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Mon, 22 Jul 2024 09:57:44 +0000 Received: from DM6PR10MB4313.namprd10.prod.outlook.com ([fe80::4f45:f4ab:121:e088]) by DM6PR10MB4313.namprd10.prod.outlook.com ([fe80::4f45:f4ab:121:e088%6]) with mapi id 15.20.7762.027; Mon, 22 Jul 2024 09:57:44 +0000 From: John Garry To: alx@kernel.org Cc: linux-man@vger.kernel.org, linux-fsdevel@vger.kernel.org, axboe@kernel.dk, hch@lst.de, djwong@kernel.org, dchinner@redhat.com, martin.petersen@oracle.com, Himanshu Madhani , John Garry Subject: [PATCH v5 2/3] readv.2: Document RWF_ATOMIC flag Date: Mon, 22 Jul 2024 09:57:22 +0000 Message-Id: <20240722095723.597846-3-john.g.garry@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20240722095723.597846-1-john.g.garry@oracle.com> References: <20240722095723.597846-1-john.g.garry@oracle.com> X-ClientProxiedBy: LO4P265CA0112.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:2c3::15) To DM6PR10MB4313.namprd10.prod.outlook.com (2603:10b6:5:212::20) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR10MB4313:EE_|PH0PR10MB5595:EE_ X-MS-Office365-Filtering-Correlation-Id: bae33a41-0d1e-4377-4e4e-08dcaa34bb60 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; 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Signed-off-by: Himanshu Madhani [jpg: complete rewrite] Signed-off-by: John Garry Reviewed-by: Darrick J. Wong --- man/man2/readv.2 | 61 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/man/man2/readv.2 b/man/man2/readv.2 index eecde06dc..7737eb65c 100644 --- a/man/man2/readv.2 +++ b/man/man2/readv.2 @@ -237,6 +237,50 @@ the data is always appended to the end of the file. However, if the .I offset argument is \-1, the current file offset is updated. +.TP +.BR RWF_ATOMIC " (since Linux 6.11)" +Requires that writes to regular files in block-based filesystems be issued with +torn-write protection. +Torn-write protection means that for a power or any other hardware failure, +all or none of the data from the write will be stored, +but never a mix of old and new data. +This flag is meaningful only for +.BR pwritev2 (), +and its effect applies only to the data range written by the system call. +The total write length must be power-of-2 and must be sized in the range +.RI [ stx_atomic_write_unit_min , +.IR stx_atomic_write_unit_max ]. +The write must be at a naturally-aligned offset within the file with respect to +the total write length. +For example, +a write of length 32KiB at a file offset of 32KiB is permitted, +however a write of length 32KiB at a file offset of 48KiB is not permitted. +The upper limit of +.I iovcnt +for +.BR pwritev2 () +is given by the value in +.I stx_atomic_write_segments_max. +Torn-write protection only works with +.B O_DIRECT +flag, +i.e. buffered writes are not supported. +To guarantee consistency from the write between a file's in-core state with the +storage device, +.B O_SYNC +or +.B O_DSYNC +must be specified for +.BR open (2). +The same synchronized I/O guarantees as described in +.BR open (2) +are provided when these flags or their equivalent flags and system calls are +used (e.g. +if +.BR RWF_SYNC +is specified for +.BR pwritev2 () +). .SH RETURN VALUE On success, .BR readv (), @@ -280,9 +324,26 @@ values overflows an value. .TP .B EINVAL +If +.BR RWF_ATOMIC +is specified, +the combination of the sum of the +.I iov_len +values and the +.I offset +value does not comply with the length and offset torn-write protection rules. +.TP +.B EINVAL The vector count, .IR iovcnt , is less than zero or greater than the permitted maximum. +If +.BR RWF_ATOMIC +is specified, +this maximum is given by the +.I stx_atomic_write_segments_max +value from +.I statx. .TP .B EOPNOTSUPP An unknown flag is specified in \fIflags\fP.