[DragonFlyBSD - Bug #3268] parent process does not receive POLLHUP events

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Mon May 10 17:16:47 PDT 2021


Issue #3268 has been updated by dillon.

File pollhup02.patch added

pollhup02.patch is a more complete patch (also removes unrelated cruft that was in my tree).  It patches the read and write side for pipes and for filesystem fifos.

-Matt

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Bug #3268: parent process does not receive POLLHUP events
http://bugs.dragonflybsd.org/issues/3268#change-13971

* Author: mikdusan
* Status: In Progress
* Priority: High
* Assignee: dillon
* Category: Userland
* Target version: Latest stable
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The attached `main.c` code is a reduction which takes as args, a command (absolute path) to fork/exec and poll stdout/stderr. POLLHUP events should be issued for both pipes when the child is finished.

For the Zig project we have this implemented in the zig language but I've provided a similar .c implementation since it was already done during my triage. For both .zig and .c code, linux, macos, freebsd, netbsd, openbsd work as expected and dragonfly manifests this unexpected behaviour of not receiving POLLHUP.

In the provided reduction, the bug manifests as an infinite loop after reading the bytes from child stdout/stderr. The parent keeps getting POLLIN events, and the read keeps returning 0 nbytes read which indicate the pipe has been closed. In the interim I will likely workaround this bug with conditional code for dragonfly to key off nbytes=0.

I have reproduced the bug on dragonfly 5.8, 6.0 and 5.0.0 (the oldest .iso I could find).

---Files--------------------------------
main.c (3.2 KB)
pollhup01.patch (357 Bytes)
pollhup02.patch (1.86 KB)


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