metapath *mp)
{
        unsigned int end_of_metadata = ip->i_height - 1;
        unsigned int x;
        __be64 *ptr;
        u64 dblock;
        int ret;

        for (x = 0; x < end_of_metadata; x++) {
                ptr = metapointer(x, mp);
                dblock = be64_to_cpu(*ptr);
                if (!dblock)
                        return x + 1;

                ret = gfs2_meta_indirect_buffer(ip, x+1, dblock, 0, &mp->mp_bh[x+1]);
                if (ret)
                        return ret;
        }

        return ip->i_height;
}

static inline void release_metapath(struct metapath *mp)
{
        int i;

        for (i = 0; i < GFS2_MAX_META_HEIGHT; i++) {
                if (mp->mp_bh[i] == NULL)
                        break;
                brelse(mp->mp_bh[i]);
        }
}

/**
 * gfs2_extent_length - Returns length of an extent of blocks
 * @start: Start of the buffer
 * @len: Length of the buffer in bytes
 * @ptr: Current position in the buffer
 * @limit: Max extent length to return (0 = unlimited)
 * @eob: Set to 1 if we hit "end of block"
 *
 * If the first block is zero (unallocated) it will return the number of
 * unallocated blocks in the extent, otherwise it will return the number
 * of contiguous blocks in the extent.
 *
 * Returns: The length of the extent (minimum of one block)
 */

static inline unsigned int gfs2_extent_length(void *start, unsigned int len, __be64 *ptr, unsigned limit, int *eob)
{
        const __be64 *end = (start + len);
        const __be64 *first = ptr;
        u64 d = be64_to_cpu(*ptr);

        *eob = 0;
        do {
                ptr++;
                if (ptr >= end)
                        break;
                if (limit && --limit == 0)
                        break;
                if (d)
                        d++;
        } while(be64_to_cpu(*ptr) == d);
        if (ptr >= end)
                *eob = 1;
        return (ptr - first);
}

static inline void bmap_lock(struct gfs2_inode *ip, int create)
{
        if (create)
                down_write(&ip->i_rw_mutex);
        else
                down_read(&ip->i_rw_mutex);
}

static inline void bmap_unlock(struct gfs2_inode *ip, int create)
{
        if (create)
                up_write(&ip->i_rw_mutex);
        else
                up_read(&ip->i_rw_mutex);
}

static inline __be64 *gfs2_indirect_init(struct metapath *mp,
                                         struct gfs2_glock *gl, unsigned int i,
                                         unsigned offset, u64 bn)
{
        __be64 *ptr = (__be64 *)(mp->mp_bh[i - 1]->b_data +
                       ((i > 1) ? sizeof(struct gfs2_meta_header) :
                                 sizeof(struct gfs2_dinode)));
        BUG_ON(i < 1);
        BUG_ON(mp->mp_bh[i] != NULL);
        mp->mp_bh[i] = gfs2_meta_new(gl, bn);
        gfs2_trans_add_bh(gl, mp->mp_bh[i], 1);
        gfs2_metatype_set(mp->mp_bh[i], GFS2_METATYPE_IN, GFS2_FORMAT_IN);
        gfs2_buffer_clear_tail(mp->mp_bh[i], sizeof(struct gfs2_meta_header));
        ptr += offset;
        *ptr = cpu_to_be64(bn);
        return ptr;
}

enum alloc_state {
        ALLOC_DATA = 0,
        ALLOC_GROW_DEPTH = 1,
        ALLOC_GROW_HEIGHT = 2,
        /* ALLOC_UNSTUFF = 3,   TBD and rather complicated */
};

/**
 * gfs2_bmap_alloc - Build a metadata tree of the requested height
 * @inode: The GFS2 inode
 * @lblock: The logical starting block of the extent
 * @bh_map: This is used to return the mapping details
 * @mp: The metapath
 * @sheight: The starting height (i.e. whats already mapped)
 * @height: The height to build to
 * @maxlen: The max number of data blocks to alloc
 *
 * In this routine we may have to alloc:
 *   i) Indirect blocks to grow the metadata tree height
 *  ii) Indirect blocks to fill in lower part of the metadata tree
 * iii) Data blocks
 *
 * The function is in two parts. The first part works out the total
 * number of blocks which we need. The second part does the actual
 * allocation asking for an extent at a time (if enough contiguous free
 * blocks are available, there will only be one request per bmap call)
 * and uses the state machine to initialise the blocks in order.
 *
 * Returns: errno on error
 */

