patch-2_6_7-vs1_9_1_12

[linux-2.6.git] / fs / ext2 / inode.c

/*
 *  linux/fs/ext2/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
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *      (sct@dcs.ed.ac.uk), 1993, 1998
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext2_get_block() by Al Viro, 2000
 */

#include <linux/smp_lock.h>
#include <linux/time.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/module.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>
#include <linux/mpage.h>
#include <linux/vserver/xid.h>
#include "ext2.h"
#include "acl.h"

MODULE_AUTHOR("Remy Card and others");
MODULE_DESCRIPTION("Second Extended Filesystem");
MODULE_LICENSE("GPL");

static int ext2_update_inode(struct inode * inode, int do_sync);

/*
 * Test whether an inode is a fast symlink.
 */
static inline int ext2_inode_is_fast_symlink(struct inode *inode)
{
        int ea_blocks = EXT2_I(inode)->i_file_acl ?
                (inode->i_sb->s_blocksize >> 9) : 0;

        return (S_ISLNK(inode->i_mode) &&
                inode->i_blocks - ea_blocks == 0);
}

/*
 * Called at each iput().
 *
 * The inode may be "bad" if ext2_read_inode() saw an error from
 * ext2_get_inode(), so we need to check that to avoid freeing random disk
 * blocks.
 */
void ext2_put_inode(struct inode *inode)
{
        if (!is_bad_inode(inode))
                ext2_discard_prealloc(inode);
}

static void ext2_truncate_nocheck (struct inode * inode);

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext2_delete_inode (struct inode * inode)
{
        if (is_bad_inode(inode))
                goto no_delete;
        EXT2_I(inode)->i_dtime  = get_seconds();
        mark_inode_dirty(inode);
        ext2_update_inode(inode, inode_needs_sync(inode));

        inode->i_size = 0;
        if (inode->i_blocks)
                ext2_truncate_nocheck(inode);
        ext2_free_inode (inode);

        return;
no_delete:
        clear_inode(inode);     /* We must guarantee clearing of inode... */
}

void ext2_discard_prealloc (struct inode * inode)
{
#ifdef EXT2_PREALLOCATE
        struct ext2_inode_info *ei = EXT2_I(inode);
        write_lock(&ei->i_meta_lock);
        if (ei->i_prealloc_count) {
                unsigned short total = ei->i_prealloc_count;
                unsigned long block = ei->i_prealloc_block;
                ei->i_prealloc_count = 0;
                ei->i_prealloc_block = 0;
                write_unlock(&ei->i_meta_lock);
                ext2_free_blocks (inode, block, total);
                return;
        } else
                write_unlock(&ei->i_meta_lock);
#endif
}

static int ext2_alloc_block (struct inode * inode, unsigned long goal, int *err)
{
#ifdef EXT2FS_DEBUG
        static unsigned long alloc_hits, alloc_attempts;
#endif
        unsigned long result;


#ifdef EXT2_PREALLOCATE
        struct ext2_inode_info *ei = EXT2_I(inode);
        write_lock(&ei->i_meta_lock);
        if (ei->i_prealloc_count &&
            (goal == ei->i_prealloc_block || goal + 1 == ei->i_prealloc_block))
        {
                result = ei->i_prealloc_block++;
                ei->i_prealloc_count--;
                write_unlock(&ei->i_meta_lock);
                ext2_debug ("preallocation hit (%lu/%lu).\n",
                            ++alloc_hits, ++alloc_attempts);
        } else {
                write_unlock(&ei->i_meta_lock);
                ext2_discard_prealloc (inode);
                ext2_debug ("preallocation miss (%lu/%lu).\n",
                            alloc_hits, ++alloc_attempts);
                if (S_ISREG(inode->i_mode))
                        result = ext2_new_block (inode, goal, 
                                 &ei->i_prealloc_count,
                                 &ei->i_prealloc_block, err);
                else
                        result = ext2_new_block (inode, goal, 0, 0, err);
        }
#else
        result = ext2_new_block (inode, goal, 0, 0, err);
#endif
        return result;
}

typedef struct {
        u32     *p;
        u32     key;
        struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, u32 *v)
{
        p->key = *(p->p = v);
        p->bh = bh;
}

static inline int verify_chain(Indirect *from, Indirect *to)
{
        while (from <= to && from->key == *from->p)
                from++;
        return (from > to);
}

/**
 *      ext2_block_to_path - parse the block number into array of offsets
 *      @inode: inode in question (we are only interested in its superblock)
 *      @i_block: block number to be parsed
 *      @offsets: array to store the offsets in
 *      @boundary: set this non-zero if the referred-to block is likely to be
 *             followed (on disk) by an indirect block.
 *      To store the locations of file's data ext2 uses a data structure common
 *      for UNIX filesystems - tree of pointers anchored in the inode, with
 *      data blocks at leaves and indirect blocks in intermediate nodes.
 *      This function translates the block number into path in that tree -
 *      return value is the path length and @offsets[n] is the offset of
 *      pointer to (n+1)th node in the nth one. If @block is out of range
 *      (negative or too large) warning is printed and zero returned.
 *
 *      Note: function doesn't find node addresses, so no IO is needed. All
 *      we need to know is the capacity of indirect blocks (taken from the
 *      inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext2_block_to_path(struct inode *inode,
                        long i_block, int offsets[4], int *boundary)
{
        int ptrs = EXT2_ADDR_PER_BLOCK(inode->i_sb);
        int ptrs_bits = EXT2_ADDR_PER_BLOCK_BITS(inode->i_sb);
        const long direct_blocks = EXT2_NDIR_BLOCKS,
                indirect_blocks = ptrs,
                double_blocks = (1 << (ptrs_bits * 2));
        int n = 0;
        int final = 0;

