FreeBSD/Linux Kernel Cross Reference
sys/fs/ext3/inode.c

     /*
      *  linux/fs/ext3/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@redhat.com), 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 ext3_get_block() by Al Viro, 2000
     */
    
    #include <linux/fs.h>
    #include <linux/sched.h>
    #include <linux/ext3_jbd.h>
    #include <linux/jbd.h>
    #include <linux/locks.h>
    #include <linux/smp_lock.h>
    #include <linux/highuid.h>
    #include <linux/quotaops.h>
    #include <linux/module.h>
    
    /*
     * SEARCH_FROM_ZERO forces each block allocation to search from the start
     * of the filesystem.  This is to force rapid reallocation of recently-freed
     * blocks.  The file fragmentation is horrendous.
     */
    #undef SEARCH_FROM_ZERO
    
    /* The ext3 forget function must perform a revoke if we are freeing data
     * which has been journaled.  Metadata (eg. indirect blocks) must be
     * revoked in all cases. 
     *
     * "bh" may be NULL: a metadata block may have been freed from memory
     * but there may still be a record of it in the journal, and that record
     * still needs to be revoked.
     */
    
    static int ext3_forget(handle_t *handle, int is_metadata,
                           struct inode *inode, struct buffer_head *bh,
                           int blocknr)
    {
            int err;
    
            BUFFER_TRACE(bh, "enter");
    
            jbd_debug(4, "forgetting bh %p: is_metadata = %d, mode %o, "
                      "data mode %lx\n",
                      bh, is_metadata, inode->i_mode,
                      test_opt(inode->i_sb, DATA_FLAGS));
            
            /* Never use the revoke function if we are doing full data
             * journaling: there is no need to, and a V1 superblock won't
             * support it.  Otherwise, only skip the revoke on un-journaled
             * data blocks. */
    
            if (test_opt(inode->i_sb, DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ||
                (!is_metadata && !ext3_should_journal_data(inode))) {
                    if (bh) {
                            BUFFER_TRACE(bh, "call journal_forget");
                            ext3_journal_forget(handle, bh);
                    }
                    return 0;
            }
    
            /*
             * data!=journal && (is_metadata || should_journal_data(inode))
             */
            BUFFER_TRACE(bh, "call ext3_journal_revoke");
            err = ext3_journal_revoke(handle, blocknr, bh);
            if (err)
                    ext3_abort(inode->i_sb, __FUNCTION__,
                               "error %d when attempting revoke", err);
            BUFFER_TRACE(bh, "exit");
            return err;
    }
    
    /*
     * Work out how many blocks we need to progress with the next chunk of a
     * truncate transaction.
     */
    
    static unsigned long blocks_for_truncate(struct inode *inode) 
    {
            unsigned long needed;
            
            needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);
   
           /* Give ourselves just enough room to cope with inodes in which
            * i_blocks is corrupt: we've seen disk corruptions in the past
            * which resulted in random data in an inode which looked enough
            * like a regular file for ext3 to try to delete it.  Things
            * will go a bit crazy if that happens, but at least we should
            * try not to panic the whole kernel. */
           if (needed < 2)
                   needed = 2;
   
           /* But we need to bound the transaction so we don't overflow the
            * journal. */
           if (needed > EXT3_MAX_TRANS_DATA) 
                   needed = EXT3_MAX_TRANS_DATA;
   
           return EXT3_DATA_TRANS_BLOCKS + needed;
   }
           
   /* 
    * Truncate transactions can be complex and absolutely huge.  So we need to
    * be able to restart the transaction at a conventient checkpoint to make
    * sure we don't overflow the journal.
    *
    * start_transaction gets us a new handle for a truncate transaction,
    * and extend_transaction tries to extend the existing one a bit.  If
    * extend fails, we need to propagate the failure up and restart the
    * transaction in the top-level truncate loop. --sct 
    */
   
   static handle_t *start_transaction(struct inode *inode) 
   {
           handle_t *result;
           
           result = ext3_journal_start(inode, blocks_for_truncate(inode));
           if (!IS_ERR(result))
                   return result;
           
           ext3_std_error(inode->i_sb, PTR_ERR(result));
           return result;
   }
   
   /*
    * Try to extend this transaction for the purposes of truncation.
    *
    * Returns 0 if we managed to create more room.  If we can't create more
    * room, and the transaction must be restarted we return 1.
    */
   static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
   {
           if (handle->h_buffer_credits > EXT3_RESERVE_TRANS_BLOCKS)
                   return 0;
           if (!ext3_journal_extend(handle, blocks_for_truncate(inode)))
                   return 0;
           return 1;
   }
   
   /*
    * Restart the transaction associated with *handle.  This does a commit,
    * so before we call here everything must be consistently dirtied against
    * this transaction.
    */
   static int ext3_journal_test_restart(handle_t *handle, struct inode *inode)
   {
           jbd_debug(2, "restarting handle %p\n", handle);
           return ext3_journal_restart(handle, blocks_for_truncate(inode));
   }
   
   /*
    * Called at each iput()
    */
   void ext3_put_inode (struct inode * inode)
   {
           ext3_discard_prealloc (inode);
   }
   
   /*
    * Called at the last iput() if i_nlink is zero.
    */
   void ext3_delete_inode (struct inode * inode)
   {
           handle_t *handle;
           
           if (is_bad_inode(inode) ||
               inode->i_ino == EXT3_ACL_IDX_INO ||
               inode->i_ino == EXT3_ACL_DATA_INO)
                   goto no_delete;
   
           lock_kernel();
           handle = start_transaction(inode);
           if (IS_ERR(handle)) {
                   /* If we're going to skip the normal cleanup, we still
                    * need to make sure that the in-core orphan linked list
                    * is properly cleaned up. */
                   ext3_orphan_del(NULL, inode);
   
                   ext3_std_error(inode->i_sb, PTR_ERR(handle));
                   unlock_kernel();
                   goto no_delete;
           }
           
           if (IS_SYNC(inode))
                   handle->h_sync = 1;
           inode->i_size = 0;
           if (inode->i_blocks)
                   ext3_truncate(inode);
           /*
            * Kill off the orphan record which ext3_truncate created.
            * AKPM: I think this can be inside the above `if'.
            * Note that ext3_orphan_del() has to be able to cope with the
            * deletion of a non-existent orphan - this is because we don't
            * know if ext3_truncate() actually created an orphan record.
            * (Well, we could do this if we need to, but heck - it works)
            */
           ext3_orphan_del(handle, inode);
           inode->u.ext3_i.i_dtime = CURRENT_TIME;
   
           /* 
            * One subtle ordering requirement: if anything has gone wrong
            * (transaction abort, IO errors, whatever), then we can still
            * do these next steps (the fs will already have been marked as
            * having errors), but we can't free the inode if the mark_dirty
            * fails.  
            */
           if (ext3_mark_inode_dirty(handle, inode))
                   /* If that failed, just do the required in-core inode clear. */
                   clear_inode(inode);
           else
                   ext3_free_inode(handle, inode);
           ext3_journal_stop(handle, inode);
           unlock_kernel();
           return;
   no_delete:
           clear_inode(inode);     /* We must guarantee clearing of inode... */
   }
   
   void ext3_discard_prealloc (struct inode * inode)
   {
   #ifdef EXT3_PREALLOCATE
           lock_kernel();
           /* Writer: ->i_prealloc* */
           if (inode->u.ext3_i.i_prealloc_count) {
                   unsigned short total = inode->u.ext3_i.i_prealloc_count;
                   unsigned long block = inode->u.ext3_i.i_prealloc_block;
                   inode->u.ext3_i.i_prealloc_count = 0;
                   inode->u.ext3_i.i_prealloc_block = 0;
                   /* Writer: end */
                   ext3_free_blocks (inode, block, total);
           }
           unlock_kernel();
   #endif
   }
   
   static int ext3_alloc_block (handle_t *handle,
                           struct inode * inode, unsigned long goal, int *err)
   {
   #ifdef EXT3FS_DEBUG
           static unsigned long alloc_hits = 0, alloc_attempts = 0;
   #endif
           unsigned long result;
   
   #ifdef EXT3_PREALLOCATE
           /* Writer: ->i_prealloc* */
           if (inode->u.ext3_i.i_prealloc_count &&
               (goal == inode->u.ext3_i.i_prealloc_block ||
                goal + 1 == inode->u.ext3_i.i_prealloc_block))
           {
                   result = inode->u.ext3_i.i_prealloc_block++;
                   inode->u.ext3_i.i_prealloc_count--;
                   /* Writer: end */
                   ext3_debug ("preallocation hit (%lu/%lu).\n",
                               ++alloc_hits, ++alloc_attempts);
           } else {
                   ext3_discard_prealloc (inode);
                   ext3_debug ("preallocation miss (%lu/%lu).\n",
                               alloc_hits, ++alloc_attempts);
                   if (S_ISREG(inode->i_mode))
                           result = ext3_new_block (inode, goal, 
                                    &inode->u.ext3_i.i_prealloc_count,
                                    &inode->u.ext3_i.i_prealloc_block, err);
                   else
                           result = ext3_new_block (inode, goal, 0, 0, err);
                   /*
                    * AKPM: this is somewhat sticky.  I'm not surprised it was
                    * disabled in 2.2's ext3.  Need to integrate b_committed_data
                    * guarding with preallocation, if indeed preallocation is
                    * effective.
                    */
           }
   #else
           result = ext3_new_block (handle, 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);
   }
   
   /**
    *      ext3_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
    *
    *      To store the locations of file's data ext3 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 ext3_block_to_path(struct inode *inode, long i_block, int offsets[4])
   {
           int ptrs = EXT3_ADDR_PER_BLOCK(inode->i_sb);
           int ptrs_bits = EXT3_ADDR_PER_BLOCK_BITS(inode->i_sb);
           const long direct_blocks = EXT3_NDIR_BLOCKS,
                   indirect_blocks = ptrs,
                   double_blocks = (1 << (ptrs_bits * 2));
           int n = 0;
   
           if (i_block < 0) {
                   ext3_warning (inode->i_sb, "ext3_block_to_path", "block < 0");
           } else if (i_block < direct_blocks) {
                   offsets[n++] = i_block;
           } else if ( (i_block -= direct_blocks) < indirect_blocks) {
                   offsets[n++] = EXT3_IND_BLOCK;
                   offsets[n++] = i_block;
           } else if ((i_block -= indirect_blocks) < double_blocks) {
                   offsets[n++] = EXT3_DIND_BLOCK;
                   offsets[n++] = i_block >> ptrs_bits;
                   offsets[n++] = i_block & (ptrs - 1);
           } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
                   offsets[n++] = EXT3_TIND_BLOCK;
                   offsets[n++] = i_block >> (ptrs_bits * 2);
                   offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
                   offsets[n++] = i_block & (ptrs - 1);
           } else {
                   ext3_warning (inode->i_sb, "ext3_block_to_path", "block > big");
           }
           return n;
   }
   
