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 F419B3EDAC1; Mon, 9 Mar 2026 19:24:27 +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=1773084268; cv=none; b=bDHF0e3ve5WMNW/1OMbVPzbCIZwzwR58vr/lx3jY+Lq0IlNFwZq8MOZdC9EujYBm4SanGVJCDo6tnH+JptOJNwEI/jBWwAEQPYD7aodRCczT6wdqQsmlqofzGU3bxtSa7w/+diCW2ivtAcP4zJWFF1PkTEwdKofgA2QfozdMOEQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773084268; c=relaxed/simple; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Ye/0S/H4Y2g4Mo7gzYlrY2/Fyk1uF1qJdpk5jyBclL7UKybjdwu/oaFkp0m5n6xUQbIQquz7ZFxQ5q+w6t5RPHl3TqPtfZEa5a/gGYFDHgNrIp5NZionJieS5KzgQWbwY7TyrxkHLrRCHssRIu1NusedTh8J+A1nVRpQBpGWpow= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Grn19QkK; 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="Grn19QkK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3ED76C2BCB0; Mon, 9 Mar 2026 19:24:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773084267; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Grn19QkKj5XpSF3fVfFe9jhpynhhJbkH1HpjjsPMvNtLiRgaHBWl7hYjbE8y+UKHa Gpxb8xC3TMlgOCWiYVCuZ1srjv2xRWkDQ7yodZPEumxG+Qj+wnSBxlM1zwoQhlLaWO F6Da5wljSesnhgjWj0io2Sl1Te96tnH+a5Tx9/snzo1DO0YWICtuFp5nO6M/lKJWpa cc6YTLg8NVTQ5ML50KHeDOEJatNiMWizF8B9qqKCb7t//TwL+ypU5A2wRJ/zYob3A+ KUbdgxrFrBEEwDyF41ZyGJM5pdGjM357a4JlszzJbrj/86JPKDKQJYHJDY8HC5PemN 3H89ld61kv1cg== 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 v4 03/25] fsverity: generate and store zero-block hash Date: Mon, 9 Mar 2026 20:23:18 +0100 Message-ID: <20260309192355.176980-4-aalbersh@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260309192355.176980-1-aalbersh@kernel.org> References: <20260309192355.176980-1-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