Re: SO_SNDTIMEO: 2.4 kernel bugs

[kuznet@ms2.inr.ac.ru]

Hello!

> You are right - our sendfile() implementation is broken. I have fixed it

Thank you!


> Investigation shows that the Linux network layer is behaving oddly. It
> seems that we are writing 4096 bytes to a socket. This proceeds in 4096
> byte chunks until the send buffer on the socket is full, and a 4096 byte
> write blocks. This blocking write is eventually interrupted by the
> timeout, and the write call returns.. wait for it.. 4096! This suggests
> there was socket space after all, and the call should not have blocked.

Wakeup does not happen until _enough_ (1/3 of snbuf) of space in sndbuf
is released, otherwise you will overschedule. So, as soon as
write() goes to sleep, it will sleep waiting until 1/3 is released.

If it is interrupted, it use all the released space immediately before exit.
Again, to make more for in this context. This can be even wrong and, probably,
we should return instantly with -EAGAIN/-EINTR/partial count, but it is most
likely suboptimal (though I have already changed this to instant return).
But this does not look essential from caller's viewpoint, except for
sendfile() of course. 8)

Alexey