   /**
    *      ext3_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 *ext3_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, inode->u.ext3_i.i_data + *offsets);
           if (!p->key)
                   goto no_block;
           while (--depth) {
                   bh = sb_bread(sb, le32_to_cpu(p->key));
                   if (!bh)
                           goto failure;
                   /* Reader: pointers */
                   if (!verify_chain(chain, p))
                           goto changed;
                   add_chain(++p, bh, (u32*)bh->b_data + *++offsets);
                   /* Reader: end */
                   if (!p->key)
                           goto no_block;
           }
           return NULL;
   
   changed:
           brelse(bh);
           *err = -EAGAIN;
           goto no_block;
   failure:
           *err = -EIO;
   no_block:
           return p;
   }
   
   /**
    *      ext3_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. 
    *      Caller must make sure that @ind is valid and will stay that way.
    */
   
   static inline unsigned long ext3_find_near(struct inode *inode, Indirect *ind)
   {
           u32 *start = ind->bh ? (u32*) ind->bh->b_data : inode->u.ext3_i.i_data;
           u32 *p;
   
           /* 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.
            */
           return (inode->u.ext3_i.i_block_group * 
                   EXT3_BLOCKS_PER_GROUP(inode->i_sb)) +
                  le32_to_cpu(inode->i_sb->u.ext3_sb.s_es->s_first_data_block);
   }
   
   /**
    *      ext3_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 int ext3_find_goal(struct inode *inode, long block, Indirect chain[4],
                             Indirect *partial, unsigned long *goal)
   {
           /* Writer: ->i_next_alloc* */
           if (block == inode->u.ext3_i.i_next_alloc_block + 1) {
                   inode->u.ext3_i.i_next_alloc_block++;
                   inode->u.ext3_i.i_next_alloc_goal++;
           }
   #ifdef SEARCH_FROM_ZERO
           inode->u.ext3_i.i_next_alloc_block = 0;
           inode->u.ext3_i.i_next_alloc_goal = 0;
   #endif
           /* Writer: end */
           /* Reader: pointers, ->i_next_alloc* */
           if (verify_chain(chain, partial)) {
                   /*
                    * try the heuristic for sequential allocation,
                    * failing that at least try to get decent locality.
                    */
                   if (block == inode->u.ext3_i.i_next_alloc_block)
                           *goal = inode->u.ext3_i.i_next_alloc_goal;
                   if (!*goal)
                           *goal = ext3_find_near(inode, partial);
   #ifdef SEARCH_FROM_ZERO
                   *goal = 0;
   #endif
                   return 0;
           }
           /* Reader: end */
           return -EAGAIN;
   }
   
   /**
    *      ext3_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 ext3_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 ext3_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
    *      ext3_alloc_block() (normally -ENOSPC). Otherwise we set the chain
    *      as described above and return 0.
    */
   
   static int ext3_alloc_branch(handle_t *handle, struct inode *inode,
                                int num,
                                unsigned long goal,
                                int *offsets,
                                Indirect *branch)
   {
           int blocksize = inode->i_sb->s_blocksize;
           int n = 0, keys = 0;
           int err = 0;
           int i;
           int parent = ext3_alloc_block(handle, 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 = ext3_alloc_block(handle, inode, parent, &err);
                           if (!nr)
                                   break;
                           branch[n].key = cpu_to_le32(nr);
                           keys = n+1;
                           
                           /*
                            * 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);
                           branch[n].bh = bh;
                           lock_buffer(bh);
                           BUFFER_TRACE(bh, "call get_create_access");
                           err = ext3_journal_get_create_access(handle, bh);
                           if (err) {
                                   unlock_buffer(bh);
                                   brelse(bh);
                                   break;
                           }
   
                           memset(bh->b_data, 0, blocksize);
                           branch[n].p = (u32*) bh->b_data + offsets[n];
                           *branch[n].p = branch[n].key;
                           BUFFER_TRACE(bh, "marking uptodate");
                           mark_buffer_uptodate(bh, 1);
                           unlock_buffer(bh);
   
                           BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
                           err = ext3_journal_dirty_metadata(handle, bh);
                           if (err)
                                   break;
                           
                           parent = nr;
                   }
           }
           if (n == num)
                   return 0;
   
           /* Allocation failed, free what we already allocated */
           for (i = 1; i < keys; i++) {
                   BUFFER_TRACE(branch[i].bh, "call journal_forget");
                   ext3_journal_forget(handle, branch[i].bh);
           }
           for (i = 0; i < keys; i++)
                   ext3_free_blocks(handle, inode, le32_to_cpu(branch[i].key), 1);
           return err;
   }
   
   /**
    *      ext3_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
    *              ext3_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 int ext3_splice_branch(handle_t *handle, struct inode *inode, long block,
                                 Indirect chain[4], Indirect *where, int num)
   {
           int i;
           int err = 0;
   
           /*
            * If we're splicing into a [td]indirect block (as opposed to the
            * inode) then we need to get write access to the [td]indirect block
            * before the splice.
            */
           if (where->bh) {
                   BUFFER_TRACE(where->bh, "get_write_access");
                   err = ext3_journal_get_write_access(handle, where->bh);
                   if (err)
                           goto err_out;
           }
           /* Verify that place we are splicing to is still there and vacant */
   
           /* Writer: pointers, ->i_next_alloc* */
           if (!verify_chain(chain, where-1) || *where->p)
                   /* Writer: end */
                   goto changed;
   
           /* That's it */
   
           *where->p = where->key;
           inode->u.ext3_i.i_next_alloc_block = block;
           inode->u.ext3_i.i_next_alloc_goal = le32_to_cpu(where[num-1].key);
   #ifdef SEARCH_FROM_ZERO
           inode->u.ext3_i.i_next_alloc_block = 0;
           inode->u.ext3_i.i_next_alloc_goal = 0;
   #endif
           /* Writer: end */
   
           /* We are done with atomic stuff, now do the rest of housekeeping */
   
           inode->i_ctime = CURRENT_TIME;
           ext3_mark_inode_dirty(handle, inode);
   
           /* had we spliced it onto indirect block? */
           if (where->bh) {
                   /*
                    * akpm: If we spliced it onto an indirect block, we haven't
                    * altered the inode.  Note however that if it is being spliced
                    * onto an indirect block at the very end of the file (the
                    * file is growing) then we *will* alter the inode to reflect
                    * the new i_size.  But that is not done here - it is done in
                    * generic_commit_write->__mark_inode_dirty->ext3_dirty_inode.
                    */
                   jbd_debug(5, "splicing indirect only\n");
                   BUFFER_TRACE(where->bh, "call ext3_journal_dirty_metadata");
                   err = ext3_journal_dirty_metadata(handle, where->bh);
                   if (err) 
                           goto err_out;
           } else {
                   /*
                    * OK, we spliced it into the inode itself on a direct block.
                    * Inode was dirtied above.
                    */
                   jbd_debug(5, "splicing direct\n");
           }
           return err;
   
   changed:
           /*
            * AKPM: if where[i].bh isn't part of the current updating
            * transaction then we explode nastily.  Test this code path.
            */
           jbd_debug(1, "the chain changed: try again\n");
           err = -EAGAIN;
           
   err_out:
           for (i = 1; i < num; i++) {
                   BUFFER_TRACE(where[i].bh, "call journal_forget");
                   ext3_journal_forget(handle, where[i].bh);
           }
           /* For the normal collision cleanup case, we free up the blocks.
            * On genuine filesystem errors we don't even think about doing
            * that. */
           if (err == -EAGAIN)
                   for (i = 0; i < num; i++)
                           ext3_free_blocks(handle, inode, 
                                            le32_to_cpu(where[i].key), 1);
           return err;
   }
   
   /*
    * 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.
    *
    * akpm: `handle' can be NULL if create == 0.
    *
    * The BKL may not be held on entry here.  Be sure to take it early.
    */
   
   static int ext3_get_block_handle(handle_t *handle, struct inode *inode, 
                                    long 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 depth = ext3_block_to_path(inode, iblock, offsets);
           loff_t new_size;
   
           J_ASSERT(handle != NULL || create == 0);
   
           if (depth == 0)
                   goto out;
   
           lock_kernel();
   reread:
           partial = ext3_get_branch(inode, depth, offsets, chain, &err);
   
           /* Simplest case - block found, no allocation needed */
           if (!partial) {
                   bh_result->b_state &= ~(1UL << BH_New);
   got_it:
                   bh_result->b_dev = inode->i_dev;
                   bh_result->b_blocknr = le32_to_cpu(chain[depth-1].key);
                   bh_result->b_state |= (1UL << BH_Mapped);
                   /* 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) {
                           BUFFER_TRACE(partial->bh, "call brelse");
                           brelse(partial->bh);
                           partial--;
                   }
                   BUFFER_TRACE(bh_result, "returned");
                   unlock_kernel();
   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;
   
           if (ext3_find_goal(inode, iblock, chain, partial, &goal) < 0)
                   goto changed;
   
           left = (chain + depth) - partial;
   
           /*
            * Block out ext3_truncate while we alter the tree
            */
           down_read(&inode->u.ext3_i.truncate_sem);
           err = ext3_alloc_branch(handle, inode, left, goal,
                                           offsets+(partial-chain), partial);
   
           /* The ext3_splice_branch call will free and forget any buffers
            * on the new chain if there is a failure, but that risks using
            * up transaction credits, especially for bitmaps where the
            * credits cannot be returned.  Can we handle this somehow?  We
            * may need to return -EAGAIN upwards in the worst case.  --sct */
           if (!err)
                   err = ext3_splice_branch(handle, inode, iblock, chain,
                                            partial, left);
           up_read(&inode->u.ext3_i.truncate_sem);
           if (err == -EAGAIN)
                   goto changed;
           if (err)
                   goto cleanup;
   
           new_size = inode->i_size;
           /*
            * This is not racy against ext3_truncate's modification of i_disksize
            * because VM/VFS ensures that the file cannot be extended while
            * truncate is in progress.  It is racy between multiple parallel
            * instances of get_block, but we have the BKL.
            */
           if (new_size > inode->u.ext3_i.i_disksize)
                   inode->u.ext3_i.i_disksize = new_size;
   
           bh_result->b_state |= (1UL << BH_New);
           goto got_it;
   
   changed:
           while (partial > chain) {
                   jbd_debug(1, "buffer chain changed, retrying\n");
                   BUFFER_TRACE(partial->bh, "brelsing");
                   brelse(partial->bh);
                   partial--;
           }
           goto reread;
   }
   
