RE: [PATCH] af_unix: closed SOCK_SEQPACKET socketpair must get SIGPIPE

[David Laight]

From: Alexander Potapenko
> Sent: 15 March 2016 09:04
> According to IEEE Std 1003.1, 2013, sending data to a SOCK_SEQPACKET
> socketpair with MSG_NOSIGNAL flag set must result in a SIGPIPE if the
> socket is no longer connected.
...
> Without the below patch the behavior is as follows:
> 
> $ ./sock seqpacket
> sendmsg: Broken pipe
...
> The behavior of the patched kernel complies with POSIX:
> 
> $  ./sock seqpacket
> Killed by SIGPIPE
...

While POSIX might specify this behaviour, changing the behaviour
could easily break applications.
Basically this change (more or less) require every application that
uses SOCK_SEQPACKED to be audited to ensure that MSG_NOSIGNAL is set
on ever send/write to the socket.

Personally I think the whole SIGPIPE on sockets should never have been
allowed to get into the standard.
I don't remember MSG_NOSIGNAL being present in SYSV.

The only time you want a write into a pipe to generate SIGPIPE is
for pipes generates by the shell that feed stdout to stdin of the
next process in the pipeline.
If pipes are implemented as unix-domain socketpairs (no one does that
any more) then it would require the SIGPIPE for write().

	David