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

On Mon, Dec 07, 2020 at 09:00:12AM -0800, Andy Lutomirski wrote:

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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.