   /*
    * The BKL is not held on entry here.
    */
   static int ext3_get_block(struct inode *inode, long iblock,
                           struct buffer_head *bh_result, int create)
   {
           handle_t *handle = 0;
           int ret;
   
           if (create) {
                   handle = ext3_journal_current_handle();
                   J_ASSERT(handle != 0);
           }
           ret = ext3_get_block_handle(handle, inode, iblock, bh_result, create);
           return ret;
   }
   
   /*
    * `handle' can be NULL if create is zero
    */
   struct buffer_head *ext3_getblk(handle_t *handle, struct inode * inode,
                                   long block, int create, int * errp)
   {
           struct buffer_head dummy;
           int fatal = 0, err;
           
           J_ASSERT(handle != NULL || create == 0);
   
           dummy.b_state = 0;
           dummy.b_blocknr = -1000;
           buffer_trace_init(&dummy.b_history);
           *errp = ext3_get_block_handle(handle, inode, block, &dummy, create);
           if (!*errp && buffer_mapped(&dummy)) {
                   struct buffer_head *bh;
                   bh = sb_getblk(inode->i_sb, dummy.b_blocknr);
                   if (buffer_new(&dummy)) {
                           J_ASSERT(create != 0);
                           J_ASSERT(handle != 0);
   
                           /* Now that we do not always journal data, we
                              should keep in mind whether this should
                              always journal the new buffer as metadata.
                              For now, regular file writes use
                              ext3_get_block instead, so it's not a
                              problem. */
                           lock_kernel();
                           lock_buffer(bh);
                           BUFFER_TRACE(bh, "call get_create_access");
                           fatal = ext3_journal_get_create_access(handle, bh);
                           if (!fatal) {
                                   memset(bh->b_data, 0,
                                          inode->i_sb->s_blocksize);
                                   mark_buffer_uptodate(bh, 1);
                           }
                           unlock_buffer(bh);
                           BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
                           err = ext3_journal_dirty_metadata(handle, bh);
                           if (!fatal) fatal = err;
                           unlock_kernel();
                   } else {
                           BUFFER_TRACE(bh, "not a new buffer");
                   }
                   if (fatal) {
                           *errp = fatal;
                           brelse(bh);
                           bh = NULL;
                   }
                   return bh;
           }
           return NULL;
   }
   
   struct buffer_head *ext3_bread(handle_t *handle, struct inode * inode,
                                  int block, int create, int *err)
   {
           struct buffer_head * bh;
           int prev_blocks;
   
           prev_blocks = inode->i_blocks;
   
           bh = ext3_getblk (handle, inode, block, create, err);
           if (!bh)
                   return bh;
   #ifdef EXT3_PREALLOCATE
           /*
            * If the inode has grown, and this is a directory, then use a few
            * more of the preallocated blocks to keep directory fragmentation
            * down.  The preallocated blocks are guaranteed to be contiguous.
            */
           if (create &&
               S_ISDIR(inode->i_mode) &&
               inode->i_blocks > prev_blocks &&
               EXT3_HAS_COMPAT_FEATURE(inode->i_sb,
                                       EXT3_FEATURE_COMPAT_DIR_PREALLOC)) {
                   int i;
                   struct buffer_head *tmp_bh;
   
                   for (i = 1;
                        inode->u.ext3_i.i_prealloc_count &&
                        i < EXT3_SB(inode->i_sb)->s_es->s_prealloc_dir_blocks;
                        i++) {
                           /*
                            * ext3_getblk will zero out the contents of the
                            * directory for us
                            */
                           tmp_bh = ext3_getblk(handle, inode,
                                                   block+i, create, err);
                           if (!tmp_bh) {
                                   brelse (bh);
                                   return 0;
                           }
                           brelse (tmp_bh);
                   }
           }
   #endif
           if (buffer_uptodate(bh))
                   return bh;
           ll_rw_block (READ, 1, &bh);
           wait_on_buffer (bh);
           if (buffer_uptodate(bh))
                   return bh;
           brelse (bh);
           *err = -EIO;
           return NULL;
   }
   
   static int walk_page_buffers(   handle_t *handle,
                                   struct inode *inode,
                                   struct buffer_head *head,
                                   unsigned from,
                                   unsigned to,
                                   int *partial,
                                   int (*fn)(      handle_t *handle,
                                                   struct inode *inode,
                                                   struct buffer_head *bh))
   {
           struct buffer_head *bh;
           unsigned block_start, block_end;
           unsigned blocksize = head->b_size;
           int err, ret = 0;
   
           for (   bh = head, block_start = 0;
                   ret == 0 && (bh != head || !block_start);
                   block_start = block_end, bh = bh->b_this_page)
           {
                   block_end = block_start + blocksize;
                   if (block_end <= from || block_start >= to) {
                           if (partial && !buffer_uptodate(bh))
                                   *partial = 1;
                           continue;
                   }
                   err = (*fn)(handle, inode, bh);
                   if (!ret)
                           ret = err;
           }
           return ret;
   }
   
   /*
    * To preserve ordering, it is essential that the hole instantiation and
   * the data write be encapsulated in a single transaction.  We cannot
   * close off a transaction and start a new one between the ext3_get_block()
   * and the commit_write().  So doing the journal_start at the start of
   * prepare_write() is the right place.
   *
   * Also, this function can nest inside ext3_writepage() ->
   * block_write_full_page(). In that case, we *know* that ext3_writepage()
   * has generated enough buffer credits to do the whole page.  So we won't
   * block on the journal in that case, which is good, because the caller may
   * be PF_MEMALLOC.
   *
   * By accident, ext3 can be reentered when a transaction is open via
   * quota file writes.  If we were to commit the transaction while thus
   * reentered, there can be a deadlock - we would be holding a quota
   * lock, and the commit would never complete if another thread had a
   * transaction open and was blocking on the quota lock - a ranking
   * violation.
   *
   * So what we do is to rely on the fact that journal_stop/journal_start
   * will _not_ run commit under these circumstances because handle->h_ref
   * is elevated.  We'll still have enough credits for the tiny quotafile
   * write.  
   */
  
  static int do_journal_get_write_access(handle_t *handle, struct inode *inode,
                                         struct buffer_head *bh)
  {
          return ext3_journal_get_write_access(handle, bh);
  }
  
  static int ext3_prepare_write(struct file *file, struct page *page,
                                unsigned from, unsigned to)
  {
          struct inode *inode = page->mapping->host;
          int ret, needed_blocks = ext3_writepage_trans_blocks(inode);
          handle_t *handle;
  
          lock_kernel();
          handle = ext3_journal_start(inode, needed_blocks);
          if (IS_ERR(handle)) {
                  ret = PTR_ERR(handle);
                  goto out;
          }
          unlock_kernel();
          ret = block_prepare_write(page, from, to, ext3_get_block);
          lock_kernel();
          if (ret != 0)
                  goto prepare_write_failed;
  
          if (ext3_should_journal_data(inode)) {
                  ret = walk_page_buffers(handle, inode, page->buffers,
                                  from, to, NULL, do_journal_get_write_access);
                  if (ret) {
                          /*
                           * We're going to fail this prepare_write(),
                           * so commit_write() will not be called.
                           * We need to undo block_prepare_write()'s kmap().
                           * AKPM: Do we need to clear PageUptodate?  I don't
                           * think so.
                           */
                          kunmap(page);
                  }
          }
  prepare_write_failed:
          if (ret)
                  ext3_journal_stop(handle, inode);
  out:
          unlock_kernel();
          return ret;
  }
  
  static int journal_dirty_sync_data(handle_t *handle, struct inode *inode,
                                     struct buffer_head *bh)
  {
          int ret = ext3_journal_dirty_data(handle, bh, 0);
          buffer_insert_inode_data_queue(bh, inode);
          return ret;
  }
  
  /*
   * For ext3_writepage().  We also brelse() the buffer to account for
   * the bget() which ext3_writepage() performs.
   */
  static int journal_dirty_async_data(handle_t *handle, struct inode *inode, 
                                      struct buffer_head *bh)
  {
          int ret = ext3_journal_dirty_data(handle, bh, 1);
          buffer_insert_inode_data_queue(bh, inode);
          __brelse(bh);
          return ret;
  }
  
  /* For commit_write() in data=journal mode */
  static int commit_write_fn(handle_t *handle, struct inode *inode, 
                             struct buffer_head *bh)
  {
          set_bit(BH_Uptodate, &bh->b_state);
          return ext3_journal_dirty_metadata(handle, bh);
  }
  
  /*
   * We need to pick up the new inode size which generic_commit_write gave us
   * `file' can be NULL - eg, when called from block_symlink().
   *
   * ext3 inode->i_dirty_buffers policy:  If we're journalling data we
   * definitely don't want them to appear on the inode at all - instead
   * we need to manage them at the JBD layer and we need to intercept
   * the relevant sync operations and translate them into journal operations.
   *
   * If we're not journalling data then we can just leave the buffers
   * on ->i_dirty_buffers.  If someone writes them out for us then thanks.
   * Otherwise we'll do it in commit, if we're using ordered data.
   */
  
  static int ext3_commit_write(struct file *file, struct page *page,
                               unsigned from, unsigned to)
  {
          handle_t *handle = ext3_journal_current_handle();
          struct inode *inode = page->mapping->host;
          int ret = 0, ret2;
  
          lock_kernel();
          if (ext3_should_journal_data(inode)) {
                  /*
                   * Here we duplicate the generic_commit_write() functionality
                   */
                  int partial = 0;
                  loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
  
                  ret = walk_page_buffers(handle, inode, page->buffers,
                          from, to, &partial, commit_write_fn);
                  if (!partial)
                          SetPageUptodate(page);
                  kunmap(page);
                  if (pos > inode->i_size)
                          inode->i_size = pos;
                  EXT3_I(inode)->i_state |= EXT3_STATE_JDATA;
          } else {
                  if (ext3_should_order_data(inode)) {
                          ret = walk_page_buffers(handle, inode, page->buffers,
                                  from, to, NULL, journal_dirty_sync_data);
                  }
                  /* Be careful here if generic_commit_write becomes a
                   * required invocation after block_prepare_write. */
                  if (ret == 0) {
                          ret = generic_commit_write(file, page, from, to);
                  } else {
                          /*
                           * block_prepare_write() was called, but we're not
                           * going to call generic_commit_write().  So we
                           * need to perform generic_commit_write()'s kunmap
                           * by hand.
                           */
                          kunmap(page);
                  }
          }
          if (inode->i_size > inode->u.ext3_i.i_disksize) {
                  inode->u.ext3_i.i_disksize = inode->i_size;
                  ret2 = ext3_mark_inode_dirty(handle, inode);
                  if (!ret) 
                          ret = ret2;
          }
          ret2 = ext3_journal_stop(handle, inode);
          unlock_kernel();
          if (!ret)
                  ret = ret2;
          return ret;
  }
  