static int gfs2_bmap_alloc(struct inode *inode, const sector_t lblock,
                           struct buffer_head *bh_map, struct metapath *mp,
                           const unsigned int sheight,
                           const unsigned int height,
                           const unsigned int maxlen)
{
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        struct buffer_head *dibh = mp->mp_bh[0];
        u64 bn, dblock = 0;
        unsigned n, i, blks, alloced = 0, iblks = 0, branch_start = 0;
        unsigned dblks = 0;
        unsigned ptrs_per_blk;
        const unsigned end_of_metadata = height - 1;
        int eob = 0;
        enum alloc_state state;
        __be64 *ptr;
        __be64 zero_bn = 0;

        BUG_ON(sheight < 1);
        BUG_ON(dibh == NULL);

        gfs2_trans_add_bh(ip->i_gl, dibh, 1);

        if (height == sheight) {
                struct buffer_head *bh;
                /* Bottom indirect block exists, find unalloced extent size */
                ptr = metapointer(end_of_metadata, mp);
                bh = mp->mp_bh[end_of_metadata];
                dblks = gfs2_extent_length(bh->b_data, bh->b_size, ptr, maxlen,
                                           &eob);
                BUG_ON(dblks < 1);
                state = ALLOC_DATA;
        } else {
                /* Need to allocate indirect blocks */
                ptrs_per_blk = height > 1 ? sdp->sd_inptrs : sdp->sd_diptrs;
                dblks = min(maxlen, ptrs_per_blk - mp->mp_list[end_of_metadata]);
                if (height == ip->i_height) {
                        /* Writing into existing tree, extend tree down */
                        iblks = height - sheight;
                        state = ALLOC_GROW_DEPTH;
                } else {
                        /* Building up tree height */
                        state = ALLOC_GROW_HEIGHT;
                        iblks = height - ip->i_height;
                        branch_start = metapath_branch_start(mp);
                        iblks += (height - branch_start);
                }
        }

        /* start of the second part of the function (state machine) */

        blks = dblks + iblks;
        i = sheight;
        do {
                n = blks - alloced;
                bn = gfs2_alloc_block(ip, &n);
                alloced += n;
                if (state != ALLOC_DATA || gfs2_is_jdata(ip))
                        gfs2_trans_add_unrevoke(sdp, bn, n);
                switch (state) {
                /* Growing height of tree */
                case ALLOC_GROW_HEIGHT:
                        if (i == 1) {
                                ptr = (__be64 *)(dibh->b_data +
                                                 sizeof(struct gfs2_dinode));
                                zero_bn = *ptr;
                        }
                        for (; i - 1 < height - ip->i_height && n > 0; i++, n--)
                                gfs2_indirect_init(mp, ip->i_gl, i, 0, bn++);
                        if (i - 1 == height - ip->i_height) {
                                i--;
                                gfs2_buffer_copy_tail(mp->mp_bh[i],
                                                sizeof(struct gfs2_meta_header),
                                                dibh, sizeof(struct gfs2_dinode));
                                gfs2_buffer_clear_tail(dibh,
                                                sizeof(struct gfs2_dinode) +
                                                sizeof(__be64));
                                ptr = (__be64 *)(mp->mp_bh[i]->b_data +
                                        sizeof(struct gfs2_meta_header));
                                *ptr = zero_bn;
                                state = ALLOC_GROW_DEPTH;
                                for(i = branch_start; i < height; i++) {
                                        if (mp->mp_bh[i] == NULL)
                                                break;
                                        brelse(mp->mp_bh[i]);
                                        mp->mp_bh[i] = NULL;
                                }
                                i = branch_start;
                        }
                        if (n == 0)
                                break;
                /* Branching from existing tree */
                case ALLOC_GROW_DEPTH:
                        if (i > 1 && i < height)
                                gfs2_trans_add_bh(ip->i_gl, mp->mp_bh[i-1], 1);
                        for (; i < height && n > 0; i++, n--)
                                gfs2_indirect_init(mp, ip->i_gl, i,
                                                   mp->mp_list[i-1], bn++);
                        if (i == height)
                                state = ALLOC_DATA;
                        if (n == 0)
                                break;
                /* Tree complete, adding data blocks */
                case ALLOC_DATA:
                        BUG_ON(n > dblks);
                        BUG_ON(mp->mp_bh[end_of_metadata] == NULL);
                        gfs2_trans_add_bh(ip->i_gl, mp->mp_bh[end_of_metadata], 1);
                        dblks = n;
                        ptr = metapointer(end_of_metadata, mp);
                        dblock = bn;
                        while (n-- > 0)
                                *ptr++ = cpu_to_be64(bn++);
                        break;
                }
        } while (state != ALLOC_DATA);

