Track armed events in muxnotes closely

[MadCoder]

This fixes issues around resuming or re-registering file-descriptors with
a previously triggered EPOLLONESHOT event.

Signed-off-by: Pierre Habouzit phabouzit@apple.com
Fixes: SR-5759

[MadCoder]

@swift-ci please test

[MadCoder]

I'd appreciate a review from someone, @weissi (who is on vacation atm) has indepdently checked that it fixes SR-5759 for him.

the problem with epoll is that what is two different filters in the kevent world (EVFILT_READ/EVFILT_WRITE) is really a single one in epoll.

the multiplexing code which is a simplified version of the kevent one assumes that the first source that is resumed, resumes the multiplexing note, and that delivery disables it fully. However this is not quite how it works, we need to be able to do partial resumes/disarm of EPOLLIN and EPOLLOUT independently as all write sources of a given fd could be suspended while read sources are active and vice versa.

[MadCoder]

Note: this is slated for swift4 too

[dgrove-oss]

was out on vacation last week; will take a look at this tomorrow (unburying from other stuff today). Sorry for the delay.

[jblache]

LGTM

No regression against our codebase.

[MadCoder]

@dgrove-oss no worries, this isn't even a day old ;) I'll wait for you to have a look then.

[dgrove-oss]

The fix makes sense to me and generally looks good. It just needs one small tweak to compile with the additional compilation warnings enabled when using CMake. The type of the local variable filter in _dispatch_muxnote_create needs to be updated to match the change of du_filter from intt_16 to intt_8. Patch below:

diff --git a/src/event/event_epoll.c b/src/event/event_epoll.c
index 6e4c29a..323772c 100644
--- a/src/event/event_epoll.c
+++ b/src/event/event_epoll.c
@@ -151,7 +151,7 @@ _dispatch_muxnote_create(dispatch_unote_t du, uint32_t events)
        dispatch_muxnote_t dmn;
        struct stat sb;
        int fd = (int)du._du->du_ident;
-       int16_t filter = du._du->du_filter;
+       int8_t filter = du._du->du_filter;
        bool skip_outq_ioctl = false, skip_inq_ioctl = false;
        sigset_t sigmask;