  /* 
   * bmap() is special.  It gets used by applications such as lilo and by
   * the swapper to find the on-disk block of a specific piece of data.
   *
   * Naturally, this is dangerous if the block concerned is still in the
   * journal.  If somebody makes a swapfile on an ext3 data-journaling
   * filesystem and enables swap, then they may get a nasty shock when the
   * data getting swapped to that swapfile suddenly gets overwritten by
   * the original zero's written out previously to the journal and
   * awaiting writeback in the kernel's buffer cache. 
   *
   * So, if we see any bmap calls here on a modified, data-journaled file,
   * take extra steps to flush any blocks which might be in the cache. 
   */
  static int ext3_bmap(struct address_space *mapping, long block)
  {
          struct inode *inode = mapping->host;
          journal_t *journal;
          int err;
          
          if (EXT3_I(inode)->i_state & EXT3_STATE_JDATA) {
                  /* 
                   * This is a REALLY heavyweight approach, but the use of
                   * bmap on dirty files is expected to be extremely rare:
                   * only if we run lilo or swapon on a freshly made file
                   * do we expect this to happen. 
                   *
                   * (bmap requires CAP_SYS_RAWIO so this does not
                   * represent an unprivileged user DOS attack --- we'd be
                   * in trouble if mortal users could trigger this path at
                   * will.) 
                   *
                   * NB. EXT3_STATE_JDATA is not set on files other than
                   * regular files.  If somebody wants to bmap a directory
                   * or symlink and gets confused because the buffer
                   * hasn't yet been flushed to disk, they deserve
                   * everything they get.
                   */
                  
                  EXT3_I(inode)->i_state &= ~EXT3_STATE_JDATA;
                  journal = EXT3_JOURNAL(inode);
                  journal_lock_updates(journal);
                  err = journal_flush(journal);
                  journal_unlock_updates(journal);
                  
                  if (err)
                          return 0;
          }
          
          return generic_block_bmap(mapping,block,ext3_get_block);
  }
  
  static int bget_one(handle_t *handle, struct inode *inode, 
                      struct buffer_head *bh)
  {
          atomic_inc(&bh->b_count);
          return 0;
  }
  
  /*
   * Note that we always start a transaction even if we're not journalling
   * data.  This is to preserve ordering: any hole instantiation within
   * __block_write_full_page -> ext3_get_block() should be journalled
   * along with the data so we don't crash and then get metadata which
   * refers to old data.
   *
   * In all journalling modes block_write_full_page() will start the I/O.
   *
   * Problem:
   *
   *      ext3_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
   *              ext3_writepage()
   *
   * Similar for:
   *
   *      ext3_file_write() -> generic_file_write() -> __alloc_pages() -> ...
   *
   * Same applies to ext3_get_block().  We will deadlock on various things like
   * lock_journal and i_truncate_sem.
   *
   * Setting PF_MEMALLOC here doesn't work - too many internal memory
   * allocations fail.
   *
   * 16May01: If we're reentered then journal_current_handle() will be
   *          non-zero. We simply *return*.
   *
   * 1 July 2001: @@@ FIXME:
   *   In journalled data mode, a data buffer may be metadata against the
   *   current transaction.  But the same file is part of a shared mapping
   *   and someone does a writepage() on it.
   *
   *   We will move the buffer onto the async_data list, but *after* it has
   *   been dirtied. So there's a small window where we have dirty data on
   *   BJ_Metadata.
   *
   *   Note that this only applies to the last partial page in the file.  The
   *   bit which block_write_full_page() uses prepare/commit for.  (That's
   *   broken code anyway: it's wrong for msync()).
   *
   *   It's a rare case: affects the final partial page, for journalled data
   *   where the file is subject to bith write() and writepage() in the same
   *   transction.  To fix it we'll need a custom block_write_full_page().
   *   We'll probably need that anyway for journalling writepage() output.
   *
   * We don't honour synchronous mounts for writepage().  That would be
   * disastrous.  Any write() or metadata operation will sync the fs for
   * us.
   */
  static int ext3_writepage(struct page *page)
  {
          struct inode *inode = page->mapping->host;
          struct buffer_head *page_buffers;
          handle_t *handle = NULL;
          int ret = 0, err;
          int needed;
          int order_data;
  
          J_ASSERT(PageLocked(page));
          
          /*
           * We give up here if we're reentered, because it might be
           * for a different filesystem.  One *could* look for a
           * nested transaction opportunity.
           */
          lock_kernel();
          if (ext3_journal_current_handle())
                  goto out_fail;
  
          needed = ext3_writepage_trans_blocks(inode);
          if (current->flags & PF_MEMALLOC)
                  handle = ext3_journal_try_start(inode, needed);
          else
                  handle = ext3_journal_start(inode, needed);
                                  
          if (IS_ERR(handle)) {
                  ret = PTR_ERR(handle);
                  goto out_fail;
          }
  
          order_data = ext3_should_order_data(inode) ||
                          ext3_should_journal_data(inode);
  
          unlock_kernel();
  
          page_buffers = NULL;    /* Purely to prevent compiler warning */
  
          /* bget() all the buffers */
          if (order_data) {
                  if (!page->buffers)
                          create_empty_buffers(page,
                                  inode->i_dev, inode->i_sb->s_blocksize);
                  page_buffers = page->buffers;
                  walk_page_buffers(handle, inode, page_buffers, 0,
                                  PAGE_CACHE_SIZE, NULL, bget_one);
          }
  
          ret = block_write_full_page(page, ext3_get_block);
  
          /*
           * The page can become unlocked at any point now, and
           * truncate can then come in and change things.  So we
           * can't touch *page from now on.  But *page_buffers is
           * safe due to elevated refcount.
           */
  
          handle = ext3_journal_current_handle();
          lock_kernel();
  
          /* And attach them to the current transaction */
          if (order_data) {
                  err = walk_page_buffers(handle, inode, page_buffers,
                          0, PAGE_CACHE_SIZE, NULL, journal_dirty_async_data);
                  if (!ret)
                          ret = err;
          }
  
          err = ext3_journal_stop(handle, inode);
          if (!ret)
                  ret = err;
          unlock_kernel();
          return ret;
  
  out_fail:
          
          unlock_kernel();
          SetPageDirty(page);
          UnlockPage(page);
          return ret;
  }
  
  static int ext3_readpage(struct file *file, struct page *page)
  {
          return block_read_full_page(page,ext3_get_block);
  }
  
  
  static int ext3_flushpage(struct page *page, unsigned long offset)
  {
          journal_t *journal = EXT3_JOURNAL(page->mapping->host);
          return journal_flushpage(journal, page, offset);
  }
  
  static int ext3_releasepage(struct page *page, int wait)
  {
          journal_t *journal = EXT3_JOURNAL(page->mapping->host);
          return journal_try_to_free_buffers(journal, page, wait);
  }
  
  
  struct address_space_operations ext3_aops = {
          readpage:       ext3_readpage,          /* BKL not held.  Don't need */
          writepage:      ext3_writepage,         /* BKL not held.  We take it */
          sync_page:      block_sync_page,
          prepare_write:  ext3_prepare_write,     /* BKL not held.  We take it */
          commit_write:   ext3_commit_write,      /* BKL not held.  We take it */
          bmap:           ext3_bmap,              /* BKL held */
          flushpage:      ext3_flushpage,         /* BKL not held.  Don't need */
          releasepage:    ext3_releasepage,       /* BKL not held.  Don't need */
  };
  
  /*
   * ext3_block_truncate_page() zeroes out a mapping from file offset `from'
   * up to the end of the block which corresponds to `from'.
   * This required during truncate. We need to physically zero the tail end
   * of that block so it doesn't yield old data if the file is later grown.
   */
  static int ext3_block_truncate_page(handle_t *handle,
                  struct address_space *mapping, loff_t from)
  {
          unsigned long index = from >> PAGE_CACHE_SHIFT;
          unsigned offset = from & (PAGE_CACHE_SIZE-1);
          unsigned blocksize, iblock, length, pos;
          struct inode *inode = mapping->host;
          struct page *page;
          struct buffer_head *bh;
          int err;
  
          blocksize = inode->i_sb->s_blocksize;
          length = offset & (blocksize - 1);
  
          /* Block boundary? Nothing to do */
          if (!length)
                  return 0;
  
          length = blocksize - length;
          iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
  
          page = find_or_create_page(mapping, index, GFP_NOFS);
          err = -ENOMEM;
          if (!page)
                  goto out;
  
          if (!page->buffers)
                  create_empty_buffers(page, inode->i_dev, blocksize);
  
          /* Find the buffer that contains "offset" */
          bh = page->buffers;
          pos = blocksize;
          while (offset >= pos) {
                  bh = bh->b_this_page;
                  iblock++;
                  pos += blocksize;
          }
  
          err = 0;
          if (!buffer_mapped(bh)) {
                  /* Hole? Nothing to do */
                  if (buffer_uptodate(bh))
                          goto unlock;
                  ext3_get_block(inode, iblock, bh, 0);
                  /* Still unmapped? Nothing to do */
                  if (!buffer_mapped(bh))
                          goto unlock;
          }
  
          /* Ok, it's mapped. Make sure it's up-to-date */
          if (Page_Uptodate(page))
                  set_bit(BH_Uptodate, &bh->b_state);
  
          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;
          }
  
          if (ext3_should_journal_data(inode)) {
                  BUFFER_TRACE(bh, "get write access");
                  err = ext3_journal_get_write_access(handle, bh);
                  if (err)
                          goto unlock;
          }
          
          memset(kmap(page) + offset, 0, length);
          flush_dcache_page(page);
          kunmap(page);
  
          BUFFER_TRACE(bh, "zeroed end of block");
  
          err = 0;
          if (ext3_should_journal_data(inode)) {
                  err = ext3_journal_dirty_metadata(handle, bh);
          } else {
                  if (ext3_should_order_data(inode))
                          err = ext3_journal_dirty_data(handle, bh, 0);
                  __mark_buffer_dirty(bh);
          }
  
  unlock:
          UnlockPage(page);
          page_cache_release(page);
  out:
          return err;
  }
  