        ip->i_height = height;
        gfs2_add_inode_blocks(&ip->i_inode, alloced);
        gfs2_dinode_out(ip, mp->mp_bh[0]->b_data);
        map_bh(bh_map, inode->i_sb, dblock);
        bh_map->b_size = dblks << inode->i_blkbits;
        set_buffer_new(bh_map);
        return 0;
}

/**
 * gfs2_block_map - Map a block from an inode to a disk block
 * @inode: The inode
 * @lblock: The logical block number
 * @bh_map: The bh to be mapped
 * @create: True if its ok to alloc blocks to satify the request
 *
 * Sets buffer_mapped() if successful, sets buffer_boundary() if a
 * read of metadata will be required before the next block can be
 * mapped. Sets buffer_new() if new blocks were allocated.
 *
 * Returns: errno
 */

int gfs2_block_map(struct inode *inode, sector_t lblock,
                   struct buffer_head *bh_map, int create)
{
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        unsigned int bsize = sdp->sd_sb.sb_bsize;
        const unsigned int maxlen = bh_map->b_size >> inode->i_blkbits;
        const u64 *arr = sdp->sd_heightsize;
        __be64 *ptr;
        u64 size;
        struct metapath mp;
        int ret;
        int eob;
        unsigned int len;
        struct buffer_head *bh;
        u8 height;

        BUG_ON(maxlen == 0);

        memset(mp.mp_bh, 0, sizeof(mp.mp_bh));
        bmap_lock(ip, create);
        clear_buffer_mapped(bh_map);
        clear_buffer_new(bh_map);
        clear_buffer_boundary(bh_map);
        if (gfs2_is_dir(ip)) {
                bsize = sdp->sd_jbsize;
                arr = sdp->sd_jheightsize;
        }

        ret = gfs2_meta_inode_buffer(ip, &mp.mp_bh[0]);
        if (ret)
                goto out;

        height = ip->i_height;
        size = (lblock + 1) * bsize;
        while (size > arr[height])
                height++;
        find_metapath(sdp, lblock, &mp, height);
        ret = 1;
        if (height > ip->i_height || gfs2_is_stuffed(ip))
                goto do_alloc;
        ret = lookup_metapath(ip, &mp);
        if (ret < 0)
                goto out;
        if (ret != ip->i_height)
                goto do_alloc;
        ptr = metapointer(ip->i_height - 1, &mp);
        if (*ptr == 0)
                goto do_alloc;
        map_bh(bh_map, inode->i_sb, be64_to_cpu(*ptr));
        bh = mp.mp_bh[ip->i_height - 1];
        len = gfs2_extent_length(bh->b_data, bh->b_size, ptr, maxlen, &eob);
        bh_map->b_size = (len << inode->i_blkbits);
        if (eob)
                set_buffer_boundary(bh_map);
        ret = 0;
out:
        release_metapath(&mp);
        bmap_unlock(ip, create);
        return ret;

do_alloc:
        /* All allocations are done here, firstly check create flag */
        if (!create) {
                BUG_ON(gfs2_is_stuffed(ip));
                ret = 0;
                goto out;
        }

        /* At this point ret is the tree depth of already allocated blocks */
        ret = gfs2_bmap_alloc(inode, lblock, bh_map, &mp, ret, height, maxlen);
        goto out;
}

/*
 * Deprecated: do not use in new code
 */
int gfs2_extent_map(struct inode *inode, u64 lblock, int *new, u64 *dblock, unsigned *extlen)
{
        struct buffer_head bh = { .b_state = 0, .b_blocknr = 0 };
        int ret;
        int create = *new;