        if (i_block < 0) {
                ext2_warning (inode->i_sb, "ext2_block_to_path", "block < 0");
        } else if (i_block < direct_blocks) {
                offsets[n++] = i_block;
                final = direct_blocks;
        } else if ( (i_block -= direct_blocks) < indirect_blocks) {
                offsets[n++] = EXT2_IND_BLOCK;
                offsets[n++] = i_block;
                final = ptrs;
        } else if ((i_block -= indirect_blocks) < double_blocks) {
                offsets[n++] = EXT2_DIND_BLOCK;
                offsets[n++] = i_block >> ptrs_bits;
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
                offsets[n++] = EXT2_TIND_BLOCK;
                offsets[n++] = i_block >> (ptrs_bits * 2);
                offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else {
                ext2_warning (inode->i_sb, "ext2_block_to_path", "block > big");
        }
        if (boundary)
                *boundary = (i_block & (ptrs - 1)) == (final - 1);
        return n;
}

/**
 *      ext2_get_branch - read the chain of indirect blocks leading to data
 *      @inode: inode in question
 *      @depth: depth of the chain (1 - direct pointer, etc.)
 *      @offsets: offsets of pointers in inode/indirect blocks
 *      @chain: place to store the result
 *      @err: here we store the error value
 *
 *      Function fills the array of triples <key, p, bh> and returns %NULL
 *      if everything went OK or the pointer to the last filled triple
 *      (incomplete one) otherwise. Upon the return chain[i].key contains
 *      the number of (i+1)-th block in the chain (as it is stored in memory,
 *      i.e. little-endian 32-bit), chain[i].p contains the address of that
 *      number (it points into struct inode for i==0 and into the bh->b_data
 *      for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *      block for i>0 and NULL for i==0. In other words, it holds the block
 *      numbers of the chain, addresses they were taken from (and where we can
 *      verify that chain did not change) and buffer_heads hosting these
 *      numbers.
 *
 *      Function stops when it stumbles upon zero pointer (absent block)
 *              (pointer to last triple returned, *@err == 0)
 *      or when it gets an IO error reading an indirect block
 *              (ditto, *@err == -EIO)
 *      or when it notices that chain had been changed while it was reading
 *              (ditto, *@err == -EAGAIN)
 *      or when it reads all @depth-1 indirect blocks successfully and finds
 *      the whole chain, all way to the data (returns %NULL, *err == 0).
 */
static Indirect *ext2_get_branch(struct inode *inode,
                                 int depth,
                                 int *offsets,
                                 Indirect chain[4],
                                 int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;

        *err = 0;
        /* i_data is not going away, no lock needed */
        add_chain (chain, NULL, EXT2_I(inode)->i_data + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                bh = sb_bread(sb, le32_to_cpu(p->key));
                if (!bh)
                        goto failure;
                read_lock(&EXT2_I(inode)->i_meta_lock);
                if (!verify_chain(chain, p))
                        goto changed;
                add_chain(++p, bh, (u32*)bh->b_data + *++offsets);
                read_unlock(&EXT2_I(inode)->i_meta_lock);
                if (!p->key)
                        goto no_block;
        }
        return NULL;

changed:
        read_unlock(&EXT2_I(inode)->i_meta_lock);
        brelse(bh);
        *err = -EAGAIN;
        goto no_block;
failure:
        *err = -EIO;
no_block:
        return p;
}

/**
 *      ext2_find_near - find a place for allocation with sufficient locality
 *      @inode: owner
 *      @ind: descriptor of indirect block.
 *
 *      This function returns the prefered place for block allocation.
 *      It is used when heuristic for sequential allocation fails.
 *      Rules are:
 *        + if there is a block to the left of our position - allocate near it.
 *        + if pointer will live in indirect block - allocate near that block.
 *        + if pointer will live in inode - allocate in the same cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *      Caller must make sure that @ind is valid and will stay that way.
 */

static unsigned long ext2_find_near(struct inode *inode, Indirect *ind)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        u32 *start = ind->bh ? (u32*) ind->bh->b_data : ei->i_data;
        u32 *p;
        unsigned long bg_start;
        unsigned long colour;

        /* Try to find previous block */
        for (p = ind->p - 1; p >= start; p--)
                if (*p)
                        return le32_to_cpu(*p);

        /* No such thing, so let's try location of indirect block */
        if (ind->bh)
                return ind->bh->b_blocknr;

        /*
         * It is going to be refered from inode itself? OK, just put it into
         * the same cylinder group then.
         */
        bg_start = (ei->i_block_group * EXT2_BLOCKS_PER_GROUP(inode->i_sb)) +
                le32_to_cpu(EXT2_SB(inode->i_sb)->s_es->s_first_data_block);
        colour = (current->pid % 16) *
                        (EXT2_BLOCKS_PER_GROUP(inode->i_sb) / 16);
        return bg_start + colour;
}

