bmap.c

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/*
 * 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/spinlock.h>
#include <linux/completion.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.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 "super.h"
#include "trans.h"
#include "dir.h"
#include "util.h"
#include "trace_gfs2.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];
};

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

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 = find_or_create_page(inode->i_mapping, 0, GFP_NOFS);
        if (!page)
            return -ENOMEM;
        release = 1;
    }

    if (!PageUptodate(page)) {
        void *kaddr = kmap(page);
        u64 dsize = i_size_read(inode);
 
        if (dsize > (dibh->b_size - sizeof(struct gfs2_dinode)))
            dsize = dibh->b_size - sizeof(struct gfs2_dinode);

        memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode), dsize);
        memset(kaddr + dsize, 0, PAGE_CACHE_SIZE - dsize);
        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;
}

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

        unsigned int n = 1;
        error = gfs2_alloc_blocks(ip, &block, &n, 0, NULL);
        if (error)
            goto out_brelse;
        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 (i_size_read(&ip->i_inode)) {
        *(__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;
}


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;
}

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];
}

static void gfs2_metapath_ra(struct gfs2_glock *gl,
                 const struct buffer_head *bh, const __be64 *pos)
{
    struct buffer_head *rabh;
    const __be64 *endp = (const __be64 *)(bh->b_data + bh->b_size);
    const __be64 *t;

    for (t = pos; t < endp; t++) {
        if (!*t)
            continue;

        rabh = gfs2_getbuf(gl, be64_to_cpu(*t), CREATE);
        if (trylock_buffer(rabh)) {
            if (!buffer_uptodate(rabh)) {
                rabh->b_end_io = end_buffer_read_sync;
                submit_bh(READA | REQ_META, rabh);
                continue;
            }
            unlock_buffer(rabh);
        }
        brelse(rabh);
    }
}

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, &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]);
    }
}

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 */
};

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 super_block *sb = sdp->sd_vfs;
    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 ret;
    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 {
        int error;
        n = blks - alloced;
        error = gfs2_alloc_blocks(ip, &bn, &n, 0, NULL);
        if (error)
            return error;
        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++);
            if (buffer_zeronew(bh_map)) {
                ret = sb_issue_zeroout(sb, dblock, dblks,
                               GFP_NOFS);
                if (ret) {
                    fs_err(sdp,
                           "Failed to zero data buffers\n");
                    clear_buffer_zeronew(bh_map);
                }
            }
            break;
        }
    } while ((state != ALLOC_DATA) || !dblock);

    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;
}

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);
    trace_gfs2_bmap(ip, bh_map, lblock, create, 1);
    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);
    trace_gfs2_bmap(ip, bh_map, lblock, create, ret);
    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;
}

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

    error = gfs2_rindex_update(sdp);
    if (error)
        return 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;
    else if (ip->i_depth)
        revokes = sdp->sd_inptrs;

    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(ip, &rlist, bstart);

            bstart = bn;
            blen = 1;
        }
    }

    if (bstart)
        gfs2_rlist_add(ip, &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;

    if (gfs2_rs_active(ip->i_res)) /* needs to be done with the rgrp glock held */
        gfs2_rs_deltree(ip, ip->i_res);

    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;
    btotal = 0;

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

        bn = be64_to_cpu(*p);

        if (bstart + blen == bn)
            blen++;
        else {
            if (bstart) {
                __gfs2_free_blocks(ip, bstart, blen, metadata);
                btotal += blen;
            }

            bstart = bn;
            blen = 1;
        }

        *p = 0;
        gfs2_add_inode_blocks(&ip->i_inode, -1);
    }
    if (bstart) {
        __gfs2_free_blocks(ip, bstart, blen, metadata);
        btotal += blen;
    }

    gfs2_statfs_change(sdp, 0, +btotal, 0);
    gfs2_quota_change(ip, -(s64)btotal, ip->i_inode.i_uid,
              ip->i_inode.i_gid);

