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ext4: disable merging of uninitialized extents

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Derived from Jan's patch:http://permalink.gmane.org/gmane.comp.file-systems.ext4/36470

Merging of uninitialized extents creates all sorts of interesting race
possibilities when writeback / DIO races with fallocate. Thus
ext4_convert_unwritten_extents_endio() has to deal with a case where
extent to be converted needs to be split out first. That isn't nice
for two reasons:

1) It may need allocation of extent tree block so ENOSPC is possible.
2) It complicates end_io handling code

So we disable merging of uninitialized extents which allows us to simplify
the code. Extents will get merged after they are converted to initialized
ones.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Dmitry Monakhov 2013-03-04 00:36:06 -05:00 committed by Theodore Ts'o
parent 357b66fdc8
commit ec22ba8edb
1 changed files with 5 additions and 3 deletions
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8
fs/ext4/extents.c
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@ -1584,10 +1584,12 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
unsigned short ext1_ee_len, ext2_ee_len, max_len;
/*
* Make sure that either both extents are uninitialized, or
* both are _not_.
* Make sure that both extents are initialized. We don't merge
* uninitialized extents so that we can be sure that end_io code has
* the extent that was written properly split out and conversion to
* initialized is trivial.
*/
if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2))
if (ext4_ext_is_uninitialized(ex1) || ext4_ext_is_uninitialized(ex2))
return 0;
if (ext4_ext_is_uninitialized(ex1))