/**
 *      ext2_find_goal - find a prefered place for allocation.
 *      @inode: owner
 *      @block:  block we want
 *      @chain:  chain of indirect blocks
 *      @partial: pointer to the last triple within a chain
 *      @goal:  place to store the result.
 *
 *      Normally this function find the prefered place for block allocation,
 *      stores it in *@goal and returns zero. If the branch had been changed
 *      under us we return -EAGAIN.
 */

static inline int ext2_find_goal(struct inode *inode,
                                 long block,
                                 Indirect chain[4],
                                 Indirect *partial,
                                 unsigned long *goal)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        write_lock(&ei->i_meta_lock);
        if (block == ei->i_next_alloc_block + 1) {
                ei->i_next_alloc_block++;
                ei->i_next_alloc_goal++;
        } 
        if (verify_chain(chain, partial)) {
                /*
                 * try the heuristic for sequential allocation,
                 * failing that at least try to get decent locality.
                 */
                if (block == ei->i_next_alloc_block)
                        *goal = ei->i_next_alloc_goal;
                if (!*goal)
                        *goal = ext2_find_near(inode, partial);
                write_unlock(&ei->i_meta_lock);
                return 0;
        }
        write_unlock(&ei->i_meta_lock);
        return -EAGAIN;
}

/**
 *      ext2_alloc_branch - allocate and set up a chain of blocks.
 *      @inode: owner
 *      @num: depth of the chain (number of blocks to allocate)
 *      @offsets: offsets (in the blocks) to store the pointers to next.
 *      @branch: place to store the chain in.
 *
 *      This function allocates @num blocks, zeroes out all but the last one,
 *      links them into chain and (if we are synchronous) writes them to disk.
 *      In other words, it prepares a branch that can be spliced onto the
 *      inode. It stores the information about that chain in the branch[], in
 *      the same format as ext2_get_branch() would do. We are calling it after
 *      we had read the existing part of chain and partial points to the last
 *      triple of that (one with zero ->key). Upon the exit we have the same
 *      picture as after the successful ext2_get_block(), excpet that in one
 *      place chain is disconnected - *branch->p is still zero (we did not
 *      set the last link), but branch->key contains the number that should
 *      be placed into *branch->p to fill that gap.
 *
 *      If allocation fails we free all blocks we've allocated (and forget
 *      their buffer_heads) and return the error value the from failed
 *      ext2_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *      as described above and return 0.
 */

static int ext2_alloc_branch(struct inode *inode,
                             int num,
                             unsigned long goal,
                             int *offsets,
                             Indirect *branch)
{
        int blocksize = inode->i_sb->s_blocksize;
        int n = 0;
        int err;
        int i;
        int parent = ext2_alloc_block(inode, goal, &err);

        branch[0].key = cpu_to_le32(parent);
        if (parent) for (n = 1; n < num; n++) {
                struct buffer_head *bh;
                /* Allocate the next block */
                int nr = ext2_alloc_block(inode, parent, &err);
                if (!nr)
                        break;
                branch[n].key = cpu_to_le32(nr);
                /*
                 * Get buffer_head for parent block, zero it out and set 
                 * the pointer to new one, then send parent to disk.
                 */
                bh = sb_getblk(inode->i_sb, parent);
                lock_buffer(bh);
                memset(bh->b_data, 0, blocksize);
                branch[n].bh = bh;
                branch[n].p = (u32*) bh->b_data + offsets[n];
                *branch[n].p = branch[n].key;
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
                mark_buffer_dirty_inode(bh, inode);
                /* We used to sync bh here if IS_SYNC(inode).
                 * But we now rely upon generic_osync_inode()
                 * and b_inode_buffers.  But not for directories.
                 */
                if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
                        sync_dirty_buffer(bh);
                parent = nr;
        }
        if (n == num)
                return 0;

        /* Allocation failed, free what we already allocated */
        for (i = 1; i < n; i++)
                bforget(branch[i].bh);
        for (i = 0; i < n; i++)
                ext2_free_blocks(inode, le32_to_cpu(branch[i].key), 1);
        return err;
}

/**
 *      ext2_splice_branch - splice the allocated branch onto inode.
 *      @inode: owner
 *      @block: (logical) number of block we are adding
 *      @chain: chain of indirect blocks (with a missing link - see
 *              ext2_alloc_branch)
 *      @where: location of missing link
 *      @num:   number of blocks we are adding
 *
 *      This function verifies that chain (up to the missing link) had not
 *      changed, fills the missing link and does all housekeeping needed in
 *      inode (->i_blocks, etc.). In case of success we end up with the full
 *      chain to new block and return 0. Otherwise (== chain had been changed)
 *      we free the new blocks (forgetting their buffer_heads, indeed) and
 *      return -EAGAIN.
 */

static inline int ext2_splice_branch(struct inode *inode,
                                     long block,
                                     Indirect chain[4],
                                     Indirect *where,
                                     int num)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        int i;

        /* Verify that place we are splicing to is still there and vacant */

        write_lock(&ei->i_meta_lock);
        if (!verify_chain(chain, where-1) || *where->p)
                goto changed;

        /* That's it */

        *where->p = where->key;
        ei->i_next_alloc_block = block;
        ei->i_next_alloc_goal = le32_to_cpu(where[num-1].key);

        write_unlock(&ei->i_meta_lock);

        /* We are done with atomic stuff, now do the rest of housekeeping */

        inode->i_ctime = CURRENT_TIME;

        /* had we spliced it onto indirect block? */
        if (where->bh)
                mark_buffer_dirty_inode(where->bh, inode);

        mark_inode_dirty(inode);
        return 0;

changed:
        write_unlock(&ei->i_meta_lock);
        for (i = 1; i < num; i++)
                bforget(where[i].bh);
        for (i = 0; i < num; i++)
                ext2_free_blocks(inode, le32_to_cpu(where[i].key), 1);
        return -EAGAIN;
}

