Re: [PATCH manpages v2 1/2] udp.7: add UDP_SEGMENT

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Willem,

On 3/2/23 16:48, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> UDP_SEGMENT was added in commit bec1f6f69736
> ("udp: generate gso with UDP_SEGMENT")
> 
>     $ git describe --contains bec1f6f69736
>     linux/v4.18-rc1~114^2~377^2~8
> 
> Kernel source has example code in tools/testing/selftests/net/udpgso*
> 
> Per https://www.kernel.org/doc/man-pages/patches.html,
> "Describe how you obtained the information in your patch":
> I am the author of the above commit and follow-ons.
> 
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Patch applied, with some minor tweaks and Simon's review tag.

Cheers,

Alex

> 
> ---
> 
> Changes v1->v2
>   - semantic newlines: also break on comma and colon
>   - remove bold: section number following function name
>   - add bold: special macro USHRT_MAX
> ---
>  man7/udp.7 | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/man7/udp.7 b/man7/udp.7
> index 5822bc551fdf..6646c1e96bb0 100644
> --- a/man7/udp.7
> +++ b/man7/udp.7
> @@ -204,6 +204,34 @@ portable.
>  .\"     UDP_ENCAP_ESPINUDP draft-ietf-ipsec-udp-encaps-06
>  .\"     UDP_ENCAP_L2TPINUDP rfc2661
>  .\" FIXME Document UDP_NO_CHECK6_TX and UDP_NO_CHECK6_RX, added in Linux 3.16
> +.TP
> +.BR UDP_SEGMENT " (since Linux 4.18)"
> +Enables UDP segmentation offload.
> +Segmentation offload reduces
> +.BR send (2)
> +cost by transferring multiple datagrams worth of data as a single large
> +packet through the kernel transmit path,
> +even when that exceeds MTU.
> +As late as possible,
> +the large packet is split by segment size into a series of datagrams.
> +This segmentation offload step is deferred to hardware if supported,
> +else performed in software.
> +This option takes a value between 0 and
> +.BR USHRT_MAX
> +that sets the segment size:
> +the size of datagram payload,
> +excluding the UDP header.
> +The segment size must be chosen such that at most 64 datagrams are sent in
> +a single call and that the datagrams after segmentation meet the same MTU
> +rules that apply to datagrams sent without this option.
> +Segmentation offload depends on checksum offload,
> +as datagram checksums are computed after segmentation.
> +The option may also be set for individual
> +.BR sendmsg (2)
> +calls by passing it as a
> +.BR cmsg (7).
> +A value of zero disables the feature.
> +This option should not be used in code intended to be portable.
>  .SS Ioctls
>  These ioctls can be accessed using
>  .BR ioctl (2).

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<http://www.alejandro-colomar.es/>
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