    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:
    return error;
}

static int recursive_scan(struct gfs2_inode *ip, struct buffer_head *dibh,
              struct metapath *mp, unsigned int height,
              u64 block, int first, struct strip_mine *sm)
{
    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, &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 = do_strip(ip, dibh, bh, top, bottom, height, sm);
    if (error)
        goto out;

    if (height < ip->i_height - 1) {

        gfs2_metapath_ra(ip->i_gl, bh, top);

        for (; top < bottom; top++, first = 0) {
            if (!*top)
                continue;

            bn = be64_to_cpu(*top);

            error = recursive_scan(ip, dibh, mp, height + 1, bn,
                           first, sm);
            if (error)
                break;
        }
    }
out:
    brelse(bh);
    return error;
}


static int gfs2_block_truncate_page(struct address_space *mapping, loff_t from)
{
    struct inode *inode = mapping->host;
    struct gfs2_inode *ip = GFS2_I(inode);
    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 = find_or_create_page(mapping, index, GFP_NOFS);
    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);
    mark_buffer_dirty(bh);
unlock:
    unlock_page(page);
    page_cache_release(page);
    return err;
}

static int trunc_start(struct inode *inode, u64 oldsize, u64 newsize)
{
    struct gfs2_inode *ip = GFS2_I(inode);
    struct gfs2_sbd *sdp = GFS2_SB(inode);
    struct address_space *mapping = inode->i_mapping;
    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;

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

    if (gfs2_is_stuffed(ip)) {
        gfs2_buffer_clear_tail(dibh, sizeof(struct gfs2_dinode) + newsize);
    } else {
        if (newsize & (u64)(sdp->sd_sb.sb_bsize - 1)) {
            error = gfs2_block_truncate_page(mapping, newsize);
            if (error)
                goto out_brelse;
        }
        ip->i_diskflags |= GFS2_DIF_TRUNC_IN_PROG;
    }

    i_size_write(inode, newsize);
    ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
    gfs2_dinode_out(ip, dibh->b_data);

    truncate_pagecache(inode, oldsize, newsize);
out_brelse:
    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);
    error = gfs2_rindex_update(sdp);
    if (error)
        return error;

    error = gfs2_quota_hold(ip, NO_QUOTA_CHANGE, NO_QUOTA_CHANGE);
    if (error)
        return error;

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

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

    gfs2_quota_unhold(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 (!i_size_read(&ip->i_inode)) {
        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;
}

static int do_shrink(struct inode *inode, u64 oldsize, u64 newsize)
{
    struct gfs2_inode *ip = GFS2_I(inode);
    int error;

    error = trunc_start(inode, oldsize, newsize);
    if (error < 0)
        return error;
    if (gfs2_is_stuffed(ip))
        return 0;

    error = trunc_dealloc(ip, newsize);
    if (error == 0)
        error = trunc_end(ip);

    return error;
}

void gfs2_trim_blocks(struct inode *inode)
{
    u64 size = inode->i_size;
    int ret;

    ret = do_shrink(inode, size, size);
    WARN_ON(ret != 0);
}

static int do_grow(struct inode *inode, u64 size)
{
    struct gfs2_inode *ip = GFS2_I(inode);
    struct gfs2_sbd *sdp = GFS2_SB(inode);
    struct buffer_head *dibh;
    int error;
    int unstuff = 0;

    if (gfs2_is_stuffed(ip) &&
        (size > (sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode)))) {
        error = gfs2_quota_lock_check(ip);
        if (error)
            return error;

        error = gfs2_inplace_reserve(ip, 1);
        if (error)
            goto do_grow_qunlock;
        unstuff = 1;
    }

    error = gfs2_trans_begin(sdp, RES_DINODE + RES_STATFS + RES_RG_BIT, 0);
    if (error)
        goto do_grow_release;

    if (unstuff) {
        error = gfs2_unstuff_dinode(ip, NULL);
        if (error)
            goto do_end_trans;
    }

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

    i_size_write(inode, 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);
    brelse(dibh);

do_end_trans:
    gfs2_trans_end(sdp);
do_grow_release:
    if (unstuff) {
        gfs2_inplace_release(ip);
do_grow_qunlock:
        gfs2_quota_unlock(ip);
    }
    return error;
}

int gfs2_setattr_size(struct inode *inode, u64 newsize)
{
    int ret;
    u64 oldsize;

    BUG_ON(!S_ISREG(inode->i_mode));

    ret = inode_newsize_ok(inode, newsize);
    if (ret)
        return ret;

    inode_dio_wait(inode);

    oldsize = inode->i_size;
    if (newsize >= oldsize)
        return do_grow(inode, newsize);

    return do_shrink(inode, oldsize, newsize);
}

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

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

int gfs2_write_alloc_required(struct gfs2_inode *ip, u64 offset,
                  unsigned int len)
{
    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;

    if (!len)
        return 0;

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

    shift = sdp->sd_sb.sb_bsize_shift;
    BUG_ON(gfs2_is_dir(ip));
    end_of_file = (i_size_read(&ip->i_inode) + 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 1;

    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 1;
        size -= bh.b_size;
        lblock += (bh.b_size >> ip->i_inode.i_blkbits);
    } while(size > 0);

    return 0;
}