Compute the hash of one filesystem block's worth of zeros. A filesystem
implementation can decide to elide merkle tree blocks containing only
this hash and synthesize the contents at read time.
Let's pretend that there's a file containing 131 data block and whose
merkle tree looks roughly like this:
root
+--leaf0
| +--data0
| +--data1
| +--...
| `--data128
`--leaf1
+--data129
+--data130
`--data131
If data[0-128] are sparse holes, then leaf0 will contain a repeating
sequence of @zero_digest. Therefore, leaf0 need not be written to disk
because its contents can be synthesized.
A subsequent xfs patch will use this to reduce the size of the merkle
tree when dealing with sparse gold master disk images and the like.
Note that this works only on the first-level (data holes). fsverity
doesn't store/generate zero_digest for any higher levels.
Add a helper to pre-fill folio with hashes of empty blocks. This will be
used by iomap to synthesize blocks full of zero hashes on the fly.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Acked-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Link: https://patch.msgid.link/20260520123722.405752-5-aalbersh@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Currently all reads of the fsverity hashes are kicked off from the data
I/O completion handler, leading to needlessly dependent I/O. This is
worked around a bit by performing readahead on the level 0 nodes, but
still fairly ineffective.
Switch to a model where the ->read_folio and ->readahead methods instead
kick off explicit readahead of the fsverity hashed so they are usually
available at I/O completion time.
For 64k sequential reads on my test VM this improves read performance
from 2.4GB/s - 2.6GB/s to 3.5GB/s - 3.9GB/s. The improvements for
random reads are likely to be even bigger.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Sterba <dsterba@suse.com> # btrfs
Link: https://lore.kernel.org/r/20260202060754.270269-5-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Require the invalidate_lock to be held over calls to
page_cache_ra_unbounded instead of acquiring it in this function.
This prepares for calling page_cache_ra_unbounded from ->readahead for
fsverity read-ahead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20260202060754.270269-3-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Issuing more reads on errors is not a good idea, especially when the
most common error here is -ENOMEM.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20260202060754.270269-2-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
ext4 and f2fs are largely using the same code to read a page full
of Merkle tree blocks from the page cache, and the upcoming xfs
fsverity support would add another copy.
Move the ext4 code to fs/verity/ and use it in f2fs as well. For f2fs
this removes the previous f2fs-specific error injection, but otherwise
the behavior remains unchanged.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andrey Albershteyn <aalbersh@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Link: https://lore.kernel.org/r/20260128152630.627409-7-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
