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ext4: return hole from ext4_map_blocks()

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Currently, ext4_map_blocks() just returns 0 when it finds a hole and
allocation is not requested. However we have all the information
available to tell how large the hole actually is and there are callers
of ext4_map_blocks() which would save some block-by-block hole iteration
if they knew this information. So fill in struct ext4_map_blocks even
for holes with the information we have. We keep returning 0 for holes to
maintain backward compatibility of the function.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2016-03-09 22:54:00 -05:00 committed by Theodore Ts'o
parent 140a52508a
commit facab4d971
3 changed files with 36 additions and 9 deletions
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11
fs/ext4/extents.c
View file

@ -4374,13 +4374,20 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
ext4_lblk_t hole_start, hole_len;
hole_start = map->m_lblk;
hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
/*
* put just found gap into cache to speed up
* subsequent requests
*/
hole_start = map->m_lblk;
hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
ext4_ext_put_gap_in_cache(inode, hole_start, hole_len);
/* Update hole_len to reflect hole size after map->m_lblk */
if (hole_start != map->m_lblk)
hole_len -= map->m_lblk - hole_start;
map->m_pblk = 0;
map->m_len = min_t(unsigned int, map->m_len, hole_len);
goto out2;
}

19
fs/ext4/indirect.c
View file

@ -555,8 +555,23 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
goto got_it;
}
/* Next simple case - plain lookup or failed read of indirect block */
if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
/* Next simple case - plain lookup failed */
if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
unsigned epb = inode->i_sb->s_blocksize / sizeof(u32);
int i;
/* Count number blocks in a subtree under 'partial' */
count = 1;
for (i = 0; partial + i != chain + depth - 1; i++)
count *= epb;
/* Fill in size of a hole we found */
map->m_pblk = 0;
map->m_len = min_t(unsigned int, map->m_len, count);
goto cleanup;
}
/* Failed read of indirect block */
if (err == -EIO)
goto cleanup;
/*

15
fs/ext4/inode.c
View file

@ -455,13 +455,13 @@ static void ext4_map_blocks_es_recheck(handle_t *handle,
* Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
* based files
*
* On success, it returns the number of blocks being mapped or allocated.
* if create==0 and the blocks are pre-allocated and unwritten block,
* the result buffer head is unmapped. If the create ==1, it will make sure
* the buffer head is mapped.
* On success, it returns the number of blocks being mapped or allocated. if
* create==0 and the blocks are pre-allocated and unwritten, the resulting @map
* is marked as unwritten. If the create == 1, it will mark @map as mapped.
*
* It returns 0 if plain look up failed (blocks have not been allocated), in
* that case, buffer head is unmapped
* that case, @map is returned as unmapped but we still do fill map->m_len to
* indicate the length of a hole starting at map->m_lblk.
*
* It returns the error in case of allocation failure.
*/
@ -504,6 +504,11 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
retval = map->m_len;
map->m_len = retval;
} else if (ext4_es_is_delayed(&es) || ext4_es_is_hole(&es)) {
map->m_pblk = 0;
retval = es.es_len - (map->m_lblk - es.es_lblk);
if (retval > map->m_len)
retval = map->m_len;
map->m_len = retval;
retval = 0;
} else {
BUG_ON(1);