/*
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 */

static int ext2_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
{
        int err = -EIO;
        int offsets[4];
        Indirect chain[4];
        Indirect *partial;
        unsigned long goal;
        int left;
        int boundary = 0;
        int depth = ext2_block_to_path(inode, iblock, offsets, &boundary);

        if (depth == 0)
                goto out;

reread:
        partial = ext2_get_branch(inode, depth, offsets, chain, &err);

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
got_it:
                map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
                if (boundary)
                        set_buffer_boundary(bh_result);
                /* Clean up and exit */
                partial = chain+depth-1; /* the whole chain */
                goto cleanup;
        }

        /* Next simple case - plain lookup or failed read of indirect block */
        if (!create || err == -EIO) {
cleanup:
                while (partial > chain) {
                        brelse(partial->bh);
                        partial--;
                }
out:
                return err;
        }

        /*
         * Indirect block might be removed by truncate while we were
         * reading it. Handling of that case (forget what we've got and
         * reread) is taken out of the main path.
         */
        if (err == -EAGAIN)
                goto changed;

        goal = 0;
        if (ext2_find_goal(inode, iblock, chain, partial, &goal) < 0)
                goto changed;

        left = (chain + depth) - partial;
        err = ext2_alloc_branch(inode, left, goal,
                                        offsets+(partial-chain), partial);
        if (err)
                goto cleanup;

        if (ext2_splice_branch(inode, iblock, chain, partial, left) < 0)
                goto changed;

        set_buffer_new(bh_result);
        goto got_it;

changed:
        while (partial > chain) {
                brelse(partial->bh);
                partial--;
        }
        goto reread;
}

static int ext2_writepage(struct page *page, struct writeback_control *wbc)
{
        return block_write_full_page(page, ext2_get_block, wbc);
}

static int ext2_readpage(struct file *file, struct page *page)
{
        return mpage_readpage(page, ext2_get_block);
}

static int
ext2_readpages(struct file *file, struct address_space *mapping,
                struct list_head *pages, unsigned nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, ext2_get_block);
}

static int
ext2_prepare_write(struct file *file, struct page *page,
                        unsigned from, unsigned to)
{
        return block_prepare_write(page,from,to,ext2_get_block);
}

static int
ext2_nobh_prepare_write(struct file *file, struct page *page,
                        unsigned from, unsigned to)
{
        return nobh_prepare_write(page,from,to,ext2_get_block);
}

static sector_t ext2_bmap(struct address_space *mapping, sector_t block)
{
        return generic_block_bmap(mapping,block,ext2_get_block);
}

static int
ext2_get_blocks(struct inode *inode, sector_t iblock, unsigned long max_blocks,
                        struct buffer_head *bh_result, int create)
{
        int ret;

        ret = ext2_get_block(inode, iblock, bh_result, create);
        if (ret == 0)
                bh_result->b_size = (1 << inode->i_blkbits);
        return ret;
}

static ssize_t
ext2_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                        loff_t offset, unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;

        return blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
                                offset, nr_segs, ext2_get_blocks, NULL);
}

static int
ext2_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        return mpage_writepages(mapping, wbc, ext2_get_block);
}

struct address_space_operations ext2_aops = {
        .readpage               = ext2_readpage,
        .readpages              = ext2_readpages,
        .writepage              = ext2_writepage,
        .sync_page              = block_sync_page,
        .prepare_write          = ext2_prepare_write,
        .commit_write           = generic_commit_write,
        .bmap                   = ext2_bmap,
        .direct_IO              = ext2_direct_IO,
        .writepages             = ext2_writepages,
};

struct address_space_operations ext2_nobh_aops = {
        .readpage               = ext2_readpage,
        .readpages              = ext2_readpages,
        .writepage              = ext2_writepage,
        .sync_page              = block_sync_page,
        .prepare_write          = ext2_nobh_prepare_write,
        .commit_write           = nobh_commit_write,
        .bmap                   = ext2_bmap,
        .direct_IO              = ext2_direct_IO,
        .writepages             = ext2_writepages,
};

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(u32 *p, u32 *q)
{
        while (p < q)
                if (*p++)
                        return 0;
        return 1;
}

/**
 *      ext2_find_shared - find the indirect blocks for partial truncation.
 *      @inode:   inode in question
 *      @depth:   depth of the affected branch
 *      @offsets: offsets of pointers in that branch (see ext2_block_to_path)
 *      @chain:   place to store the pointers to partial indirect blocks
 *      @top:     place to the (detached) top of branch
 *
 *      This is a helper function used by ext2_truncate().
 *
 *      When we do truncate() we may have to clean the ends of several indirect
 *      blocks but leave the blocks themselves alive. Block is partially
 *      truncated if some data below the new i_size is refered from it (and
 *      it is on the path to the first completely truncated data block, indeed).
 *      We have to free the top of that path along with everything to the right
 *      of the path. Since no allocation past the truncation point is possible
 *      until ext2_truncate() finishes, we may safely do the latter, but top
 *      of branch may require special attention - pageout below the truncation
 *      point might try to populate it.
 *
 *      We atomically detach the top of branch from the tree, store the block
 *      number of its root in *@top, pointers to buffer_heads of partially
 *      truncated blocks - in @chain[].bh and pointers to their last elements
 *      that should not be removed - in @chain[].p. Return value is the pointer
 *      to last filled element of @chain.
 *
 *      The work left to caller to do the actual freeing of subtrees:
 *              a) free the subtree starting from *@top
 *              b) free the subtrees whose roots are stored in
 *                      (@chain[i].p+1 .. end of @chain[i].bh->b_data)
 *              c) free the subtrees growing from the inode past the @chain[0].p
 *                      (no partially truncated stuff there).
 */

static Indirect *ext2_find_shared(struct inode *inode,
                                int depth,
                                int offsets[4],
                                Indirect chain[4],
                                u32 *top)
{
        Indirect *partial, *p;
        int k, err;

