linux-kernel - [PATCH 2/4] readv.2: Document RWF

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Message-Id: <20230929093717.2972367-3-john.g.garry@oracle.com>
Date:   Fri, 29 Sep 2023 09:37:15 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Cc:     martin.petersen@...cle.com, djwong@...nel.org, david@...morbit.com,
        himanshu.madhani@...cle.com, John Garry <john.g.garry@...cle.com>
Subject: [PATCH 2/4] readv.2: Document RWF_ATOMIC flag

From: Himanshu Madhani <himanshu.madhani@...cle.com>

Add RWF_ATOMIC flag description for pwritev2().

Signed-off-by: Himanshu Madhani <himanshu.madhani@...cle.com>
#jpg: complete rewrite
Signed-off-by: John Garry <john.g.garry@...cle.com>
---
 man2/readv.2 | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/man2/readv.2 b/man2/readv.2
index fa9b0e4e44a2..ff09f3bc9792 100644
--- a/man2/readv.2
+++ b/man2/readv.2
@@ -193,6 +193,51 @@ which provides lower latency, but may use additional resources.
 .B O_DIRECT
 flag.)
 .TP
+.BR RWF_ATOMIC " (since Linux 6.7)"
+Allows block-based filesystems to indicate that write operations will 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 between
+stx_atomic_write_unit_min and stx_atomic_write_unit_max, both inclusive. The
+write must be at a natural offset within the file with respect to the total
+write length. 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,
+.BR fdatasync (2)
+or
+.BR fsync (2)
+or
+.BR open (2)
+and
+.B O_SYNC
+or
+.B O_DSYNC
+or
+.B pwritev2 ()
+flag
+.B RWF_SYNC
+or
+.B RWF_DSYNC
+is required.
+For when regular files are opened with
+.BR open (2)
+but without
+.B O_SYNC
+or
+.B O_DSYNC
+and the
+.BR pwritev2()
+call is made without
+.B RWF_SYNC
+or
+.BR RWF_DSYNC
+set, the range metadata must already be flushed to storage and the data range
+must not be in unwritten state, shared, a preallocation, or a hole.
+.TP
 .BR RWF_SYNC " (since Linux 4.7)"
 .\" commit e864f39569f4092c2b2bc72c773b6e486c7e3bd9
 Provide a per-write equivalent of the
-- 
2.31.1