SO_NO_CHECK socket option

SO_NO_CHECK socket option

[Johannes Stezenbach]

Hi,

according to RFC 768 the UDP checksum is optional, and
indeed the kernel has support for the SO_NO_CHECK socket
option (boolean: 0 == default, calculate checksum on xmit,
1 == do not calculate checksum on xmit).

Maybe you would like to add this to socket(7).


Thanks
Johannes
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Re: SO_NO_CHECK socket option

[Michael Kerrisk]

Hello Johannes,

On Fri, Aug 20, 2010 at 7:49 PM, Johannes Stezenbach <js-FF7aIK3TAVNeoWH0uzbU5w@public.gmane.org> wrote:
> Hi,
>
> according to RFC 768 the UDP checksum is optional, and
> indeed the kernel has support for the SO_NO_CHECK socket
> option (boolean: 0 == default, calculate checksum on xmit,
> 1 == do not calculate checksum on xmit).
>
> Maybe you would like to add this to socket(7).

In the source of the socket.7 man page, there is a comment:

[[

]]
One of the coauthors of this page was Andi Kleen, and I suspect he
wrote the comment


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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Re: SO_NO_CHECK socket option

[Michael Kerrisk]

[Hit send to soon on the last reply...]

Hello Johannes,

On Fri, Aug 20, 2010 at 7:49 PM, Johannes Stezenbach <js-FF7aIK3TAVNeoWH0uzbU5w@public.gmane.org> wrote:
> Hi,
>
> according to RFC 768 the UDP checksum is optional, and
> indeed the kernel has support for the SO_NO_CHECK socket
> option (boolean: 0 == default, calculate checksum on xmit,
> 1 == do not calculate checksum on xmit).
>
> Maybe you would like to add this to socket(7).

In the source of the socket.7 man page, there is a comment:

[[
.\" don't document it because it can do too much harm.
.\".B SO_NO_CHECK

]]

One of the coauthors of this page was Andi Kleen, and I suspect he
wrote the comment. Given that Andi knows far more about the socket
stack than I, I am reluctant to make any change. But perhaps Andi can
comment further.

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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Re: SO_NO_CHECK socket option

[Andi Kleen]

>
> In the source of the socket.7 man page, there is a comment:
>
> [[
> .\" don't document it because it can do too much harm.
> .\".B SO_NO_CHECK
>
> ]]
>
> One of the coauthors of this page was Andi Kleen, and I suspect he
> wrote the comment. Given that Andi knows far more about the socket
> stack than I, I am reluctant to make any change. But perhaps Andi can
> comment further.

On Linux UDP checksums are essentially free and there's no reason
to turn them off and it would disable another safety line.
That is why I didn't document the option.

-Andi

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