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ext4: allow ZERO_RANGE on encrypted files

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When ext4 encryption support was first added, ZERO_RANGE was disallowed,
supposedly because test failures (e.g. ext4/001) were seen when enabling
it, and at the time there wasn't enough time/interest to debug it.

However, there's actually no reason why ZERO_RANGE can't work on
encrypted files.  And it fact it *does* work now.  Whole blocks in the
zeroed range are converted to unwritten extents, as usual; encryption
makes no difference for that part.  Partial blocks are zeroed in the
pagecache and then ->writepages() encrypts those blocks as usual.
ext4_block_zero_page_range() handles reading and decrypting the block if
needed before actually doing the pagecache write.

Also, f2fs has always supported ZERO_RANGE on encrypted files.

As far as I can tell, the reason that ext4/001 was failing in v4.1 was
actually because of one of the bugs fixed by commit 36086d43f6 ("ext4
crypto: fix bugs in ext4_encrypted_zeroout()").  The bug made
ext4_encrypted_zeroout() always return a positive value, which caused
unwritten extents in encrypted files to sometimes not be marked as
initialized after being written to.  This bug was not actually in
ZERO_RANGE; it just happened to trigger during the extents manipulation
done in ext4/001 (and probably other tests too).

So, let's enable ZERO_RANGE on encrypted files on ext4.

Tested with:
	gce-xfstests -c ext4/encrypt -g auto
	gce-xfstests -c ext4/encrypt_1k -g auto

Got the same set of test failures both with and without this patch.
But with this patch 6 fewer tests are skipped: ext4/001, generic/008,
generic/009, generic/033, generic/096, and generic/511.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20191226154216.4808-1-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Eric Biggers 2019-12-26 09:42:16 -06:00 committed by Theodore Ts'o
parent 834f1565fa
commit 457b1e353c
2 changed files with 4 additions and 9 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
Documentation/filesystems/fscrypt.rst
View file

@ -975,9 +975,9 @@ astute users may notice some differences in behavior:
- Direct I/O is not supported on encrypted files. Attempts to use
direct I/O on such files will fall back to buffered I/O.
- The fallocate operations FALLOC_FL_COLLAPSE_RANGE,
FALLOC_FL_INSERT_RANGE, and FALLOC_FL_ZERO_RANGE are not supported
on encrypted files and will fail with EOPNOTSUPP.
- The fallocate operations FALLOC_FL_COLLAPSE_RANGE and
FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will
fail with EOPNOTSUPP.
- Online defragmentation of encrypted files is not supported. The
EXT4_IOC_MOVE_EXT and F2FS_IOC_MOVE_RANGE ioctls will fail with

7
fs/ext4/extents.c
View file

@ -4891,14 +4891,9 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
* range since we would need to re-encrypt blocks with a
* different IV or XTS tweak (which are based on the logical
* block number).
*
* XXX It's not clear why zero range isn't working, but we'll
* leave it disabled for encrypted inodes for now. This is a
* bug we should fix....
*/
if (IS_ENCRYPTED(inode) &&
(mode & (FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_INSERT_RANGE |
FALLOC_FL_ZERO_RANGE)))
(mode & (FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_INSERT_RANGE)))
return -EOPNOTSUPP;
/* Return error if mode is not supported */