        BUG_ON(!extlen);
        BUG_ON(!dblock);
        BUG_ON(!new);

        bh.b_size = 1 << (inode->i_blkbits + (create ? 0 : 5));
        ret = gfs2_block_map(inode, lblock, &bh, create);
        *extlen = bh.b_size >> inode->i_blkbits;
        *dblock = bh.b_blocknr;
        if (buffer_new(&bh))
                *new = 1;
        else
                *new = 0;
        return ret;
}

/**
 * recursive_scan - recursively scan through the end of a file
 * @ip: the inode
 * @dibh: the dinode buffer
 * @mp: the path through the metadata to the point to start
 * @height: the height the recursion is at
 * @block: the indirect block to look at
 * @first: 1 if this is the first block
 * @bc: the call to make for each piece of metadata
 * @data: data opaque to this function to pass to @bc
 *
 * When this is first called @height and @block should be zero and
 * @first should be 1.
 *
 * Returns: errno
 */

static int recursive_scan(struct gfs2_inode *ip, struct buffer_head *dibh,
                          struct metapath *mp, unsigned int height,
                          u64 block, int first, block_call_t bc,
                          void *data)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct buffer_head *bh = NULL;
        __be64 *top, *bottom;
        u64 bn;
        int error;
        int mh_size = sizeof(struct gfs2_meta_header);

        if (!height) {
                error = gfs2_meta_inode_buffer(ip, &bh);
                if (error)
                        return error;
                dibh = bh;

                top = (__be64 *)(bh->b_data + sizeof(struct gfs2_dinode)) + mp->mp_list[0];
                bottom = (__be64 *)(bh->b_data + sizeof(struct gfs2_dinode)) + sdp->sd_diptrs;
        } else {
                error = gfs2_meta_indirect_buffer(ip, height, block, 0, &bh);
                if (error)
                        return error;

                top = (__be64 *)(bh->b_data + mh_size) +
                                  (first ? mp->mp_list[height] : 0);

                bottom = (__be64 *)(bh->b_data + mh_size) + sdp->sd_inptrs;
        }

        error = bc(ip, dibh, bh, top, bottom, height, data);
        if (error)
                goto out;

        if (height < ip->i_height - 1)
                for (; top < bottom; top++, first = 0) {
                        if (!*top)
                                continue;

                        bn = be64_to_cpu(*top);

                        error = recursive_scan(ip, dibh, mp, height + 1, bn,
                                               first, bc, data);
                        if (error)
                                break;
                }

out:
        brelse(bh);
        return error;
}

/**
 * do_strip - Look for a layer a particular layer of the file and strip it off
 * @ip: the inode
 * @dibh: the dinode buffer
 * @bh: A buffer of pointers
 * @top: The first pointer in the buffer
 * @bottom: One more than the last pointer
 * @height: the height this buffer is at
 * @data: a pointer to a struct strip_mine
 *
 * Returns: errno
 */

static int do_strip(struct gfs2_inode *ip, struct buffer_head *dibh,
                    struct buffer_head *bh, __be64 *top, __be64 *bottom,
                    unsigned int height, void *data)
{
        struct strip_mine *sm = data;
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct gfs2_rgrp_list rlist;
        u64 bn, bstart;
        u32 blen;
        __be64 *p;
        unsigned int rg_blocks = 0;
        int metadata;
        unsigned int revokes = 0;
        int x;
        int error;

        if (!*top)
                sm->sm_first = 0;

        if (height != sm->sm_height)
                return 0;

        if (sm->sm_first) {
                top++;
                sm->sm_first = 0;
        }

        metadata = (height != ip->i_height - 1);
        if (metadata)
                revokes = (height) ? sdp->sd_inptrs : sdp->sd_diptrs;

        error = gfs2_rindex_hold(sdp, &ip->i_alloc->al_ri_gh);
        if (error)
                return error;

        memset(&rlist, 0, sizeof(struct gfs2_rgrp_list));
        bstart = 0;
        blen = 0;

        for (p = top; p < bottom; p++) {
                if (!*p)
                        continue;

                bn = be64_to_cpu(*p);

                if (bstart + blen == bn)
                        blen++;
                else {
                        if (bstart)
                                gfs2_rlist_add(sdp, &rlist, bstart);

