On Tue, Apr 11, 2017 at 06:51:06PM -0300, Marcelo Ricardo Leitner wrote:
> On Wed, Apr 12, 2017 at 01:54:41AM +0530, Deepak Khandelwal wrote:
> > Hi,
> >
>
> Please don't top post..
>
> >
> > App act as client (1-1 Style SOCK_STREAM)
> > App try to send 278 bytes of message.
>
> Okay.
>
> >
> > So you mean that, if socket has space for few bytes (say 1 or 2
> > bytes), lksctp will set POLLOUT event for fd,
> > but since user application doesn;t know the underlying socket space
> > available, it can write more than that but will fail with EAGAIN ?
>
> Was reading the code again on this, I actually don't think this can
> happen. The sleep on waiting for sndbuf doesn't check for msgsize, just
> if there is any amount of buffer available or not.
>
> sctp_sendmsg()
> {
> ...
> timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
> if (!sctp_wspace(asoc)) {
> err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len);
> if (err)
> goto out_free;
> }
> ...
> }
>
> For returning -EAGAIN due to sndbuf, it has to match !sctp_wspace, which
> is only about the soc/asoc and not the message. The EAGAIN in this case
> comes from inside sctp_wait_for_sndbuf().
>
> That leads us to my other question, are you binding/connecting this
> socket before sending the message?
>
This was my thought. sctp_wait_for_sndbuf actually doesn't appear to be able to
return EAGAIN from my read. The only place I see it getting retured from the
socket layer in the sctp codes sendmsg path is if the socket hasn't been bound
and autobind fails.
Neil
> >
> >
> > Best Regards,
> > Deepak
> >
> > On Wed, Apr 12, 2017 at 12:44 AM, Michael Tuexen
> > <Michael.Tuexen@xxxxxxxxxxxxxxxxx> wrote:
> > >> On 11. Apr 2017, at 21:08, Deepak Khandelwal <dazz.87@xxxxxxxxx> wrote:
> > >>
> > >> Hi,
> > >>
> > >> I am using 4.4.x kernel.
> > >>
> > >> in context of LKSCTP, what could be the possible reasons that poll or
> > >> select on fd return false positive events, causing application do
> > >> write on fd but failed with EAGAIN ?
> > > I'm just guessing here... What if you can write something, but not
> > > something big as you try...
> > > So how big is the message you are trying so send?
> > >
> > > Best regards
> > > Michael
> > >>
> > >>
> > >> Best Regards,
> > >> Deepak
> > >> --
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