  /*
   * 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;
  }
  
  /**
   *      ext3_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 ext3_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 ext3_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 ext3_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].
   *                      (no partially truncated stuff there).  */
  
  static Indirect *ext3_find_shared(struct inode *inode,
                                  int depth,
                                  int offsets[4],
                                  Indirect chain[4],
                                  u32 *top)
  {
          Indirect *partial, *p;
          int k, err;
  
          *top = 0;
          /* Make k index the deepest non-null offest + 1 */
          for (k = depth; k > 1 && !offsets[k-1]; k--)
                  ;
          partial = ext3_get_branch(inode, k, offsets, chain, &err);
          /* Writer: pointers */
          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.
           */
          if (!partial->key && *partial->p)
                  /* Writer: end */
                  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;
                  /* Nope, don't do this in ext3.  Must leave the tree intact */
  #if 0
                  *p->p = 0;
  #endif
          }
          /* Writer: end */
  
          while(partial > p)
          {
                  brelse(partial->bh);
                  partial--;
          }
  no_top:
          return partial;
  }
  
  /*
   * Zero a number of block pointers in either an inode or an indirect block.
   * If we restart the transaction we must again get write access to the
   * indirect block for further modification.
   *
   * We release `count' blocks on disk, but (last - first) may be greater
   * than `count' because there can be holes in there.
   */
  static void
  ext3_clear_blocks(handle_t *handle, struct inode *inode, struct buffer_head *bh,
                  unsigned long block_to_free, unsigned long count,
                  u32 *first, u32 *last)
  {
          u32 *p;
          if (try_to_extend_transaction(handle, inode)) {
                  if (bh) {
                          BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
                          ext3_journal_dirty_metadata(handle, bh);
                  }
                  ext3_mark_inode_dirty(handle, inode);
                  ext3_journal_test_restart(handle, inode);
                  if (bh) {
                          BUFFER_TRACE(bh, "retaking write access");
                          ext3_journal_get_write_access(handle, bh);
                  }
          }
  
          /*
           * Any buffers which are on the journal will be in memory. We find
           * them on the hash table so journal_revoke() will run journal_forget()
           * on them.  We've already detached each block from the file, so
           * bforget() in journal_forget() should be safe.
           *
           * AKPM: turn on bforget in journal_forget()!!!
           */
          for (p = first; p < last; p++) {
                  u32 nr = le32_to_cpu(*p);
                  if (nr) {
                          struct buffer_head *bh;
  
                          *p = 0;
                          bh = sb_get_hash_table(inode->i_sb, nr);
                          ext3_forget(handle, 0, inode, bh, nr);
                  }
          }
  
          ext3_free_blocks(handle, inode, block_to_free, count);
  }
  
  /**
   * ext3_free_data - free a list of data blocks
   * @handle:     handle for this transaction
   * @inode:      inode we are dealing with
   * @this_bh:    indirect buffer_head which contains *@first and *@last
   * @first:      array of block numbers
   * @last:       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.
   *
   * We accumulate contiguous runs of blocks to free.  Conveniently, if these
   * blocks are contiguous then releasing them at one time will only affect one
   * or two bitmap blocks (+ group descriptor(s) and superblock) and we won't
   * actually use a lot of journal space.
   *
   * @this_bh will be %NULL if @first and @last point into the inode's direct
   * block pointers.
   */
  static void ext3_free_data(handle_t *handle, struct inode *inode,
                             struct buffer_head *this_bh, u32 *first, u32 *last)
  {
          unsigned long block_to_free = 0;    /* Starting block # of a run */
          unsigned long count = 0;            /* Number of blocks in the run */ 
          u32 *block_to_free_p = NULL;        /* Pointer into inode/ind
                                                 corresponding to
                                                 block_to_free */
          unsigned long nr;                   /* Current block # */
          u32 *p;                             /* Pointer into inode/ind
                                                 for current block */
          int err;
  
          if (this_bh) {                          /* For indirect block */
                  BUFFER_TRACE(this_bh, "get_write_access");
                  err = ext3_journal_get_write_access(handle, this_bh);
                  /* Important: if we can't update the indirect pointers
                   * to the blocks, we can't free them. */
                  if (err)
                          return;
          }
  
          for (p = first; p < last; p++) {
                  nr = le32_to_cpu(*p);
                  if (nr) {
                          /* accumulate blocks to free if they're contiguous */
                          if (count == 0) {
                                  block_to_free = nr;
                                  block_to_free_p = p;
                                  count = 1;
                          } else if (nr == block_to_free + count) {
                                  count++;
                          } else {
                                  ext3_clear_blocks(handle, inode, this_bh, 
                                                    block_to_free,
                                                    count, block_to_free_p, p);
                                  block_to_free = nr;
                                  block_to_free_p = p;
                                  count = 1;
                          }
                  }
          }
  
          if (count > 0)
                  ext3_clear_blocks(handle, inode, this_bh, block_to_free,
                                    count, block_to_free_p, p);
  
          if (this_bh) {
                  BUFFER_TRACE(this_bh, "call ext3_journal_dirty_metadata");
                  ext3_journal_dirty_metadata(handle, this_bh);
          }
  }
  
  /**
   *      ext3_free_branches - free an array of branches
   *      @handle: JBD handle for this transaction
   *      @inode: inode we are dealing with
   *      @parent_bh: the buffer_head which contains *@first and *@last
   *      @first: array of block numbers
   *      @last:  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 ext3_free_branches(handle_t *handle, struct inode *inode,
                                 struct buffer_head *parent_bh,
                                 u32 *first, u32 *last, int depth)
  {
          unsigned long nr;
          u32 *p;
  
          if (is_handle_aborted(handle))
                  return;
          
          if (depth--) {
                  struct buffer_head *bh;
                  int addr_per_block = EXT3_ADDR_PER_BLOCK(inode->i_sb);
                  p = last;
                  while (--p >= first) {
                          nr = le32_to_cpu(*p);
                          if (!nr)
                                  continue;               /* A hole */
  
                          /* Go read the buffer for the next level down */
                          bh = sb_bread(inode->i_sb, nr);
  
                          /*
                           * A read failure? Report error and clear slot
                           * (should be rare).
                           */
                          if (!bh) {
                                  ext3_error(inode->i_sb, "ext3_free_branches",
                                             "Read failure, inode=%ld, block=%ld",
                                             inode->i_ino, nr);
                                  continue;
                          }
  
                          /* This zaps the entire block.  Bottom up. */
                          BUFFER_TRACE(bh, "free child branches");
                          ext3_free_branches(handle, inode, bh, (u32*)bh->b_data,
                                             (u32*)bh->b_data + addr_per_block,
                                             depth);
  
                          /*
                           * We've probably journalled the indirect block several
                           * times during the truncate.  But it's no longer
                           * needed and we now drop it from the transaction via
                           * journal_revoke().
                           *
                           * That's easy if it's exclusively part of this
                           * transaction.  But if it's part of the committing
                           * transaction then journal_forget() will simply
                           * brelse() it.  That means that if the underlying
                           * block is reallocated in ext3_get_block(),
                           * unmap_underlying_metadata() will find this block
                           * and will try to get rid of it.  damn, damn.
                           *
                           * If this block has already been committed to the
                           * journal, a revoke record will be written.  And
                           * revoke records must be emitted *before* clearing
                           * this block's bit in the bitmaps.
                           */
                          ext3_forget(handle, 1, inode, bh, bh->b_blocknr);
  
                          /*
                           * Everything below this this pointer has been
                           * released.  Now let this top-of-subtree go.
                           *
                           * We want the freeing of this indirect block to be
                           * atomic in the journal with the updating of the
                           * bitmap block which owns it.  So make some room in
                           * the journal.
                           *
                           * We zero the parent pointer *after* freeing its
                           * pointee in the bitmaps, so if extend_transaction()
                           * for some reason fails to put the bitmap changes and
                           * the release into the same transaction, recovery
                           * will merely complain about releasing a free block,
                           * rather than leaking blocks.
                           */
                          if (is_handle_aborted(handle))
                                  return;
                          if (try_to_extend_transaction(handle, inode)) {
                                  ext3_mark_inode_dirty(handle, inode);
                                  ext3_journal_test_restart(handle, inode);
                          }
  
                          ext3_free_blocks(handle, inode, nr, 1);
  
                          if (parent_bh) {
                                  /*
                                   * The block which we have just freed is
                                   * pointed to by an indirect block: journal it
                                   */
                                  BUFFER_TRACE(parent_bh, "get_write_access");
                                  if (!ext3_journal_get_write_access(handle,
                                                                     parent_bh)){
                                          *p = 0;
                                          BUFFER_TRACE(parent_bh,
                                          "call ext3_journal_dirty_metadata");
                                          ext3_journal_dirty_metadata(handle, 
                                                                      parent_bh);
                                  }
                          }
                  }
          } else {
                  /* We have reached the bottom of the tree. */
                  BUFFER_TRACE(parent_bh, "free data blocks");
                  ext3_free_data(handle, inode, parent_bh, first, last);
          }
  }
  
  /*
   * ext3_truncate()
   *
   * We block out ext3_get_block() block instantiations across the entire
   * transaction, and VFS/VM ensures that ext3_truncate() cannot run
   * simultaneously on behalf of the same inode.
   *
   * As we work through the truncate and commmit bits of it to the journal there
   * is one core, guiding principle: the file's tree must always be consistent on
   * disk.  We must be able to restart the truncate after a crash.
   *
   * The file's tree may be transiently inconsistent in memory (although it
   * probably isn't), but whenever we close off and commit a journal transaction,
   * the contents of (the filesystem + the journal) must be consistent and
   * restartable.  It's pretty simple, really: bottom up, right to left (although
   * left-to-right works OK too).
   *
   * Note that at recovery time, journal replay occurs *before* the restart of
   * truncate against the orphan inode list.
   *
   * The committed inode has the new, desired i_size (which is the same as
   * i_disksize in this case).  After a crash, ext3_orphan_cleanup() will see
   * that this inode's truncate did not complete and it will again call
   * ext3_truncate() to have another go.  So there will be instantiated blocks
   * to the right of the truncation point in a crashed ext3 filesystem.  But
   * that's fine - as long as they are linked from the inode, the post-crash
   * ext3_truncate() run will find them and release them.
   */
  
  void ext3_truncate(struct inode * inode)
  {
          handle_t *handle;
          u32 *i_data = inode->u.ext3_i.i_data;
          int addr_per_block = EXT3_ADDR_PER_BLOCK(inode->i_sb);
          int offsets[4];
          Indirect chain[4];
          Indirect *partial;
          int nr = 0;
          int n;
          long last_block;
          unsigned blocksize;
  
          if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
              S_ISLNK(inode->i_mode)))
                  return;
          if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
                  return;
  
          ext3_discard_prealloc(inode);
  
          handle = start_transaction(inode);
          if (IS_ERR(handle))
                  return;         /* AKPM: return what? */
  
          blocksize = inode->i_sb->s_blocksize;
          last_block = (inode->i_size + blocksize-1)
                                          >> EXT3_BLOCK_SIZE_BITS(inode->i_sb);
  
          ext3_block_truncate_page(handle, inode->i_mapping, inode->i_size);
                  
  
          n = ext3_block_to_path(inode, last_block, offsets);
          if (n == 0)
                  goto out_stop;  /* error */
  