                        bstart = bn;
                        blen = 1;
                }
        }

        if (bstart)
                gfs2_rlist_add(sdp, &rlist, bstart);
        else
                goto out; /* Nothing to do */

        gfs2_rlist_alloc(&rlist, LM_ST_EXCLUSIVE);

        for (x = 0; x < rlist.rl_rgrps; x++) {
                struct gfs2_rgrpd *rgd;
                rgd = rlist.rl_ghs[x].gh_gl->gl_object;
                rg_blocks += rgd->rd_length;
        }

        error = gfs2_glock_nq_m(rlist.rl_rgrps, rlist.rl_ghs);
        if (error)
                goto out_rlist;

        error = gfs2_trans_begin(sdp, rg_blocks + RES_DINODE +
                                 RES_INDIRECT + RES_STATFS + RES_QUOTA,
                                 revokes);
        if (error)
                goto out_rg_gunlock;

        down_write(&ip->i_rw_mutex);

        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
        gfs2_trans_add_bh(ip->i_gl, bh, 1);

        bstart = 0;
        blen = 0;

        for (p = top; p < bottom; p++) {
                if (!*p)
                        continue;

                bn = be64_to_cpu(*p);

                if (bstart + blen == bn)
                        blen++;
                else {
                        if (bstart) {
                                if (metadata)
                                        gfs2_free_meta(ip, bstart, blen);
                                else
                                        gfs2_free_data(ip, bstart, blen);
                        }

                        bstart = bn;
                        blen = 1;
                }

                *p = 0;
                gfs2_add_inode_blocks(&ip->i_inode, -1);
        }
        if (bstart) {
                if (metadata)
                        gfs2_free_meta(ip, bstart, blen);
                else
                        gfs2_free_data(ip, bstart, blen);
        }

        ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;

        gfs2_dinode_out(ip, dibh->b_data);

        up_write(&ip->i_rw_mutex);

        gfs2_trans_end(sdp);

out_rg_gunlock:
        gfs2_glock_dq_m(rlist.rl_rgrps, rlist.rl_ghs);
out_rlist:
        gfs2_rlist_free(&rlist);
out:
        gfs2_glock_dq_uninit(&ip->i_alloc->al_ri_gh);
        return error;
}

/**
 * do_grow - Make a file look bigger than it is
 * @ip: the inode
 * @size: the size to set the file to
 *
 * Called with an exclusive lock on @ip.
 *
 * Returns: errno
 */

static int do_grow(struct gfs2_inode *ip, u64 size)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct gfs2_alloc *al;
        struct buffer_head *dibh;
        int error;

        al = gfs2_alloc_get(ip);
        if (!al)
                return -ENOMEM;

        error = gfs2_quota_lock_check(ip);
        if (error)
                goto out;

        al->al_requested = sdp->sd_max_height + RES_DATA;

        error = gfs2_inplace_reserve(ip);
        if (error)
                goto out_gunlock_q;

        error = gfs2_trans_begin(sdp,
                        sdp->sd_max_height + al->al_rgd->rd_length +
                        RES_JDATA + RES_DINODE + RES_STATFS + RES_QUOTA, 0);
        if (error)
                goto out_ipres;

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                goto out_end_trans;

        if (size > sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode)) {
                if (gfs2_is_stuffed(ip)) {
                        error = gfs2_unstuff_dinode(ip, NULL);
                        if (error)
                                goto out_brelse;
                }
        }

        ip->i_disksize = size;
        ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
        gfs2_dinode_out(ip, dibh->b_data);

out_brelse:
        brelse(dibh);
out_end_trans:
        gfs2_trans_end(sdp);
out_ipres:
        gfs2_inplace_release(ip);
out_gunlock_q:
        gfs2_quota_unlock(ip);
out:
        gfs2_alloc_put(ip);
        return error;
}


