Where is setsockopt() defined?

Where is setsockopt() defined?

[Peng Yu]

https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/socket/sys/socket.h#L215

I see setsockopt() is declared above. But I don't find its source
code. Where is it defined? Thanks.

https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/socket/setsockopt.c

-- 
Regards,
Peng

Re: Where is setsockopt() defined?

[Florian Weimer]

* Peng Yu via Libc-help:

> https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/socket/sys/socket.h#L215
>
> I see setsockopt() is declared above. But I don't find its source
> code. Where is it defined? Thanks.

It's in sysdeps/unix/sysv/linux/setsockopt.c.

Florian

Re: Where is setsockopt() defined?

[Peng Yu]

> It's in sysdeps/unix/sysv/linux/setsockopt.c.

https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/sysdeps/unix/sysv/linux/setsockopt.c

There is not much code in this file. Based on the manpage of
setsockopt() (which refers to socket(7)), setsockopt() should be able
to process many different cases. So I'd expect many branch statements.
Where are they defined?

Things like INLINE_SYSCALL and SOCKETCALL are too complicated to
comprehend. How to understand what they do?

https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/sysdeps/unix/sysv/linux/sysdep.h#L42
https://github.com/bminor/glibc/blob/83908b3a1ea51e3aa7ff422275940e56dbba989f/sysdeps/unix/sysv/linux/socketcall.h#L85

-- 
Regards,
Peng

Re: Where is setsockopt() defined?

[Konstantin Kharlamov]

On Wed, 2021-03-03 at 00:14 -0600, Peng Yu via Libc-help wrote:
> > It's in sysdeps/unix/sysv/linux/setsockopt.c.
> 
> https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/sysdeps/unix/sysv/linux/setsockopt.c
> 
> There is not much code in this file. Based on the manpage of
> setsockopt() (which refers to socket(7)), setsockopt() should be able
> to process many different cases. So I'd expect many branch statements.
> Where are they defined?
> 
> Things like INLINE_SYSCALL and SOCKETCALL are too complicated to
> comprehend. How to understand what they do?
> 
> https://github.com/bminor/glibc/blob/21c3f4b5368686ade28d90d8c7d79c4c95c72c1b/sysdeps/unix/sysv/linux/sysdep.h#L42
> https://github.com/bminor/glibc/blob/83908b3a1ea51e3aa7ff422275940e56dbba989f/sysdeps/unix/sysv/linux/socketcall.h#L85


(disclaimer: I'm not a glibc dev)

The INLINE_SYSCALL as it name says is apparently syscall. A syscall simply places its arguments into registers/stack as defined by the architecture and calls into kernel.

The SOCKETCALL version indeed looks involved, but as far I as see it just basically chooses between __SOCKETCALL1..__SOCKETCALL6 macroses based on the number of arguments. And all 6 of those, in turn, are a wrapper around INLINE_SYSCALL.

So, all roads lead to Rome aka kernel.