          /*
           * OK.  This truncate is going to happen.  We add the inode to the
           * orphan list, so that if this truncate spans multiple transactions,
           * and we crash, we will resume the truncate when the filesystem
           * recovers.  It also marks the inode dirty, to catch the new size.
           *
           * Implication: the file must always be in a sane, consistent
           * truncatable state while each transaction commits.
           */
          if (ext3_orphan_add(handle, inode))
                  goto out_stop;
  
          /*
           * The orphan list entry will now protect us from any crash which
           * occurs before the truncate completes, so it is now safe to propagate
           * the new, shorter inode size (held for now in i_size) into the
           * on-disk inode. We do this via i_disksize, which is the value which
           * ext3 *really* writes onto the disk inode.
           */
          inode->u.ext3_i.i_disksize = inode->i_size;
  
          /*
           * From here we block out all ext3_get_block() callers who want to
           * modify the block allocation tree.
           */
          down_write(&inode->u.ext3_i.truncate_sem);
  
          if (n == 1) {           /* direct blocks */
                  ext3_free_data(handle, inode, NULL, i_data+offsets[0],
                                 i_data + EXT3_NDIR_BLOCKS);
                  goto do_indirects;
          }
  
          partial = ext3_find_shared(inode, n, offsets, chain, &nr);
          /* Kill the top of shared branch (not detached) */
          if (nr) {
                  if (partial == chain) {
                          /* Shared branch grows from the inode */
                          ext3_free_branches(handle, inode, NULL,
                                             &nr, &nr+1, (chain+n-1) - partial);
                          *partial->p = 0;
                          /*
                           * We mark the inode dirty prior to restart,
                           * and prior to stop.  No need for it here.
                           */
                  } else {
                          /* Shared branch grows from an indirect block */
                          BUFFER_TRACE(partial->bh, "get_write_access");
                          ext3_free_branches(handle, inode, partial->bh,
                                          partial->p,
                                          partial->p+1, (chain+n-1) - partial);
                  }
          }
          /* Clear the ends of indirect blocks on the shared branch */
          while (partial > chain) {
                  ext3_free_branches(handle, inode, partial->bh, partial->p + 1,
                                     (u32*)partial->bh->b_data + addr_per_block,
                                     (chain+n-1) - partial);
                  BUFFER_TRACE(partial->bh, "call brelse");
                  brelse (partial->bh);
                  partial--;
          }
  do_indirects:
          /* Kill the remaining (whole) subtrees */
          switch (offsets[0]) {
                  default:
                          nr = i_data[EXT3_IND_BLOCK];
                          if (nr) {
                                  ext3_free_branches(handle, inode, NULL,
                                                     &nr, &nr+1, 1);
                                  i_data[EXT3_IND_BLOCK] = 0;
                          }
                  case EXT3_IND_BLOCK:
                          nr = i_data[EXT3_DIND_BLOCK];
                          if (nr) {
                                  ext3_free_branches(handle, inode, NULL,
                                                     &nr, &nr+1, 2);
                                  i_data[EXT3_DIND_BLOCK] = 0;
                          }
                  case EXT3_DIND_BLOCK:
                          nr = i_data[EXT3_TIND_BLOCK];
                          if (nr) {
                                  ext3_free_branches(handle, inode, NULL,
                                                     &nr, &nr+1, 3);
                                  i_data[EXT3_TIND_BLOCK] = 0;
                          }
                  case EXT3_TIND_BLOCK:
                          ;
          }
          up_write(&inode->u.ext3_i.truncate_sem);
          inode->i_mtime = inode->i_ctime = CURRENT_TIME;
          ext3_mark_inode_dirty(handle, inode);
  
          /* In a multi-transaction truncate, we only make the final
           * transaction synchronous */
          if (IS_SYNC(inode))
                  handle->h_sync = 1;
  out_stop:
          /*
           * If this was a simple ftruncate(), and the file will remain alive
           * then we need to clear up the orphan record which we created above.
           * However, if this was a real unlink then we were called by
           * ext3_delete_inode(), and we allow that function to clean up the
           * orphan info for us.
           */
          if (inode->i_nlink)
                  ext3_orphan_del(handle, inode);
  
          ext3_journal_stop(handle, inode);
  }
  
  /* 
   * ext3_get_inode_loc returns with an extra refcount against the
   * inode's underlying buffer_head on success. 
   */
  
  int ext3_get_inode_loc (struct inode *inode, struct ext3_iloc *iloc)
  {
          struct buffer_head *bh = 0;
          unsigned long block;
          unsigned long block_group;
          unsigned long group_desc;
          unsigned long desc;
          unsigned long offset;
          struct ext3_group_desc * gdp;
                  
          if ((inode->i_ino != EXT3_ROOT_INO &&
                  inode->i_ino != EXT3_ACL_IDX_INO &&
                  inode->i_ino != EXT3_ACL_DATA_INO &&
                  inode->i_ino != EXT3_JOURNAL_INO &&
                  inode->i_ino < EXT3_FIRST_INO(inode->i_sb)) ||
                  inode->i_ino > le32_to_cpu(
                          inode->i_sb->u.ext3_sb.s_es->s_inodes_count)) {
                  ext3_error (inode->i_sb, "ext3_get_inode_loc",
                              "bad inode number: %lu", inode->i_ino);
                  goto bad_inode;
          }
          block_group = (inode->i_ino - 1) / EXT3_INODES_PER_GROUP(inode->i_sb);
          if (block_group >= inode->i_sb->u.ext3_sb.s_groups_count) {
                  ext3_error (inode->i_sb, "ext3_get_inode_loc",
                              "group >= groups count");
                  goto bad_inode;
          }
          group_desc = block_group >> EXT3_DESC_PER_BLOCK_BITS(inode->i_sb);
          desc = block_group & (EXT3_DESC_PER_BLOCK(inode->i_sb) - 1);
          bh = inode->i_sb->u.ext3_sb.s_group_desc[group_desc];
          if (!bh) {
                  ext3_error (inode->i_sb, "ext3_get_inode_loc",
                              "Descriptor not loaded");
                  goto bad_inode;
          }
  
          gdp = (struct ext3_group_desc *) bh->b_data;
          /*
           * Figure out the offset within the block group inode table
           */
          offset = ((inode->i_ino - 1) % EXT3_INODES_PER_GROUP(inode->i_sb)) *
                  EXT3_INODE_SIZE(inode->i_sb);
          block = le32_to_cpu(gdp[desc].bg_inode_table) +
                  (offset >> EXT3_BLOCK_SIZE_BITS(inode->i_sb));
          if (!(bh = sb_bread(inode->i_sb, block))) {
                  ext3_error (inode->i_sb, "ext3_get_inode_loc",
                              "unable to read inode block - "
                              "inode=%lu, block=%lu", inode->i_ino, block);
                  goto bad_inode;
          }
          offset &= (EXT3_BLOCK_SIZE(inode->i_sb) - 1);
  
          iloc->bh = bh;
          iloc->raw_inode = (struct ext3_inode *) (bh->b_data + offset);
          iloc->block_group = block_group;
          
          return 0;
          
   bad_inode:
          return -EIO;
  }
  
  void ext3_set_inode_flags(struct inode *inode)
  {
          unsigned int flags = inode->u.ext3_i.i_flags;
  
          inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME);
          if (flags & EXT3_SYNC_FL)
                  inode->i_flags |= S_SYNC;
          if (flags & EXT3_APPEND_FL)
                  inode->i_flags |= S_APPEND;
          if (flags & EXT3_IMMUTABLE_FL)
                  inode->i_flags |= S_IMMUTABLE;
          if (flags & EXT3_NOATIME_FL)
                  inode->i_flags |= S_NOATIME;
  }
  
  
  void ext3_read_inode(struct inode * inode)
  {
          struct ext3_iloc iloc;
          struct ext3_inode *raw_inode;
          struct buffer_head *bh;
          int block;
          
          if(ext3_get_inode_loc(inode, &iloc))
                  goto bad_inode;
          bh = iloc.bh;
          raw_inode = iloc.raw_inode;
          init_rwsem(&inode->u.ext3_i.truncate_sem);
          inode->i_mode = le16_to_cpu(raw_inode->i_mode);
          inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
          inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
          if(!(test_opt (inode->i_sb, NO_UID32))) {
                  inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
                  inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
          }
          inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
          inode->i_size = le32_to_cpu(raw_inode->i_size);
          inode->i_atime = le32_to_cpu(raw_inode->i_atime);
          inode->i_ctime = le32_to_cpu(raw_inode->i_ctime);
          inode->i_mtime = le32_to_cpu(raw_inode->i_mtime);
          inode->u.ext3_i.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) {
                  if (inode->i_mode == 0 ||
                      !(inode->i_sb->u.ext3_sb.s_mount_state & EXT3_ORPHAN_FS)) {
                          /* this inode is deleted */
                          brelse (bh);
                          goto bad_inode;
                  }
                  /* The only unlinked inodes we let through here have
                   * valid i_mode and are being read by the orphan
                   * recovery code: that's fine, we're about to complete
                   * the process of deleting those. */
          }
          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);
          inode->i_version = ++event;
          inode->u.ext3_i.i_flags = le32_to_cpu(raw_inode->i_flags);
  #ifdef EXT3_FRAGMENTS
          inode->u.ext3_i.i_faddr = le32_to_cpu(raw_inode->i_faddr);
          inode->u.ext3_i.i_frag_no = raw_inode->i_frag;
          inode->u.ext3_i.i_frag_size = raw_inode->i_fsize;
  #endif
          inode->u.ext3_i.i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
          if (!S_ISREG(inode->i_mode)) {
                  inode->u.ext3_i.i_dir_acl = le32_to_cpu(raw_inode->i_dir_acl);
          } else {
                  inode->i_size |=
                          ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
          }
          inode->u.ext3_i.i_disksize = inode->i_size;
          inode->i_generation = le32_to_cpu(raw_inode->i_generation);
  #ifdef EXT3_PREALLOCATE
          inode->u.ext3_i.i_prealloc_count = 0;
  #endif
          inode->u.ext3_i.i_block_group = iloc.block_group;
  
