From 07d09774e2bfa21dedcee3ef45892bb20827b12c Mon Sep 17 00:00:00 2001 From: Andrey Albershteyn Date: Wed, 20 May 2026 14:37:02 +0200 Subject: fsverity: generate and store zero-block hash 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 Acked-by: Eric Biggers Signed-off-by: Andrey Albershteyn Link: https://patch.msgid.link/20260520123722.405752-5-aalbersh@kernel.org Signed-off-by: Christian Brauner (Amutable) --- include/linux/fsverity.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include/linux') diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h index a8f9aa75b792..6c467ded9751 100644 --- a/include/linux/fsverity.h +++ b/include/linux/fsverity.h @@ -201,6 +201,8 @@ bool fsverity_verify_blocks(struct fsverity_info *vi, struct folio *folio, size_t len, size_t offset); void fsverity_verify_bio(struct fsverity_info *vi, struct bio *bio); void fsverity_enqueue_verify_work(struct work_struct *work); +void fsverity_fill_zerohash(struct folio *folio, size_t offset, size_t len, + struct fsverity_info *vi); #else /* !CONFIG_FS_VERITY */ @@ -281,6 +283,12 @@ static inline void fsverity_enqueue_verify_work(struct work_struct *work) WARN_ON_ONCE(1); } +static inline void fsverity_fill_zerohash(struct folio *folio, size_t offset, + size_t len, struct fsverity_info *vi) +{ + WARN_ON_ONCE(1); +} + #endif /* !CONFIG_FS_VERITY */ static inline bool fsverity_verify_folio(struct fsverity_info *vi, -- cgit v1.2.3