From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 70A943630A9; Thu, 19 Mar 2026 17:02:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773939768; cv=none; b=cmvDmivI5ObSajaB7Sn+A8I9UvmCAHshR2UXy5fN0fLtbrJft7yya8mQcwnmTdDdndB6QgpoA9dWBrk3K8jVjbxlSaZ/XG9bMvwD4E9aMu+pTyUNnjjKTKLsLlxCs7ZTbLJBZNtZ7rEWhMKB/X4ViQwv58dEQZaPk9yOuLtLDbo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773939768; c=relaxed/simple; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SoVrw1DFWl8U8qSjSmbainakKHupik72nSxZ9d4Lluhhex3okerH55GswrBd76ZCm6qHUyQ/9+OpyMSr0iNfGZEl19v4bDAi4bN5rfcXpdnN+cDPAFHNb3+o318RvJ4t4DDuTl2c00gkjdmWLuJR4lLSgiQp6r2eJrLGSwKNrQs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iu62A25X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iu62A25X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CBEA8C2BCAF; Thu, 19 Mar 2026 17:02:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773939768; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iu62A25XmdgGDJwUm3pyv7XhtJSzMaYt3ZE/zOnD4ewJhbp1jpwQlhTVQmckexfEx bgwV+bmU9har0cROHRgHod18toS7Gq/hZCzuPck1xjKdPt4DYvLAUx42g4DbvffEQg 4N6b+EvVdIBdG+xrYebiteWCjayTLcaV2P57KwS3xqXx0pzYuGHXP3lfm18VSa42Dg 3MA241YVB3HK5KvEYsOIP+jv+hGRYcDNEw3oSVdq0IcixgCppIJOX+NqraXQAPxBzS 5kioHeXvChxNLAiLUjaL6UuG1IOZdblCBp2BrcmyMHMWk9EkcXzd4pNSRrEH9NZD++ IjhkNjYVg7wIw== From: Andrey Albershteyn To: linux-xfs@vger.kernel.org, fsverity@lists.linux.dev, linux-fsdevel@vger.kernel.org, ebiggers@kernel.org Cc: Andrey Albershteyn , hch@lst.de, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-btrfs@vger.kernel.org, djwong@kernel.org Subject: [PATCH v5 03/25] fsverity: generate and store zero-block hash Date: Thu, 19 Mar 2026 18:01:50 +0100 Message-ID: <20260319170231.1455553-4-aalbersh@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260319170231.1455553-1-aalbersh@kernel.org> References: <20260319170231.1455553-1-aalbersh@kernel.org> Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 six data blocks and whose merkle tree looks roughly like this: root +--leaf0 | +--data0 | +--data1 | `--data2 `--leaf1 +--data3 +--data4 `--data5 If data[0-2] 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. Signed-off-by: Darrick J. Wong Signed-off-by: Andrey Albershteyn --- fs/verity/fsverity_private.h | 3 +++ fs/verity/open.c | 3 +++ 2 files changed, 6 insertions(+) diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index 6e6854c19078..35636c1e2c41 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -53,6 +53,9 @@ struct merkle_tree_params { u64 tree_size; /* Merkle tree size in bytes */ unsigned long tree_pages; /* Merkle tree size in pages */ + /* the hash of a merkle block-sized buffer of zeroes */ + u8 zero_digest[FS_VERITY_MAX_DIGEST_SIZE]; + /* * Starting block index for each tree level, ordered from leaf level (0) * to root level ('num_levels - 1') diff --git a/fs/verity/open.c b/fs/verity/open.c index 0483db672526..94407a37aa08 100644 --- a/fs/verity/open.c +++ b/fs/verity/open.c @@ -153,6 +153,9 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, goto out_err; } + fsverity_hash_block(params, page_address(ZERO_PAGE(0)), + params->zero_digest); + params->tree_size = offset << log_blocksize; params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT; return 0; -- 2.51.2