        *top = 0;
        for (k = depth; k > 1 && !offsets[k-1]; k--)
                ;
        partial = ext2_get_branch(inode, k, offsets, chain, &err);
        if (!partial)
                partial = chain + k-1;
        /*
         * If the branch acquired continuation since we've looked at it -
         * fine, it should all survive and (new) top doesn't belong to us.
         */
        write_lock(&EXT2_I(inode)->i_meta_lock);
        if (!partial->key && *partial->p) {
                write_unlock(&EXT2_I(inode)->i_meta_lock);
                goto no_top;
        }
        for (p=partial; p>chain && all_zeroes((u32*)p->bh->b_data,p->p); p--)
                ;
        /*
         * OK, we've found the last block that must survive. The rest of our
         * branch should be detached before unlocking. However, if that rest
         * of branch is all ours and does not grow immediately from the inode
         * it's easier to cheat and just decrement partial->p.
         */
        if (p == chain + k - 1 && p > chain) {
                p->p--;
        } else {
                *top = *p->p;
                *p->p = 0;
        }
        write_unlock(&EXT2_I(inode)->i_meta_lock);

        while(partial > p)
        {
                brelse(partial->bh);
                partial--;
        }
no_top:
        return partial;
}

/**
 *      ext2_free_data - free a list of data blocks
 *      @inode: inode we are dealing with
 *      @p:     array of block numbers
 *      @q:     points immediately past the end of array
 *
 *      We are freeing all blocks refered from that array (numbers are
 *      stored as little-endian 32-bit) and updating @inode->i_blocks
 *      appropriately.
 */
static inline void ext2_free_data(struct inode *inode, u32 *p, u32 *q)
{
        unsigned long block_to_free = 0, count = 0;
        unsigned long nr;

        for ( ; p < q ; p++) {
                nr = le32_to_cpu(*p);
                if (nr) {
                        *p = 0;
                        /* accumulate blocks to free if they're contiguous */
                        if (count == 0)
                                goto free_this;
                        else if (block_to_free == nr - count)
                                count++;
                        else {
                                mark_inode_dirty(inode);
                                ext2_free_blocks (inode, block_to_free, count);
                        free_this:
                                block_to_free = nr;
                                count = 1;
                        }
                }
        }
        if (count > 0) {
                mark_inode_dirty(inode);
                ext2_free_blocks (inode, block_to_free, count);
        }
}

/**
 *      ext2_free_branches - free an array of branches
 *      @inode: inode we are dealing with
 *      @p:     array of block numbers
 *      @q:     pointer immediately past the end of array
 *      @depth: depth of the branches to free
 *
 *      We are freeing all blocks refered from these branches (numbers are
 *      stored as little-endian 32-bit) and updating @inode->i_blocks
 *      appropriately.
 */
static void ext2_free_branches(struct inode *inode, u32 *p, u32 *q, int depth)
{
        struct buffer_head * bh;
        unsigned long nr;

        if (depth--) {
                int addr_per_block = EXT2_ADDR_PER_BLOCK(inode->i_sb);
                for ( ; p < q ; p++) {
                        nr = le32_to_cpu(*p);
                        if (!nr)
                                continue;
                        *p = 0;
                        bh = sb_bread(inode->i_sb, nr);
                        /*
                         * A read failure? Report error and clear slot
                         * (should be rare).
                         */ 
                        if (!bh) {
                                ext2_error(inode->i_sb, "ext2_free_branches",
                                        "Read failure, inode=%ld, block=%ld",
                                        inode->i_ino, nr);
                                continue;
                        }
                        ext2_free_branches(inode,
                                           (u32*)bh->b_data,
                                           (u32*)bh->b_data + addr_per_block,
                                           depth);
                        bforget(bh);
                        ext2_free_blocks(inode, nr, 1);
                        mark_inode_dirty(inode);
                }
        } else
                ext2_free_data(inode, p, q);
}

static void ext2_truncate_nocheck(struct inode * inode)
{
        u32 *i_data = EXT2_I(inode)->i_data;
        int addr_per_block = EXT2_ADDR_PER_BLOCK(inode->i_sb);
        int offsets[4];
        Indirect chain[4];
        Indirect *partial;
        int nr = 0;
        int n;
        long iblock;
        unsigned blocksize;

        if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
            S_ISLNK(inode->i_mode)))
                return;
        if (ext2_inode_is_fast_symlink(inode))
                return;

        ext2_discard_prealloc(inode);

        blocksize = inode->i_sb->s_blocksize;
        iblock = (inode->i_size + blocksize-1)
                                        >> EXT2_BLOCK_SIZE_BITS(inode->i_sb);

        if (test_opt(inode->i_sb, NOBH))
                nobh_truncate_page(inode->i_mapping, inode->i_size);
        else
                block_truncate_page(inode->i_mapping,
                                inode->i_size, ext2_get_block);

