dev-libs/libevent: Disable signalfd by default in 2.2.1

Backport the upstream pull request that disables signalfd by default,
as it turned out to cause lots of unexpected breakage.  In particular,
app-misc/tmux was broken and it can't be trivially fixed.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

2 files changed, 159 insertions, 1 deletions

diff --git a/dev-libs/libevent/files/libevent-2.2.1-disable-signalfd.patch b/dev-libs/libevent/files/libevent-2.2.1-disable-signalfd.patch
new file mode 100644
index 000000000000..6dfce3db3497
--- /dev/null
+++ b/dev-libs/libevent/files/libevent-2.2.1-disable-signalfd.patch
@@ -0,0 +1,152 @@
+From 594ab34f1dfc73db85e8f95ec51892cadecaa76c Mon Sep 17 00:00:00 2001
+From: Azat Khuzhin <azat@libevent.org>
+Date: Mon, 10 Jul 2023 10:40:49 +0200
+Subject: [PATCH] Disable signalfd by default
+
+signalfd may behave differently to sigaction/signal, so to avoid
+breaking libevent users (like [1], [2]) disable it by default.
+
+  [1]: https://github.com/tmux/tmux/pull/3621
+  [2]: https://github.com/tmux/tmux/pull/3626
+
+Also signalfd is not that perfect:
+- you need to SIG_BLOCK the signal before
+  - blocked signals are not reset on exec
+  - blocked signals are allowed to coalesce - so in case of multiple
+    signals sent you may get the signal only once (ok for most of the
+    signals, but may be a problem for SIGCHLD, though you may call
+    waitpid() in a loop or use pidfd)
+- and also one implementation problem -
+  sigprocmask is unspecified in a multithreaded process
+
+Refs:
+- https://lwn.net/Articles/415684/
+- https://ldpreload.com/blog/signalfd-is-useless
+
+Refs: https://github.com/libevent/libevent/issues/1460
+Refs: #1342 (cc @dmantipov)
+---
+ CMakeLists.txt         |  1 +
+ include/event2/event.h |  6 ++++--
+ signalfd.c             |  4 ++--
+ test/include.am        |  2 ++
+ test/test.sh           | 11 +++++++++--
+ 5 files changed, 18 insertions(+), 6 deletions(-)
+
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index cd41d16e57..9c402ec0c1 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -1509,6 +1509,7 @@ if (NOT EVENT__DISABLE_TESTS)
+         else()
+             add_backend_test(${BACKEND} "${BACKEND_ENV_VARS}")
+         endif()
++        add_backend_test(signalfd_${BACKEND} "${BACKEND_ENV_VARS};EVENT_USE_SIGNALFD=1")
+     endforeach()
+ 
+     #
+diff --git a/include/event2/event.h b/include/event2/event.h
+index 384a84178b..9b971edf1d 100644
+--- a/include/event2/event.h
++++ b/include/event2/event.h
+@@ -599,9 +599,11 @@ enum event_base_config_flag {
+ 	 */
+ 	EVENT_BASE_FLAG_EPOLL_DISALLOW_TIMERFD = 0x40,
+ 
+-	/** Do not use signalfd(2) to handle signals even if supported.
++	/** Use signalfd(2) to handle signals over sigaction/signal.
++	 *
++	 * But note, that in some edge cases signalfd() may works differently.
+ 	 */
+-	EVENT_BASE_FLAG_DISALLOW_SIGNALFD = 0x80,
++	EVENT_BASE_FLAG_USE_SIGNALFD = 0x80,
+ };
+ 
+ /**
+diff --git a/signalfd.c b/signalfd.c
+index 376a04d539..ed31014e5f 100644
+--- a/signalfd.c
++++ b/signalfd.c
+@@ -205,8 +205,8 @@ sigfd_del(struct event_base *base, int signo, short old, short events, void *p)
