On 2009-11-04, at 11:42, Leonard Michlmayr wrote:
Fiemap (ioctl) does not return any extents for small files on ext4.
(fm_start=0, fm_length=filesize)
File affected: fs/ext4/extents.c
I found the reason of the bug: wrong rounding. It will not only affect
small files, but any request that overlaps an extent boundary by less
that blocksize.
@@ -3700,7 +3701,8 @@
start_blk = start >> inode->i_sb->s_blocksize_bits;
- len_blks = len >> inode->i_sb->s_blocksize_bits;
+ end_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
+ len_blks = end_blk - start_blk + 1;
I don't think this is quite correct either. For example, if blocksize
is 1024
and start is 1023 (start_blk = 0) and len is 2 (end = 1024, end_blk =
1) then
len_blks = 2 which is too much.
I think the right calculation here is:
end_blk = (start + len + inode->i_sb->s_blocksize -
1) >>
inode->i_sb->s_blocksize_bits;
len_blks = end_blk - start_blk;
I'm also wondering (unrelated to this bug) why inode->i_sb-
>s_blocksize_bits
is used instead of inode->i_blkbits? That is probably worth a
separate cleanup
patch.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