        n = ext2_block_to_path(inode, iblock, offsets, NULL);
        if (n == 0)
                return;

        if (n == 1) {
                ext2_free_data(inode, i_data+offsets[0],
                                        i_data + EXT2_NDIR_BLOCKS);
                goto do_indirects;
        }

        partial = ext2_find_shared(inode, n, offsets, chain, &nr);
        /* Kill the top of shared branch (already detached) */
        if (nr) {
                if (partial == chain)
                        mark_inode_dirty(inode);
                else
                        mark_buffer_dirty_inode(partial->bh, inode);
                ext2_free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
        }
        /* Clear the ends of indirect blocks on the shared branch */
        while (partial > chain) {
                ext2_free_branches(inode,
                                   partial->p + 1,
                                   (u32*)partial->bh->b_data + addr_per_block,
                                   (chain+n-1) - partial);
                mark_buffer_dirty_inode(partial->bh, inode);
                brelse (partial->bh);
                partial--;
        }
do_indirects:
        /* Kill the remaining (whole) subtrees */
        switch (offsets[0]) {
                default:
                        nr = i_data[EXT2_IND_BLOCK];
                        if (nr) {
                                i_data[EXT2_IND_BLOCK] = 0;
                                mark_inode_dirty(inode);
                                ext2_free_branches(inode, &nr, &nr+1, 1);
                        }
                case EXT2_IND_BLOCK:
                        nr = i_data[EXT2_DIND_BLOCK];
                        if (nr) {
                                i_data[EXT2_DIND_BLOCK] = 0;
                                mark_inode_dirty(inode);
                                ext2_free_branches(inode, &nr, &nr+1, 2);
                        }
                case EXT2_DIND_BLOCK:
                        nr = i_data[EXT2_TIND_BLOCK];
                        if (nr) {
                                i_data[EXT2_TIND_BLOCK] = 0;
                                mark_inode_dirty(inode);
                                ext2_free_branches(inode, &nr, &nr+1, 3);
                        }
                case EXT2_TIND_BLOCK:
                        ;
        }
        inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        if (inode_needs_sync(inode)) {
                sync_mapping_buffers(inode->i_mapping);
                ext2_sync_inode (inode);
        } else {
                mark_inode_dirty(inode);
        }
}

static struct ext2_inode *ext2_get_inode(struct super_block *sb, ino_t ino,
                                        struct buffer_head **p)
{
        struct buffer_head * bh;
        unsigned long block_group;
        unsigned long block;
        unsigned long offset;
        struct ext2_group_desc * gdp;

        *p = NULL;
        if ((ino != EXT2_ROOT_INO && ino < EXT2_FIRST_INO(sb)) ||
            ino > le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count))
                goto Einval;

        block_group = (ino - 1) / EXT2_INODES_PER_GROUP(sb);
        gdp = ext2_get_group_desc(sb, block_group, &bh);
        if (!gdp)
                goto Egdp;
        /*
         * Figure out the offset within the block group inode table
         */
        offset = ((ino - 1) % EXT2_INODES_PER_GROUP(sb)) * EXT2_INODE_SIZE(sb);
        block = le32_to_cpu(gdp->bg_inode_table) +
                (offset >> EXT2_BLOCK_SIZE_BITS(sb));
        if (!(bh = sb_bread(sb, block)))
                goto Eio;

        *p = bh;
        offset &= (EXT2_BLOCK_SIZE(sb) - 1);
        return (struct ext2_inode *) (bh->b_data + offset);

Einval:
        ext2_error(sb, "ext2_get_inode", "bad inode number: %lu",
                   (unsigned long) ino);
        return ERR_PTR(-EINVAL);
Eio:
        ext2_error(sb, "ext2_get_inode",
                   "unable to read inode block - inode=%lu, block=%lu",
                   (unsigned long) ino, block);
Egdp:
        return ERR_PTR(-EIO);
}

void ext2_truncate (struct inode * inode)
{
        if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
                return;
        ext2_truncate_nocheck(inode);
}

void ext2_set_inode_flags(struct inode *inode)
{
        unsigned int flags = EXT2_I(inode)->i_flags;

        inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
        if (flags & EXT2_SYNC_FL)
                inode->i_flags |= S_SYNC;
        if (flags & EXT2_APPEND_FL)
                inode->i_flags |= S_APPEND;
        if (flags & EXT2_IMMUTABLE_FL)
                inode->i_flags |= S_IMMUTABLE;
        if (flags & EXT2_IUNLINK_FL)
                inode->i_flags |= S_IUNLINK;
        if (flags & EXT2_BARRIER_FL)
                inode->i_flags |= S_BARRIER;
        if (flags & EXT2_NOATIME_FL)
                inode->i_flags |= S_NOATIME;
        if (flags & EXT2_DIRSYNC_FL)
                inode->i_flags |= S_DIRSYNC;
}

void ext2_read_inode (struct inode * inode)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        ino_t ino = inode->i_ino;
        struct buffer_head * bh;
        struct ext2_inode * raw_inode = ext2_get_inode(inode->i_sb, ino, &bh);
        uid_t uid;
        gid_t gid;
        int n;