+ int sigfd_init_(struct event_base *base)
+ {
+ 	EVUTIL_ASSERT(base != NULL);
+-	if ((base->flags & EVENT_BASE_FLAG_DISALLOW_SIGNALFD) ||
+-	    getenv("EVENT_DISALLOW_SIGNALFD"))
++	if (!(base->flags & EVENT_BASE_FLAG_USE_SIGNALFD) &&
++	    !getenv("EVENT_USE_SIGNALFD"))
+ 		return -1;
+ 	base->evsigsel = &sigfdops;
+ 	return 0;
+diff --git a/test/include.am b/test/include.am
+index e061c937b7..9b50759da7 100644
+--- a/test/include.am
++++ b/test/include.am
+@@ -80,6 +80,8 @@ test_runner_changelist: $(top_srcdir)/test/test.sh
+ 	$(top_srcdir)/test/test.sh -b "" -c
+ test_runner_timerfd_changelist: $(top_srcdir)/test/test.sh
+ 	$(top_srcdir)/test/test.sh -b "" -T
++test_runner_timerfd_changelist: $(top_srcdir)/test/test.sh
++	$(top_srcdir)/test/test.sh -b "" -S
+ 
+ DISTCLEANFILES += test/regress.gen.c test/regress.gen.h
+ 
+diff --git a/test/test.sh b/test/test.sh
+index dfdd2bf098..79362888c5 100755
+--- a/test/test.sh
++++ b/test/test.sh
+@@ -50,6 +50,7 @@ setup () {
+ 	done
+ 	unset EVENT_EPOLL_USE_CHANGELIST
+ 	unset EVENT_PRECISE_TIMER
++	unset EVENT_USE_SIGNALFD
+ }
+ 
+ announce () {
+@@ -138,10 +139,12 @@ do_test() {
+ 	    EVENT_EPOLL_USE_CHANGELIST=yes; export EVENT_EPOLL_USE_CHANGELIST
+ 	elif test "$2" = "(timerfd)" ; then
+ 	    EVENT_PRECISE_TIMER=1; export EVENT_PRECISE_TIMER
++	elif test "$2" = "(signalfd)" ; then
++	    EVENT_USE_SIGNALFD=1; export EVENT_USE_SIGNALFD
+ 	elif test "$2" = "(timerfd+changelist)" ; then
+ 	    EVENT_EPOLL_USE_CHANGELIST=yes; export EVENT_EPOLL_USE_CHANGELIST
+ 	    EVENT_PRECISE_TIMER=1; export EVENT_PRECISE_TIMER
+-        fi
++	fi
+ 
+ 	run_tests
+ }
+@@ -153,6 +156,7 @@ usage()
+   -t   - run timerfd test
+   -c   - run changelist test
+   -T   - run timerfd+changelist test
++  -S   - run signalfd test
+ EOL
+ }
+ main()
+@@ -161,13 +165,15 @@ main()
+ 	timerfd=0
+ 	changelist=0
+ 	timerfd_changelist=0
++	signalfd=0
+ 
+-	while getopts "b:tcT" c; do
++	while getopts "b:tcTS" c; do
+ 		case "$c" in
+ 			b) backends="$OPTARG";;
+ 			t) timerfd=1;;
+ 			c) changelist=1;;
+ 			T) timerfd_changelist=1;;
++			S) signalfd=1;;
+ 			?*) usage && exit 1;;
+ 		esac
+ 	done
+@@ -179,6 +185,7 @@ main()
+ 	[ $timerfd_changelist -eq 0 ] || do_test EPOLL "(timerfd+changelist)"
+ 	for i in $backends; do
+ 		do_test $i
++		[ $signalfd -eq 0 ] || do_test $i "(signalfd)"
+ 	done
+ 
+ 	if test "$FAILED" = "yes"; then
diff --git a/dev-libs/libevent/libevent-2.2.1-r1.ebuild b/dev-libs/libevent/libevent-2.2.1-r2.ebuild
index 63ff06976ccb..ea1d05922dfd 100644
--- a/dev-libs/libevent/libevent-2.2.1-r1.ebuild
+++ b/dev-libs/libevent/libevent-2.2.1-r2.ebuild
@@ -21,7 +21,7 @@ SRC_URI="
 S=${WORKDIR}/${MY_P}
 
 LICENSE="BSD"
-SLOT="0/2.2"
+SLOT="0/2.2.1-r2"
 KEYWORDS=""
 IUSE="
 	+clock-gettime debug malloc-replacement mbedtls +ssl static-libs
@@ -49,6 +49,12 @@ MULTILIB_WRAPPED_HEADERS=(
 )
 VERIFY_SIG_OPENPGP_KEY_PATH=${BROOT}/usr/share/openpgp-keys/libevent.asc
 
+PATCHES=(
+	# signalfd-by-default breaks at least app-misc/tmux
+	# https://github.com/libevent/libevent/pull/1486
+	"${FILESDIR}/${P}-disable-signalfd.patch"
+)
+
 multilib_src_configure() {
 	# fix out-of-source builds
 	mkdir -p test || die