/**
 * gfs2_block_truncate_page - Deal with zeroing out data for truncate
 *
 * This is partly borrowed from ext3.
 */
static int gfs2_block_truncate_page(struct address_space *mapping)
{
        struct inode *inode = mapping->host;
        struct gfs2_inode *ip = GFS2_I(inode);
        loff_t from = inode->i_size;
        unsigned long index = from >> PAGE_CACHE_SHIFT;
        unsigned offset = from & (PAGE_CACHE_SIZE-1);
        unsigned blocksize, iblock, length, pos;
        struct buffer_head *bh;
        struct page *page;
        int err;

        page = grab_cache_page(mapping, index);
        if (!page)
                return 0;

        blocksize = inode->i_sb->s_blocksize;
        length = blocksize - (offset & (blocksize - 1));
        iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);

        /* Find the buffer that contains "offset" */
        bh = page_buffers(page);
        pos = blocksize;
        while (offset >= pos) {
                bh = bh->b_this_page;
                iblock++;
                pos += blocksize;
        }

        err = 0;

        if (!buffer_mapped(bh)) {
                gfs2_block_map(inode, iblock, bh, 0);
                /* unmapped? It's a hole - nothing to do */
                if (!buffer_mapped(bh))
                        goto unlock;
        }

        /* Ok, it's mapped. Make sure it's up-to-date */
        if (PageUptodate(page))
                set_buffer_uptodate(bh);

        if (!buffer_uptodate(bh)) {
                err = -EIO;
                ll_rw_block(READ, 1, &bh);
                wait_on_buffer(bh);
                /* Uhhuh. Read error. Complain and punt. */
                if (!buffer_uptodate(bh))
                        goto unlock;
                err = 0;
        }

        if (!gfs2_is_writeback(ip))
                gfs2_trans_add_bh(ip->i_gl, bh, 0);

        zero_user(page, offset, length);

unlock:
        unlock_page(page);
        page_cache_release(page);
        return err;
}

static int trunc_start(struct gfs2_inode *ip, u64 size)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct buffer_head *dibh;
        int journaled = gfs2_is_jdata(ip);
        int error;

        error = gfs2_trans_begin(sdp,
                                 RES_DINODE + (journaled ? RES_JDATA : 0), 0);
        if (error)
                return error;

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                goto out;

        if (gfs2_is_stuffed(ip)) {
                ip->i_disksize = size;
                ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
                gfs2_trans_add_bh(ip->i_gl, dibh, 1);
                gfs2_dinode_out(ip, dibh->b_data);
                gfs2_buffer_clear_tail(dibh, sizeof(struct gfs2_dinode) + size);
                error = 1;

        } else {
                if (size & (u64)(sdp->sd_sb.sb_bsize - 1))
                        error = gfs2_block_truncate_page(ip->i_inode.i_mapping);

                if (!error) {
                        ip->i_disksize = size;
                        ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
                        ip->i_diskflags |= GFS2_DIF_TRUNC_IN_PROG;
                        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
                        gfs2_dinode_out(ip, dibh->b_data);
                }
        }

        brelse(dibh);

out:
        gfs2_trans_end(sdp);
        return error;
}

static int trunc_dealloc(struct gfs2_inode *ip, u64 size)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        unsigned int height = ip->i_height;
        u64 lblock;
        struct metapath mp;
        int error;

        if (!size)
                lblock = 0;
        else
                lblock = (size - 1) >> sdp->sd_sb.sb_bsize_shift;

        find_metapath(sdp, lblock, &mp, ip->i_height);
        if (!gfs2_alloc_get(ip))
                return -ENOMEM;

        error = gfs2_quota_hold(ip, NO_QUOTA_CHANGE, NO_QUOTA_CHANGE);
        if (error)
                goto out;

        while (height--) {
                struct strip_mine sm;
                sm.sm_first = !!size;
                sm.sm_height = height;

                error = recursive_scan(ip, NULL, &mp, 0, 0, 1, do_strip, &sm);
                if (error)
                        break;
        }

        gfs2_quota_unhold(ip);

out:
        gfs2_alloc_put(ip);
        return error;
}

static int trunc_end(struct gfs2_inode *ip)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct buffer_head *dibh;
        int error;

        error = gfs2_trans_begin(sdp, RES_DINODE, 0);
        if (error)
                return error;

        down_write(&ip->i_rw_mutex);

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                goto out;

        if (!ip->i_disksize) {
                ip->i_height = 0;
                ip->i_goal = ip->i_no_addr;
                gfs2_buffer_clear_tail(dibh, sizeof(struct gfs2_dinode));
        }
        ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
        ip->i_diskflags &= ~GFS2_DIF_TRUNC_IN_PROG;