#ifdef CONFIG_EXT2_FS_POSIX_ACL
        ei->i_acl = EXT2_ACL_NOT_CACHED;
        ei->i_default_acl = EXT2_ACL_NOT_CACHED;
#endif
        if (IS_ERR(raw_inode))
                goto bad_inode;

        inode->i_mode = le16_to_cpu(raw_inode->i_mode);
        uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
        gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
        if (!(test_opt (inode->i_sb, NO_UID32))) {
                uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
                gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
        }
        inode->i_uid = INOXID_UID(uid, gid);
        inode->i_gid = INOXID_GID(uid, gid);
        if (inode->i_sb->s_flags & MS_TAGXID)
                inode->i_xid = INOXID_XID(uid, gid, le16_to_cpu(raw_inode->i_raw_xid));

        inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
        inode->i_size = le32_to_cpu(raw_inode->i_size);
        inode->i_atime.tv_sec = le32_to_cpu(raw_inode->i_atime);
        inode->i_ctime.tv_sec = le32_to_cpu(raw_inode->i_ctime);
        inode->i_mtime.tv_sec = le32_to_cpu(raw_inode->i_mtime);
        inode->i_atime.tv_nsec = inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec = 0;
        ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
        /* We now have enough fields to check if the inode was active or not.
         * This is needed because nfsd might try to access dead inodes
         * the test is that same one that e2fsck uses
         * NeilBrown 1999oct15
         */
        if (inode->i_nlink == 0 && (inode->i_mode == 0 || ei->i_dtime)) {
                /* this inode is deleted */
                brelse (bh);
                goto bad_inode;
        }
        inode->i_blksize = PAGE_SIZE;   /* This is the optimal IO size (for stat), not the fs block size */
        inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);
        ei->i_flags = le32_to_cpu(raw_inode->i_flags);
        ei->i_faddr = le32_to_cpu(raw_inode->i_faddr);
        ei->i_frag_no = raw_inode->i_frag;
        ei->i_frag_size = raw_inode->i_fsize;
        ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
        ei->i_dir_acl = 0;
        if (S_ISREG(inode->i_mode))
                inode->i_size |= ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
        else
                ei->i_dir_acl = le32_to_cpu(raw_inode->i_dir_acl);
        ei->i_dtime = 0;
        inode->i_generation = le32_to_cpu(raw_inode->i_generation);
        ei->i_state = 0;
        ei->i_next_alloc_block = 0;
        ei->i_next_alloc_goal = 0;
        ei->i_prealloc_count = 0;
        ei->i_block_group = (ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
        ei->i_dir_start_lookup = 0;

        /*
         * NOTE! The in-memory inode i_data array is in little-endian order
         * even on big-endian machines: we do NOT byteswap the block numbers!
         */
        for (n = 0; n < EXT2_N_BLOCKS; n++)
                ei->i_data[n] = raw_inode->i_block[n];

        if (S_ISREG(inode->i_mode)) {
                inode->i_op = &ext2_file_inode_operations;
                inode->i_fop = &ext2_file_operations;
                if (test_opt(inode->i_sb, NOBH))
                        inode->i_mapping->a_ops = &ext2_nobh_aops;
                else
                        inode->i_mapping->a_ops = &ext2_aops;
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_op = &ext2_dir_inode_operations;
                inode->i_fop = &ext2_dir_operations;
                if (test_opt(inode->i_sb, NOBH))
                        inode->i_mapping->a_ops = &ext2_nobh_aops;
                else
                        inode->i_mapping->a_ops = &ext2_aops;
        } else if (S_ISLNK(inode->i_mode)) {
                if (ext2_inode_is_fast_symlink(inode))
                        inode->i_op = &ext2_fast_symlink_inode_operations;
                else {
                        inode->i_op = &ext2_symlink_inode_operations;
                        if (test_opt(inode->i_sb, NOBH))
                                inode->i_mapping->a_ops = &ext2_nobh_aops;
                        else
                                inode->i_mapping->a_ops = &ext2_aops;
                }
        } else {
                inode->i_op = &ext2_special_inode_operations;
                if (raw_inode->i_block[0])
                        init_special_inode(inode, inode->i_mode,
                           old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
                else 
                        init_special_inode(inode, inode->i_mode,
                           new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
        }
        brelse (bh);
        ext2_set_inode_flags(inode);
        return;
        
bad_inode:
        make_bad_inode(inode);
        return;
}

static int ext2_update_inode(struct inode * inode, int do_sync)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        struct super_block *sb = inode->i_sb;
        ino_t ino = inode->i_ino;
        uid_t uid = XIDINO_UID(inode->i_uid, inode->i_xid);
        gid_t gid = XIDINO_GID(inode->i_gid, inode->i_xid);
        struct buffer_head * bh;
        struct ext2_inode * raw_inode = ext2_get_inode(sb, ino, &bh);
        int n;
        int err = 0;

        if (IS_ERR(raw_inode))
                return -EIO;

