Re: [RFC net-next af_unix v1 0/1] Allow delivery of SIGURG on AF_UNIX streams socket

[Matthew Wilcox <willy@infradead.org>]

On Mon, Dec 07, 2020 at 09:00:12AM -0800, Andy Lutomirski wrote:
> >> I'm also a bit nervous that there might be some program out there that
> >> expects SIGIO but not SIGURG on unix sockets, and you're breaking
> >> them.
> > 
> > The only incompatible scenario I've been able to think of is an
> > application which has both TCP and Unix sockets will suddenly get its
> > SIGURG handler called for Unix sockets when it's only expecting to get
> > it called for TCP sockets.  That feels like a very unlikely scenario.
> 
> So maybe this is okay. It does seem like a hack, but maybe it’s a hack that’s not too bad to support in the kernel.

I see it as extending a (somewhat bogus) TCP socket API to Unix sockets.
The mechanism is badly named.  If it were called MSG_URG instead of
MSG_OOB, I think it'd be a lot less objectionable.  Apparently the
sockets people were enamoured with the idea of having multiple streams
of data inside a single socket, which is madness.

I'd really like a way to generate SIGURG on pipes too, but that's harder
to wire up.