Support MSG_DONTWAIT in sendmsg()

[val_packett.cool]

Summary

Sometimes Weston (or any Wayland compositor really) would become unresponsive (whole UI frozen, mouse doesn't move) when a client (desktop app) became unresponsive. After some testing with procstat, the cause was found: sendmsg. Turns out libwayland-server was telling the kernel to not block on sendmsg, but the kernel wasn't listening.

https://gitlab.freedesktop.org/wayland/wayland/blob/921d0548035673a1bf6aeb9396b9bc728133411e/src/connection.c#L314-317

sendmsg(connection->fd, &msg, MSG_NOSIGNAL | MSG_DONTWAIT);

As a workaround MSG_NBIO can be used, but according to the comment it's intended for some fifo stuff. Let's support the correct constant that other operating systems support, e.g. OpenBSD does support it.

[markj]

This seems fine to me. sdp_sosend() needs the same treatment. sctp_sosend() probably does as well, but I don't see where. @tuexen might know.

sys/kern/uipc_socket.c

1525 ↗

(On Diff #52506)

You can test both flags at once: (flags & (MSG_DONTWAIT | MSG_NBIO)) != 0

[bcr]

OK from manpages, too.

[val_packett.cool]

sys/kern/uipc_socket.c

1525 ↗

(On Diff #52506)

oh, right, with !=0 it won't be a check for both, thanks for the tip

[val_packett.cool]

I think that's the right place in sctp. I'm not sure how to test it though, or the sdp thing…

[markj]

In D18728#399576, @greg_unrelenting.technology wrote:

I think that's the right place in sctp. I'm not sure how to test it though, or the sdp thing…

Thanks. Let's give @tuexen a day or two to weigh in on the SCTP side. sdp_sosend() is quite similar to sosend_generic(); I think it's fine to skip testing there.

sys/kern/uipc_socket.c

1525 ↗

(On Diff #52506)

The parens around the second condition are redundant, and the line is longer than 80 columns. I'd write

if ((so->so_state & SS_NBIO) != 0 ||
    (flags & (MSG_DONTWAIT | MSG_NBIO)) != 0) {
...

sys/netinet/sctp_output.c

12839 ↗

(On Diff #52513)

Redundant parens.

sys/ofed/drivers/infiniband/ulp/sdp/sdp_main.c

1127 ↗

(On Diff #52513)

Ditto.

[val_packett.cool]

Updated style.

BTW, would be nice to see this MFC'd into 12