Date: Sun, 02 Aug 2020 23:20:02 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 248440] kevent not returning full pipes registered with EVFILT_WRITE when on read end closure Message-ID: <bug-248440-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248440 Bug ID: 248440 Summary: kevent not returning full pipes registered with EVFILT_WRITE when on read end closure Product: Base System Version: 12.1-RELEASE Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: larkinconr@gmail.com Attachment #216970 text/plain mime type: Created attachment 216970 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=216970&action=edit test program to reproduce bug via filling/monitoring stdout When using kevent to monitor the write end of a pipe for writability via EVFILT_WRITE, if the pipe is full when the read end is closed, an event is not returned. I would expect an event with EV_EOF set to be returned. Note that this does not seem to reproduce with sockets or named pipes (fifos), those return an event with EV_EOF set just fine in this situation. I'm attaching a sample program that verifies stdout is a pipe and then attempts to fill it with data, then waits for an event with EVFILT_WRITE for stdout. If you pipe this to some program that doesn't read stdin, for instance sleep(1), the pipeline hangs forever. Notably, if you instead redirect its output to a named pipe and have sleep "read" the named pipe with shell redirection, the program *does* receive an event for stdout with EV_EOF set once sleep exits. I originally detected this with a test case that creates a pipe via pipe(2) in process, so testing with socketpair(2) was convenient, but it used threads and other infrastructure etc so I wrote a new test program. But I just want to mention that because it would seem to exclude some weird interaction with my shell etc. Example test case using the attached kqwrite.c: $ ./kqwrite | /bin/sleep 1 # hangs forever ^C $ mkfifo dummy; /bin/sleep 1 < dummy &; ./kqwrite > dummy # returns EV_EOF: [1] 1734 kevent returned 1 1 -2 32768 0 0 0x0 [1] + done /bin/sleep 1 < dummy -- You are receiving this mail because: You are the assignee for the bug.help
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