          /*
           * 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 (block = 0; block < EXT3_N_BLOCKS; block++)
                  inode->u.ext3_i.i_data[block] = iloc.raw_inode->i_block[block];
          INIT_LIST_HEAD(&inode->u.ext3_i.i_orphan);
  
          if (inode->i_ino == EXT3_ACL_IDX_INO ||
              inode->i_ino == EXT3_ACL_DATA_INO)
                  /* Nothing to do */ ;
          else if (S_ISREG(inode->i_mode)) {
                  inode->i_op = &ext3_file_inode_operations;
                  inode->i_fop = &ext3_file_operations;
                  inode->i_mapping->a_ops = &ext3_aops;
          } else if (S_ISDIR(inode->i_mode)) {
                  inode->i_op = &ext3_dir_inode_operations;
                  inode->i_fop = &ext3_dir_operations;
          } else if (S_ISLNK(inode->i_mode)) {
                  if (!inode->i_blocks)
                          inode->i_op = &ext3_fast_symlink_inode_operations;
                  else {
                          inode->i_op = &page_symlink_inode_operations;
                          inode->i_mapping->a_ops = &ext3_aops;
                  }
          } else 
                  init_special_inode(inode, inode->i_mode,
                                     le32_to_cpu(iloc.raw_inode->i_block[0]));
          brelse(iloc.bh);
          ext3_set_inode_flags(inode);
          return;
          
  bad_inode:
          make_bad_inode(inode);
          return;
  }
  
  /*
   * Post the struct inode info into an on-disk inode location in the
   * buffer-cache.  This gobbles the caller's reference to the
   * buffer_head in the inode location struct.  
   */
  
  static int ext3_do_update_inode(handle_t *handle, 
                                  struct inode *inode, 
                                  struct ext3_iloc *iloc)
  {
          struct ext3_inode *raw_inode = iloc->raw_inode;
          struct buffer_head *bh = iloc->bh;
          int err = 0, rc, block;
  
          if (handle) {
                  BUFFER_TRACE(bh, "get_write_access");
                  err = ext3_journal_get_write_access(handle, bh);
                  if (err)
                          goto out_brelse;
          }
          raw_inode->i_mode = cpu_to_le16(inode->i_mode);
          if(!(test_opt(inode->i_sb, NO_UID32))) {
                  raw_inode->i_uid_low = cpu_to_le16(low_16_bits(inode->i_uid));
                  raw_inode->i_gid_low = cpu_to_le16(low_16_bits(inode->i_gid));
  /*
   * Fix up interoperability with old kernels. Otherwise, old inodes get
   * re-used with the upper 16 bits of the uid/gid intact
   */
                  if(!inode->u.ext3_i.i_dtime) {
                          raw_inode->i_uid_high =
                                  cpu_to_le16(high_16_bits(inode->i_uid));
                          raw_inode->i_gid_high =
                                  cpu_to_le16(high_16_bits(inode->i_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(inode->i_uid));
                  raw_inode->i_gid_low =
                          cpu_to_le16(fs_high2lowgid(inode->i_gid));
                  raw_inode->i_uid_high = 0;
                  raw_inode->i_gid_high = 0;
          }
          raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
          raw_inode->i_size = cpu_to_le32(inode->u.ext3_i.i_disksize);
          raw_inode->i_atime = cpu_to_le32(inode->i_atime);
          raw_inode->i_ctime = cpu_to_le32(inode->i_ctime);
          raw_inode->i_mtime = cpu_to_le32(inode->i_mtime);
          raw_inode->i_blocks = cpu_to_le32(inode->i_blocks);
          raw_inode->i_dtime = cpu_to_le32(inode->u.ext3_i.i_dtime);
          raw_inode->i_flags = cpu_to_le32(inode->u.ext3_i.i_flags);
  #ifdef EXT3_FRAGMENTS
          raw_inode->i_faddr = cpu_to_le32(inode->u.ext3_i.i_faddr);
          raw_inode->i_frag = inode->u.ext3_i.i_frag_no;
          raw_inode->i_fsize = inode->u.ext3_i.i_frag_size;
  #else
          /* If we are not tracking these fields in the in-memory inode,
           * then preserve them on disk, but still initialise them to zero
           * for new inodes. */
          if (EXT3_I(inode)->i_state & EXT3_STATE_NEW) {
                  raw_inode->i_faddr = 0;
                  raw_inode->i_frag = 0;
                  raw_inode->i_fsize = 0;
          }
  #endif
          raw_inode->i_file_acl = cpu_to_le32(inode->u.ext3_i.i_file_acl);
          if (!S_ISREG(inode->i_mode)) {
                  raw_inode->i_dir_acl = cpu_to_le32(inode->u.ext3_i.i_dir_acl);
          } else {
                  raw_inode->i_size_high =
                          cpu_to_le32(inode->u.ext3_i.i_disksize >> 32);
                  if (inode->u.ext3_i.i_disksize > 0x7fffffffULL) {
                          struct super_block *sb = inode->i_sb;
                          if (!EXT3_HAS_RO_COMPAT_FEATURE(sb,
                                          EXT3_FEATURE_RO_COMPAT_LARGE_FILE) ||
                              EXT3_SB(sb)->s_es->s_rev_level ==
                                          cpu_to_le32(EXT3_GOOD_OLD_REV)) {
                                 /* If this is the first large file
                                  * created, add a flag to the superblock.
                                  */
                                  err = ext3_journal_get_write_access(handle,
                                                  sb->u.ext3_sb.s_sbh);
                                  if (err)
                                          goto out_brelse;
                                  ext3_update_dynamic_rev(sb);
                                  EXT3_SET_RO_COMPAT_FEATURE(sb,
                                          EXT3_FEATURE_RO_COMPAT_LARGE_FILE);
                                  sb->s_dirt = 1;
                                  handle->h_sync = 1;
                                  err = ext3_journal_dirty_metadata(handle,
                                                  sb->u.ext3_sb.s_sbh);
                          }
                  }
          }
          raw_inode->i_generation = cpu_to_le32(inode->i_generation);
          if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode))
                  raw_inode->i_block[0] =
                          cpu_to_le32(kdev_t_to_nr(inode->i_rdev));
          else for (block = 0; block < EXT3_N_BLOCKS; block++)
                  raw_inode->i_block[block] = inode->u.ext3_i.i_data[block];
  
          BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
          rc = ext3_journal_dirty_metadata(handle, bh);
          if (!err)
                  err = rc;
          EXT3_I(inode)->i_state &= ~EXT3_STATE_NEW;
  
  out_brelse:
          brelse (bh);
          ext3_std_error(inode->i_sb, err);
          return err;
  }
  
  /*
   * ext3_write_inode()
   *
   * We are called from a few places:
   *
   * - Within generic_file_write() for O_SYNC files.
   *   Here, there will be no transaction running. We wait for any running
   *   trasnaction to commit.
   *
   * - Within sys_sync(), kupdate and such.
   *   We wait on commit, if tol to.
   *
   * - Within prune_icache() (PF_MEMALLOC == true)
   *   Here we simply return.  We can't afford to block kswapd on the
   *   journal commit.
   *
   * In all cases it is actually safe for us to return without doing anything,
   * because the inode has been copied into a raw inode buffer in
   * ext3_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
   * knfsd.
   *
   * Note that we are absolutely dependent upon all inode dirtiers doing the
   * right thing: they *must* call mark_inode_dirty() after dirtying info in
   * which we are interested.
   *
   * It would be a bug for them to not do this.  The code:
   *
   *      mark_inode_dirty(inode)
   *      stuff();
   *      inode->i_size = expr;
   *
   * is in error because a kswapd-driven write_inode() could occur while
   * `stuff()' is running, and the new i_size will be lost.  Plus the inode
   * will no longer be on the superblock's dirty inode list.
   */
  void ext3_write_inode(struct inode *inode, int wait)
  {
          if (current->flags & PF_MEMALLOC)
                  return;
  
          if (ext3_journal_current_handle()) {
                  jbd_debug(0, "called recursively, non-PF_MEMALLOC!\n");
                  return;
          }
  
          if (!wait)
                  return;
  
          ext3_force_commit(inode->i_sb); 
  }
  
  /*
   * ext3_setattr()
   *
   * Called from notify_change.
   *
   * We want to trap VFS attempts to truncate the file as soon as
   * possible.  In particular, we want to make sure that when the VFS
   * shrinks i_size, we put the inode on the orphan list and modify
   * i_disksize immediately, so that during the subsequent flushing of
   * dirty pages and freeing of disk blocks, we can guarantee that any
   * commit will leave the blocks being flushed in an unused state on
   * disk.  (On recovery, the inode will get truncated and the blocks will
   * be freed, so we have a strong guarantee that no future commit will
   * leave these blocks visible to the user.)  
   *
   * This is only needed for regular files.  rmdir() has its own path, and
   * we can never truncate a direcory except on final unlink (at which
   * point i_nlink is zero so recovery is easy.)
   *
   * Called with the BKL.  
   */
  
  int ext3_setattr(struct dentry *dentry, struct iattr *attr)
  {
          struct inode *inode = dentry->d_inode;
          int error, rc = 0;
          const unsigned int ia_valid = attr->ia_valid;
  
          error = inode_change_ok(inode, attr);
          if (error)
                  return error;
  
          if ((ia_valid & ATTR_UID && attr->ia_uid != inode->i_uid) ||
                  (ia_valid & ATTR_GID && attr->ia_gid != inode->i_gid)) {
                  error = DQUOT_TRANSFER(inode, attr) ? -EDQUOT : 0;
                  if (error)
                          return error;
          }
  
          if (attr->ia_valid & ATTR_SIZE && attr->ia_size < inode->i_size) {
                  handle_t *handle;
  
                  handle = ext3_journal_start(inode, 3);
                  if (IS_ERR(handle)) {
                          error = PTR_ERR(handle);
                          goto err_out;
                  }
                  
                  error = ext3_orphan_add(handle, inode);
                  inode->u.ext3_i.i_disksize = attr->ia_size;
                  rc = ext3_mark_inode_dirty(handle, inode);
                  if (!error)
                          error = rc;
                  ext3_journal_stop(handle, inode);
          }
          
          rc = inode_setattr(inode, attr);
  