        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
        gfs2_dinode_out(ip, dibh->b_data);
        brelse(dibh);

out:
        up_write(&ip->i_rw_mutex);
        gfs2_trans_end(sdp);
        return error;
}

/**
 * do_shrink - make a file smaller
 * @ip: the inode
 * @size: the size to make the file
 * @truncator: function to truncate the last partial block
 *
 * Called with an exclusive lock on @ip.
 *
 * Returns: errno
 */

static int do_shrink(struct gfs2_inode *ip, u64 size)
{
        int error;

        error = trunc_start(ip, size);
        if (error < 0)
                return error;
        if (error > 0)
                return 0;

        error = trunc_dealloc(ip, size);
        if (!error)
                error = trunc_end(ip);

        return error;
}

static int do_touch(struct gfs2_inode *ip, u64 size)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct buffer_head *dibh;
        int error;

        error = gfs2_trans_begin(sdp, RES_DINODE, 0);
        if (error)
                return error;

        down_write(&ip->i_rw_mutex);

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                goto do_touch_out;

        ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
        gfs2_trans_add_bh(ip->i_gl, dibh, 1);
        gfs2_dinode_out(ip, dibh->b_data);
        brelse(dibh);

do_touch_out:
        up_write(&ip->i_rw_mutex);
        gfs2_trans_end(sdp);
        return error;
}

/**
 * gfs2_truncatei - make a file a given size
 * @ip: the inode
 * @size: the size to make the file
 * @truncator: function to truncate the last partial block
 *
 * The file size can grow, shrink, or stay the same size.
 *
 * Returns: errno
 */

int gfs2_truncatei(struct gfs2_inode *ip, u64 size)
{
        int error;

        if (gfs2_assert_warn(GFS2_SB(&ip->i_inode), S_ISREG(ip->i_inode.i_mode)))
                return -EINVAL;

        if (size > ip->i_disksize)
                error = do_grow(ip, size);
        else if (size < ip->i_disksize)
                error = do_shrink(ip, size);
        else
                /* update time stamps */
                error = do_touch(ip, size);

        return error;
}

int gfs2_truncatei_resume(struct gfs2_inode *ip)
{
        int error;
        error = trunc_dealloc(ip, ip->i_disksize);
        if (!error)
                error = trunc_end(ip);
        return error;
}

int gfs2_file_dealloc(struct gfs2_inode *ip)
{
        return trunc_dealloc(ip, 0);
}

/**
 * gfs2_write_alloc_required - figure out if a write will require an allocation
 * @ip: the file being written to
 * @offset: the offset to write to
 * @len: the number of bytes being written
 * @alloc_required: set to 1 if an alloc is required, 0 otherwise
 *
 * Returns: errno
 */

int gfs2_write_alloc_required(struct gfs2_inode *ip, u64 offset,
                              unsigned int len, int *alloc_required)
{
        struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
        struct buffer_head bh;
        unsigned int shift;
        u64 lblock, lblock_stop, size;
        u64 end_of_file;

        *alloc_required = 0;

        if (!len)
                return 0;

        if (gfs2_is_stuffed(ip)) {
                if (offset + len >
                    sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode))
                        *alloc_required = 1;
                return 0;
        }

        *alloc_required = 1;
        shift = sdp->sd_sb.sb_bsize_shift;
        BUG_ON(gfs2_is_dir(ip));
        end_of_file = (ip->i_disksize + sdp->sd_sb.sb_bsize - 1) >> shift;
        lblock = offset >> shift;
        lblock_stop = (offset + len + sdp->sd_sb.sb_bsize - 1) >> shift;
        if (lblock_stop > end_of_file)
                return 0;

        size = (lblock_stop - lblock) << shift;
        do {
                bh.b_state = 0;
                bh.b_size = size;
                gfs2_block_map(&ip->i_inode, lblock, &bh, 0);
                if (!buffer_mapped(&bh))
                        return 0;
                size -= bh.b_size;
                lblock += (bh.b_size >> ip->i_inode.i_blkbits);
        } while(size > 0);

        *alloc_required = 0;
        return 0;
}