[patch v2] send.2: Add MSG_FASTOPEN flag

[patch v2] send.2: Add MSG_FASTOPEN flag

[Wei Wang]

MSG_FASTOPEN flag is available since Linux 3.7. Add detailed description
in the manpage according to RFC7413.

Signed-off-by: Wei Wang <weiwan@google.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
Change in v2: corrected some format issues

 man2/send.2 | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/man2/send.2 b/man2/send.2
index fd28fed90..acaa05be9 100644
--- a/man2/send.2
+++ b/man2/send.2
@@ -252,6 +252,38 @@ data on sockets that support this notion (e.g., of type
 the underlying protocol must also support
 .I out-of-band
 data.
+.TP
+.BR MSG_FASTOPEN " (since Linux 3.7)"
+Attempts TCP Fast Open (RFC7413) and sends data in the SYN like a
+combination of
+.BR connect (2)
+and
+.BR write (2),
+by performing an implicit
+.BR connect (2)
+operation.
+It blocks until the data is buffered and the handshake has completed.
+For a non-blocking socket,
+it returns the number of bytes buffered and sent in the SYN packet.
+If the cookie is not available locally,
+it returns
+.BR EINPROGRESS ,
+and sends a SYN with a Fast Open cookie request automatically.
+The caller needs to write the data again when the socket is connected.
+On errors,
+it sets the same
+.I errno
+as
+.BR connect (2)
+if the handshake fails.
+This flag requires enabling TCP Fast Open client support on sysctl
+.IR net.ipv4.tcp_fastopen .
+.IP
+Refer to
+.B TCP_FASTOPEN_CONNECT
+socket option in
+.BR tcp (7)
+for an alternative approach.
 .SS sendmsg()
 The definition of the
 .I msghdr
-- 
2.33.0.464.g1972c5931b-goog

Re: [patch v2] send.2: Add MSG_FASTOPEN flag

[Alejandro Colomar (man-pages)]

Hi Wei,

On 9/17/21 6:16 AM, Wei Wang wrote:
> MSG_FASTOPEN flag is available since Linux 3.7. Add detailed description
> in the manpage according to RFC7413.
> 
> Signed-off-by: Wei Wang <weiwan@google.com>
> Reviewed-by: Yuchung Cheng <ycheng@google.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>

Patch applied!

Thanks (and to the reviewers too!),

Alex

> ---
> Change in v2: corrected some format issues
> 
>   man2/send.2 | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/man2/send.2 b/man2/send.2
> index fd28fed90..acaa05be9 100644
> --- a/man2/send.2
> +++ b/man2/send.2
> @@ -252,6 +252,38 @@ data on sockets that support this notion (e.g., of type
>   the underlying protocol must also support
>   .I out-of-band
>   data.
> +.TP
> +.BR MSG_FASTOPEN " (since Linux 3.7)"
> +Attempts TCP Fast Open (RFC7413) and sends data in the SYN like a
> +combination of
> +.BR connect (2)
> +and
> +.BR write (2),
> +by performing an implicit
> +.BR connect (2)
> +operation.
> +It blocks until the data is buffered and the handshake has completed.
> +For a non-blocking socket,
> +it returns the number of bytes buffered and sent in the SYN packet.
> +If the cookie is not available locally,
> +it returns
> +.BR EINPROGRESS ,
> +and sends a SYN with a Fast Open cookie request automatically.
> +The caller needs to write the data again when the socket is connected.
> +On errors,
> +it sets the same
> +.I errno
> +as
> +.BR connect (2)
> +if the handshake fails.
> +This flag requires enabling TCP Fast Open client support on sysctl
> +.IR net.ipv4.tcp_fastopen .
> +.IP
> +Refer to
> +.B TCP_FASTOPEN_CONNECT
> +socket option in
> +.BR tcp (7)
> +for an alternative approach.
>   .SS sendmsg()
>   The definition of the
>   .I msghdr
> 


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/