From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-202.mailbox.org (mout-p-202.mailbox.org [80.241.56.172]) (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 AEC3F47127D; Thu, 10 Sep 2026 11:20:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789039237; cv=none; b=AA6sTjBiQQWIDhsCQS0Ac9r77hP+J0E2N+icc8kJR/a59WusQ1/xz7fS8afLlEV6tsQg0Ywtqeuw7Eno95UZVLBJKh1lzuqBnRV5XyfmzgIrUliSIQSdRXizhP6MPq/XJhkDRSRqltX0nFPD7ICtMLQCkUio1bXFIw+vaokn/h8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789039237; c=relaxed/simple; bh=RCGYJEhBSAF5DE2tJhdVvO5rz8NP6FGV2iRExhOfowM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RbsNjj2W+3Ompfp4WptPeIuQF1ihu6xVt2BHWlPXvUOTXICsRaDnZf9nY7tnGT1QajbOQQG/OkMpgJLSugROShoEBZGjvBojRNned6HrI8TLB7EkHe0evcW5fVjwu3GmCyN3qr7GYX05EiJFDAUANzb5quOc3PkDLOkKBVO4bc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=samsung.com; spf=pass smtp.mailfrom=pankajraghav.com; arc=none smtp.client-ip=80.241.56.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=samsung.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pankajraghav.com Received: from smtp1.mailbox.org (smtp1.mailbox.org [IPv6:2001:67c:2050:b231:465::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-202.mailbox.org (Postfix) with ESMTPS id 4hgZwZ32K6zMlDk; Thu, 10 Sep 2026 13:20:30 +0200 (CEST) Authentication-Results: outgoing_mbo_mout; dkim=none; spf=pass (outgoing_mbo_mout: domain of kernel@pankajraghav.com designates 2001:67c:2050:b231:465::1 as permitted sender) smtp.mailfrom=kernel@pankajraghav.com From: Pankaj Raghav To: Alejandro Colomar , linux-man@vger.kernel.org Cc: pankaj.raghav@linux.dev, linux-xfs@vger.kernel.org, gost.dev@samsung.com, linux-ext4@vger.kernel.org, hch@lst.de, "Darrick J . Wong" , Zhang Yi , Pankaj Raghav Subject: [PATCH v3] man/man2/fallocate.2: Add doc for FALLOC_FL_WRITE_ZEROES Date: Thu, 10 Sep 2026 13:20:23 +0200 Message-ID: <20260910112023.2591987-1-p.raghav@samsung.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 4hgZwZ32K6zMlDk This flag was added to the kernel in v6.17. As of now, only ext4 and block device nodes support this flag. Cc: Zhang Yi Cc: Christoph Hellwig Cc: Darrick J. Wong Cc: gost.dev@samsung.com Cc: linux-ext4@vger.kernel.org Cc: linux-xfs@vger.kernel.org Signed-off-by: Pankaj Raghav --- Changes since v2: - Changed the commit format based on Alejandro's feedback. - I have retained "preallocated" term based on Zhang Yi's feedback[1] Note: This feature was recently added to XFS and it is expected to land in v7.3. I will update this man page again once v7.3 is released. [1] https://lore.kernel.org/linux-man/3f17d214-f69c-47b6-abf6-4437cc5840c0@huaweicloud.com/ man/man2/fallocate.2 | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/man/man2/fallocate.2 b/man/man2/fallocate.2 index ef6586c77..48a8c3468 100644 --- a/man/man2/fallocate.2 +++ b/man/man2/fallocate.2 @@ -244,6 +244,43 @@ SMB3 (since Linux 3.17) .IP \[bu] Btrfs (since Linux 4.16) .\" commit f27451f229966874a8793995b8e6b74326d125df +.SS Writing zeroes in file space +Specifying the +.B FALLOC_FL_WRITE_ZEROES +flag (available since Linux 6.17) +.\" commit 7bd43cc79cab3850f34da0a31d5b042b701590ef +in +.I mode +physically zeros space in the byte range starting at +.I offset +and continuing for +.I size +bytes. +Within the specified range, +blocks are preallocated for the regions that span the holes +in the file. +After a successful call, +subsequent reads from this range will return zeros and +subsequent writes to that range do not require further +changes to the file mapping metadata. +.P +Zeroing is done within the filesystem. +The filesystem may use a hardware-accelerated zeroing command +or may submit regular writes. +The behavior depends on the filesystem design and the +available hardware. +.P +No other flags may be specified in +.I mode +in conjunction with +.BR FALLOC_FL_WRITE_ZEROES . +.P +Not all filesystems support +.BR FALLOC_FL_WRITE_ZEROES ; +if a filesystem doesn't support the operation, an error is returned. +The operation is supported only in ext4 (only for extent-based files) +since Linux 6.17. +.\" commit f4265b8d32c49ff95711e6fef7d05245a2905b30 .SS Increasing file space Specifying the .B FALLOC_FL_INSERT_RANGE @@ -385,6 +422,7 @@ or is .BR FALLOC_FL_COLLAPSE_RANGE , .BR FALLOC_FL_ZERO_RANGE , +.BR FALLOC_FL_WRITE_ZEROES , or .BR FALLOC_FL_INSERT_RANGE , but the file referred to by base-commit: d926b42e0ea0406d5c2556e18205eced92d053f1 -- 2.51.2