linux-kernel - [PATCH] man2/splice.2: document SPLICE_F

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Date:   Tue, 26 Sep 2023 09:04:02 +0200
From:   Max Kellermann <max.kellermann@...os.com>
To:     alx@...nel.org, linux-man@...r.kernel.org, brauner@...nel.org,
        axboe@...nel.dk
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        libc-alpha@...rceware.org,
        Max Kellermann <max.kellermann@...os.com>
Subject: [PATCH] man2/splice.2: document SPLICE_F_NOWAIT

Patch for SPLICE_F_NOWAIT submitted to LKML:
 https://lore.kernel.org/lkml/20230926063609.2451260-1-max.kellermann@ionos.com/

In the HISTORY section, I declared Linux 6.7 as the first version to
have this feature, but this is only speculation, because
SPLICE_F_NOWAIT is still under discussion and has not yet been merged.

Signed-off-by: Max Kellermann <max.kellermann@...os.com>
---
 man2/splice.2 | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/man2/splice.2 b/man2/splice.2
index e9a18e668..1e686b858 100644
--- a/man2/splice.2
+++ b/man2/splice.2
@@ -89,13 +89,27 @@ call);
 in the future, a correct implementation may be restored.
 .TP
 .B SPLICE_F_NONBLOCK
-Do not block on I/O.
+Do not block on I/O on pipes.
 This makes the splice pipe operations nonblocking, but
 .BR splice ()
 may nevertheless block because the file descriptors that
 are spliced to/from may block (unless they have the
 .B O_NONBLOCK
-flag set).
+flag set or
+.B SPLICE_F_NOWAIT
+is specified).
+.TP
+.B SPLICE_F_NOWAIT
+If no data is immediately available on
+.I fd_in
+and it is not a pipe, do not wait (e.g. for backing storage or locks),
+but return immediately with
+.B EAGAIN.
+This is analogous to the
+.B RWF_NOWAIT
+flag of
+.BR preadv2()
+.
 .TP
 .B SPLICE_F_MORE
 More data will be coming in a subsequent splice.
@@ -138,6 +152,8 @@ is set to indicate the error.
 .TP
 .B EAGAIN
 .B SPLICE_F_NONBLOCK
+or
+.B SPLICE_F_NOWAIT
 was specified in
 .I flags
 or one of the file descriptors had been marked as nonblocking
@@ -192,6 +208,9 @@ was required to be a pipe.
 Since Linux 2.6.31,
 .\" commit 7c77f0b3f9208c339a4b40737bb2cb0f0319bb8d
 both arguments may refer to pipes.
+.PP
+.B SPLICE_F_NOWAIT
+was added in Linux 6.7.
 .SH NOTES
 The three system calls
 .BR splice (),
-- 
2.39.2