          /* If inode_setattr's call to ext3_truncate failed to get a
           * transaction handle at all, we need to clean up the in-core
           * orphan list manually. */
          if (inode->i_nlink)
                  ext3_orphan_del(NULL, inode);
  
  err_out:
          ext3_std_error(inode->i_sb, error);
          if (!error)
                  error = rc;
          return error;
  }
  
  
  /*
   * akpm: how many blocks doth make a writepage()?
   *
   * With N blocks per page, it may be:
   * N data blocks
   * 2 indirect block
   * 2 dindirect
   * 1 tindirect
   * N+5 bitmap blocks (from the above)
   * N+5 group descriptor summary blocks
   * 1 inode block
   * 1 superblock.
   * 2 * EXT3_SINGLEDATA_TRANS_BLOCKS for the quote files
   *
   * 3 * (N + 5) + 2 + 2 * EXT3_SINGLEDATA_TRANS_BLOCKS
   *
   * With ordered or writeback data it's the same, less the N data blocks.
   *
   * If the inode's direct blocks can hold an integral number of pages then a
   * page cannot straddle two indirect blocks, and we can only touch one indirect
   * and dindirect block, and the "5" above becomes "3".
   *
   * This still overestimates under most circumstances.  If we were to pass the
   * start and end offsets in here as well we could do block_to_path() on each
   * block and work out the exact number of indirects which are touched.  Pah.
   */
  
  int ext3_writepage_trans_blocks(struct inode *inode)
  {
          int bpp = ext3_journal_blocks_per_page(inode);
          int indirects = (EXT3_NDIR_BLOCKS % bpp) ? 5 : 3;
          int ret;
          
          if (ext3_should_journal_data(inode))
                  ret = 3 * (bpp + indirects) + 2;
          else
                  ret = 2 * (bpp + indirects) + 2;
  
  #ifdef CONFIG_QUOTA
          ret += 2 * EXT3_SINGLEDATA_TRANS_BLOCKS;
  #endif
  
          return ret;
  }
  
  int
  ext3_mark_iloc_dirty(handle_t *handle, 
                       struct inode *inode,
                       struct ext3_iloc *iloc)
  {
          int err = 0;
  
          if (handle) {
                  /* the do_update_inode consumes one bh->b_count */
                  atomic_inc(&iloc->bh->b_count);
                  err = ext3_do_update_inode(handle, inode, iloc);
                  /* ext3_do_update_inode() does journal_dirty_metadata */
                  brelse(iloc->bh);
          } else {
                  printk(KERN_EMERG "%s: called with no handle!\n", __FUNCTION__);
          }
          return err;
  }
  
  /* 
   * On success, We end up with an outstanding reference count against
   * iloc->bh.  This _must_ be cleaned up later. 
   */
  
  int
  ext3_reserve_inode_write(handle_t *handle, struct inode *inode, 
                           struct ext3_iloc *iloc)
  {
          int err = 0;
          if (handle) {
                  err = ext3_get_inode_loc(inode, iloc);
                  if (!err) {
                          BUFFER_TRACE(iloc->bh, "get_write_access");
                          err = ext3_journal_get_write_access(handle, iloc->bh);
                          if (err) {
                                  brelse(iloc->bh);
                                  iloc->bh = NULL;
                          }
                  }
          }
          ext3_std_error(inode->i_sb, err);
          return err;
  }
  
  /*
   * akpm: What we do here is to mark the in-core inode as clean
   * with respect to inode dirtiness (it may still be data-dirty).
   * This means that the in-core inode may be reaped by prune_icache
   * without having to perform any I/O.  This is a very good thing,
   * because *any* task may call prune_icache - even ones which
   * have a transaction open against a different journal.
   *
   * Is this cheating?  Not really.  Sure, we haven't written the
   * inode out, but prune_icache isn't a user-visible syncing function.
   * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
   * we start and wait on commits.
   *
   * Is this efficient/effective?  Well, we're being nice to the system
   * by cleaning up our inodes proactively so they can be reaped
   * without I/O.  But we are potentially leaving up to five seconds'
   * worth of inodes floating about which prune_icache wants us to
   * write out.  One way to fix that would be to get prune_icache()
   * to do a write_super() to free up some memory.  It has the desired
   * effect.
   */
  int ext3_mark_inode_dirty(handle_t *handle, struct inode *inode)
  {
          struct ext3_iloc iloc;
          int err;
  
          err = ext3_reserve_inode_write(handle, inode, &iloc);
          if (!err)
                  err = ext3_mark_iloc_dirty(handle, inode, &iloc);
          return err;
  }
  
  /*
   * akpm: ext3_dirty_inode() is called from __mark_inode_dirty()
   *
   * We're really interested in the case where a file is being extended.
   * i_size has been changed by generic_commit_write() and we thus need
   * to include the updated inode in the current transaction.
   *
   * Also, DQUOT_ALLOC_SPACE() will always dirty the inode when blocks
   * are allocated to the file.
   *
   * If the inode is marked synchronous, we don't honour that here - doing
   * so would cause a commit on atime updates, which we don't bother doing.
   * We handle synchronous inodes at the highest possible level.
   */
  void ext3_dirty_inode(struct inode *inode)
  {
          handle_t *current_handle = ext3_journal_current_handle();
          handle_t *handle;
  
          lock_kernel();
          handle = ext3_journal_start(inode, 2);
          if (IS_ERR(handle))
                  goto out;
          if (current_handle &&
                  current_handle->h_transaction != handle->h_transaction) {
                  /* This task has a transaction open against a different fs */
                  printk(KERN_EMERG "%s: transactions do not match!\n",
                          __FUNCTION__);
          } else {
                  jbd_debug(5, "marking dirty.  outer handle=%p\n",
                                  current_handle);
                  ext3_mark_inode_dirty(handle, inode);
          }
          ext3_journal_stop(handle, inode);
  out:
          unlock_kernel();
  }
  
  #ifdef AKPM
  /* 
   * Bind an inode's backing buffer_head into this transaction, to prevent
   * it from being flushed to disk early.  Unlike
   * ext3_reserve_inode_write, this leaves behind no bh reference and
   * returns no iloc structure, so the caller needs to repeat the iloc
   * lookup to mark the inode dirty later.
   */
  static inline int
  ext3_pin_inode(handle_t *handle, struct inode *inode)
  {
          struct ext3_iloc iloc;
          
          int err = 0;
          if (handle) {
                  err = ext3_get_inode_loc(inode, &iloc);
                  if (!err) {
                          BUFFER_TRACE(iloc.bh, "get_write_access");
                          err = journal_get_write_access(handle, iloc.bh);
                          if (!err)
                                  err = ext3_journal_dirty_metadata(handle, 
                                                                    iloc.bh);
                          brelse(iloc.bh);
                  }
          }
          ext3_std_error(inode->i_sb, err);
          return err;
  }
  #endif
  
  int ext3_change_inode_journal_flag(struct inode *inode, int val)
  {
          journal_t *journal;
          handle_t *handle;
          int err;
  
          /*
           * We have to be very careful here: changing a data block's
           * journaling status dynamically is dangerous.  If we write a
           * data block to the journal, change the status and then delete
           * that block, we risk forgetting to revoke the old log record
           * from the journal and so a subsequent replay can corrupt data.
           * So, first we make sure that the journal is empty and that
           * nobody is changing anything.
           */
  
          journal = EXT3_JOURNAL(inode);
          if (is_journal_aborted(journal) || IS_RDONLY(inode))
                  return -EROFS;
          
          journal_lock_updates(journal);
          journal_flush(journal);
  
          /*
           * OK, there are no updates running now, and all cached data is
           * synced to disk.  We are now in a completely consistent state
           * which doesn't have anything in the journal, and we know that
           * no filesystem updates are running, so it is safe to modify
           * the inode's in-core data-journaling state flag now.
           */
  
          if (val)
                  inode->u.ext3_i.i_flags |= EXT3_JOURNAL_DATA_FL;
          else
                  inode->u.ext3_i.i_flags &= ~EXT3_JOURNAL_DATA_FL;
  
          journal_unlock_updates(journal);
  
          /* Finally we can mark the inode as dirty. */
  
          handle = ext3_journal_start(inode, 1);
          if (IS_ERR(handle))
                  return PTR_ERR(handle);
  
          err = ext3_mark_inode_dirty(handle, inode);
          handle->h_sync = 1;
          ext3_journal_stop(handle, inode);
          ext3_std_error(inode->i_sb, err);
          
          return err;
  }
  
  
  /*
   * ext3_aops_journal_start().
   *
   * <This function died, but the comment lives on>
   *
   * We need to take the inode semaphore *outside* the
   * journal_start/journal_stop.  Otherwise, a different task could do a
   * wait_for_commit() while holding ->i_sem, which deadlocks.  The rule
   * is: transaction open/closes are considered to be a locking operation
   * and they nest *inside* ->i_sem.
   * ----------------------------------------------------------------------------
   * Possible problem:
   *      ext3_file_write()
   *      -> generic_file_write()
   *         -> __alloc_pages()
   *            -> page_launder()
   *               -> ext3_writepage()
   *
   * And the writepage can be on a different fs while we have a
   * transaction open against this one!  Bad.
   *
   * I tried making the task PF_MEMALLOC here, but that simply results in
   * 0-order allocation failures passed back to generic_file_write().
   * Instead, we rely on the reentrancy protection in ext3_writepage().
   * ----------------------------------------------------------------------------
   * When we do the journal_start() here we don't really need to reserve
   * any blocks - we won't need any until we hit ext3_prepare_write(),
   * which does all the needed journal extending.  However!  There is a
   * problem with quotas:
   *
   * Thread 1:
   * sys_sync
   * ->sync_dquots
   *   ->commit_dquot
   *     ->lock_dquot
   *     ->write_dquot
   *       ->ext3_file_write
   *         ->journal_start
   *         ->ext3_prepare_write
   *           ->journal_extend
   *           ->journal_start
   * Thread 2:
   * ext3_create          (for example)
   * ->ext3_new_inode
   *   ->dquot_initialize
   *     ->lock_dquot
   *
   * Deadlock.  Thread 1's journal_start blocks because thread 2 has a
   * transaction open.  Thread 2's transaction will never close because
   * thread 2 is stuck waiting for the dquot lock.
   *
   * So.  We must ensure that thread 1 *never* needs to extend the journal
   * for quota writes.  We do that by reserving enough journal blocks
   * here, in ext3_aops_journal_start() to ensure that the forthcoming "see if we
   * need to extend" test in ext3_prepare_write() succeeds.  
   */

Cache object: 71c686a12cfdb7990dfa2dced730ceee