Re: Lack of Documentation about SA_RESTART...

Theodore Ts'o
2005-07-12T18:19:59Z

On Tue, Jul 12, 2005 at 05:25:04PM +0200, Paolo Ornati wrote:
> Hmmm... no, no. A connect() on non-blocking socket will NEVER return
> EINTR. SUSV3 and Linux code agree.
>
> A syscall isn't magically interrupted if a signal arrives... it's the
> syscall that must check for pending signals and do the proper action
> (usually it will return with -EINTR or -ERESTARTSYS).
>
> A connect() on a blocking socket is something like this (very
> approssimative):
>
> 1) code to activate the connection
> 2) sleep waiting for something (connection ready / signal received...)
> 3) if connection is ready then return 0, else if there are pending
> signals return -ERESTARTSYS
>
> With non-blocking socket the syscall never sleeps, and never checks for
> pending signals.
>
> Look at "net/ipv4/af_inet.c": in particular at "net_wait_for_connect"
> and its usage in "inet_stream_connect".

Yes, do look at that. From the latest 2.6 sources:

timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);

if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
/* Error code is set above */
if (!timeo || !inet_wait_for_connect(sk, timeo))
goto out;

err = sock_intr_errno(timeo);
if (signal_pending(current))
goto out;
}

If the socket is non-blocking, then we don't call
inet_wiat_for_connect(), yes. But sock_intr_errno() will set the
error code to -EINTR if the socket is set to non-nonblocking (see
include/net/sock.h), and if a signal is pending, return it.

- Ted