        /* For fields not not tracking in the in-memory inode,
         * initialise them to zero for new inodes. */
        if (ei->i_state & EXT2_STATE_NEW)
                memset(raw_inode, 0, EXT2_SB(sb)->s_inode_size);

        raw_inode->i_mode = cpu_to_le16(inode->i_mode);
        if (!(test_opt(sb, NO_UID32))) {
                raw_inode->i_uid_low = cpu_to_le16(low_16_bits(uid));
                raw_inode->i_gid_low = cpu_to_le16(low_16_bits(gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
                if (!ei->i_dtime) {
                        raw_inode->i_uid_high = cpu_to_le16(high_16_bits(uid));
                        raw_inode->i_gid_high = cpu_to_le16(high_16_bits(gid));
                } else {
                        raw_inode->i_uid_high = 0;
                        raw_inode->i_gid_high = 0;
                }
        } else {
                raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(uid));
                raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(gid));
                raw_inode->i_uid_high = 0;
                raw_inode->i_gid_high = 0;
        }
#ifdef CONFIG_INOXID_GID32
        raw_inode->i_raw_xid = cpu_to_le16(inode->i_xid);
#endif
        raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
        raw_inode->i_size = cpu_to_le32(inode->i_size);
        raw_inode->i_atime = cpu_to_le32(inode->i_atime.tv_sec);
        raw_inode->i_ctime = cpu_to_le32(inode->i_ctime.tv_sec);
        raw_inode->i_mtime = cpu_to_le32(inode->i_mtime.tv_sec);

        raw_inode->i_blocks = cpu_to_le32(inode->i_blocks);
        raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
        raw_inode->i_flags = cpu_to_le32(ei->i_flags);
        raw_inode->i_faddr = cpu_to_le32(ei->i_faddr);
        raw_inode->i_frag = ei->i_frag_no;
        raw_inode->i_fsize = ei->i_frag_size;
        raw_inode->i_file_acl = cpu_to_le32(ei->i_file_acl);
        if (!S_ISREG(inode->i_mode))
                raw_inode->i_dir_acl = cpu_to_le32(ei->i_dir_acl);
        else {
                raw_inode->i_size_high = cpu_to_le32(inode->i_size >> 32);
                if (inode->i_size > 0x7fffffffULL) {
                        if (!EXT2_HAS_RO_COMPAT_FEATURE(sb,
                                        EXT2_FEATURE_RO_COMPAT_LARGE_FILE) ||
                            EXT2_SB(sb)->s_es->s_rev_level ==
                                        cpu_to_le32(EXT2_GOOD_OLD_REV)) {
                               /* If this is the first large file
                                * created, add a flag to the superblock.
                                */
                                lock_kernel();
                                ext2_update_dynamic_rev(sb);
                                EXT2_SET_RO_COMPAT_FEATURE(sb,
                                        EXT2_FEATURE_RO_COMPAT_LARGE_FILE);
                                unlock_kernel();
                                ext2_write_super(sb);
                        }
                }
        }
        
        raw_inode->i_generation = cpu_to_le32(inode->i_generation);
        if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                if (old_valid_dev(inode->i_rdev)) {
                        raw_inode->i_block[0] =
                                cpu_to_le32(old_encode_dev(inode->i_rdev));
                        raw_inode->i_block[1] = 0;
                } else {
                        raw_inode->i_block[0] = 0;
                        raw_inode->i_block[1] =
                                cpu_to_le32(new_encode_dev(inode->i_rdev));
                        raw_inode->i_block[2] = 0;
                }
        } else for (n = 0; n < EXT2_N_BLOCKS; n++)
                raw_inode->i_block[n] = ei->i_data[n];
        mark_buffer_dirty(bh);
        if (do_sync) {
                sync_dirty_buffer(bh);
                if (buffer_req(bh) && !buffer_uptodate(bh)) {
                        printk ("IO error syncing ext2 inode [%s:%08lx]\n",
                                sb->s_id, (unsigned long) ino);
                        err = -EIO;
                }
        }
        ei->i_state &= ~EXT2_STATE_NEW;
        brelse (bh);
        return err;
}

void ext2_write_inode(struct inode *inode, int wait)
{
        ext2_update_inode(inode, wait);
}

int ext2_sync_inode(struct inode *inode)
{
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = 0,       /* sys_fsync did this */
        };
        return sync_inode(inode, &wbc);
}

int ext2_setattr_flags(struct inode *inode, unsigned int flags)
{
        unsigned int oldflags, newflags;

        oldflags = EXT2_I(inode)->i_flags;
        newflags = oldflags &
                ~(EXT2_IMMUTABLE_FL | EXT2_IUNLINK_FL | EXT2_BARRIER_FL);       
        if (flags & ATTR_FLAG_IMMUTABLE)
                newflags |= EXT2_IMMUTABLE_FL;
        if (flags & ATTR_FLAG_IUNLINK)
                newflags |= EXT2_IUNLINK_FL;
        if (flags & ATTR_FLAG_BARRIER)
                newflags |= EXT2_BARRIER_FL;

        if (oldflags ^ newflags) {
                EXT2_I(inode)->i_flags = newflags;
                inode->i_ctime = CURRENT_TIME;
        }
        return 0;
}

int ext2_setattr(struct dentry *dentry, struct iattr *iattr)
{
        struct inode *inode = dentry->d_inode;
        int error;

        error = inode_change_ok(inode, iattr);
        if (error)
                return error;
        if ((iattr->ia_valid & ATTR_UID && iattr->ia_uid != inode->i_uid) ||
            (iattr->ia_valid & ATTR_GID && iattr->ia_gid != inode->i_gid) ||
            (iattr->ia_valid & ATTR_XID && iattr->ia_xid != inode->i_xid)) {
                error = DQUOT_TRANSFER(inode, iattr) ? -EDQUOT : 0;
                if (error)
                        return error;
        }
        if (iattr->ia_valid & ATTR_ATTR_FLAG)
                ext2_setattr_flags(inode, iattr->ia_attr_flags);

        inode_setattr(inode, iattr);
        if (iattr->ia_valid & ATTR_MODE)
                error = ext2_acl_chmod(inode);
        return error;
}