signal: new signal handling backend based on signalfd

Linux-specific signal handling backend based on signalfd(2) system call, and public function event_base_get_signal_method() to obtain an underlying kernel signal handling mechanism. Signed-off-by: Dmitry Antipov <[email protected]>
Hotant-Bu · Nov 12, 2022 · 1af745d · 1af745d
1 parent 9e34693
commit 1af745d
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Showing 14 changed files with 306 additions and 23 deletions.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -450,6 +450,7 @@ else()
         sys/wait.h
         sys/resource.h
         sys/timerfd.h
+        sys/signalfd.h
         netinet/in.h
         netinet/in6.h
         netinet/tcp.h
@@ -583,6 +584,7 @@ list(APPEND CMAKE_EXTRA_INCLUDE_FILES ${EVENT_INCLUDES} stdio.h)
 CHECK_SYMBOLS_EXIST("${SYMBOLS_TO_CHECK}" "${CMAKE_EXTRA_INCLUDE_FILES}" "EVENT")
 unset(SYMBOLS_TO_CHECK)
 set(EVENT__HAVE_EPOLL ${EVENT__HAVE_EPOLL_CREATE})
+set(EVENT__HAVE_SIGNALFD ${EVENT__HAVE_SYS_SIGNALFD_H})
 if(WIN32 AND NOT CYGWIN)
     set(EVENT__HAVE_WEPOLL 1)
 endif()
@@ -904,6 +906,10 @@ if(EVENT__HAVE_EPOLL)
     list(APPEND SRC_CORE epoll.c)
 endif()
 
+if(EVENT__HAVE_SIGNALFD)
+    list(APPEND SRC_CORE signalfd.c)
+endif()
+
 if(EVENT__HAVE_WEPOLL)
     list(APPEND SRC_CORE
         epoll.c

diff --git a/Makefile.am b/Makefile.am
@@ -229,6 +229,9 @@ endif
 if SIGNAL_SUPPORT
 SYS_SRC += signal.c
 endif
+if SIGNALFD_SUPPORT
+SYS_SRC += signalfd.c
+endif
 
 BUILT_SOURCES += include/event2/event-config.h
 

diff --git a/configure.ac b/configure.ac
@@ -181,7 +181,7 @@ LIBEVENT_OPENSSL
 LIBEVENT_MBEDTLS
 
 dnl Checks for header files.
-AC_CHECK_HEADERS([arpa/inet.h fcntl.h ifaddrs.h mach/mach_time.h mach/mach.h netdb.h netinet/in.h netinet/in6.h netinet/tcp.h sys/un.h poll.h port.h stdarg.h stddef.h sys/devpoll.h sys/epoll.h sys/event.h sys/eventfd.h sys/ioctl.h sys/mman.h sys/param.h sys/queue.h sys/resource.h sys/select.h sys/sendfile.h sys/socket.h sys/stat.h sys/time.h sys/timerfd.h sys/uio.h sys/wait.h sys/random.h errno.h afunix.h])
+AC_CHECK_HEADERS([arpa/inet.h fcntl.h ifaddrs.h mach/mach_time.h mach/mach.h netdb.h netinet/in.h netinet/in6.h netinet/tcp.h sys/un.h poll.h port.h stdarg.h stddef.h sys/devpoll.h sys/epoll.h sys/event.h sys/eventfd.h sys/ioctl.h sys/mman.h sys/param.h sys/queue.h sys/resource.h sys/select.h sys/sendfile.h sys/socket.h sys/stat.h sys/time.h sys/timerfd.h sys/signalfd.h sys/uio.h sys/wait.h sys/random.h errno.h afunix.h])
 
 case "${host_os}" in
     linux*) ;;
@@ -543,6 +543,7 @@ if test "$bwin32" = "true"; then
 fi
 AM_CONDITIONAL(WEPOLL_BACKEND, [test "$havewepoll" = "yes"])
 AM_CONDITIONAL(SIGNAL_SUPPORT, [test "$needsignal" = "yes"])
+AM_CONDITIONAL(SIGNALFD_SUPPORT, [test "$ac_cv_header_sys_signalfd_h" = "yes"])
 
 AC_TYPE_PID_T
 AC_TYPE_SIZE_T

diff --git a/epoll.c b/epoll.c
@@ -255,7 +255,8 @@ epoll_init(struct event_base *base)
 	}
 #endif
 
-	evsig_init_(base);
+	if (sigfd_init_(base) < 0)
+		evsig_init_(base);
 
 	return (epollop);
 }

diff --git a/event-config.h.cmake b/event-config.h.cmake
@@ -394,6 +394,9 @@
 /* Define to 1 if you have the <sys/timerfd.h> header file. */
 #cmakedefine EVENT__HAVE_SYS_TIMERFD_H 1
 
+/* Define to 1 if you have the <sys/signalfd.h> header file. */
+#cmakedefine EVENT__HAVE_SYS_SIGNALFD_H 1
+
 /* Define to 1 if you have the <sys/time.h> header file. */
 #cmakedefine EVENT__HAVE_SYS_TIME_H 1
 

diff --git a/event.c b/event.c
@@ -1860,6 +1860,13 @@ event_base_get_method(const struct event_base *base)
 	return (base->evsel->name);
 }
 
+const char *
+event_base_get_signal_method(const struct event_base *base)
+{
+	EVUTIL_ASSERT(base);
+	return (base->evsigsel->name);
+}
+
 /** Callback: used to implement event_base_loopexit by telling the event_base
  * that it's time to exit its loop. */
 static void

diff --git a/evmap.c b/evmap.c
@@ -465,7 +465,7 @@ evmap_signal_add_(struct event_base *base, int sig, struct event *ev)
 	    base->evsigsel->fdinfo_len);
 
 	if (LIST_EMPTY(&ctx->events)) {
-		if (evsel->add(base, ev->ev_fd, 0, EV_SIGNAL, NULL)
+		if (evsel->add(base, ev->ev_fd, 0, EV_SIGNAL, ev)
 		    == -1)
 			return (-1);
 	}
@@ -643,7 +643,8 @@ evmap_signal_reinit_iter_fn(struct event_base *base,
 	int *result = arg;
 
 	if (!LIST_EMPTY(&ctx->events)) {
-		if (evsel->add(base, signum, 0, EV_SIGNAL, NULL) == -1)
+		if (evsel->add(base, signum, 1, EV_SIGNAL,
+			       LIST_FIRST(&ctx->events)) == -1)
 			*result = -1;
 	}
 	return 0;

diff --git a/evsignal-internal.h b/evsignal-internal.h
@@ -45,6 +45,10 @@ struct evsig_info {
 	int ev_signal_added;
 	/* Count of the number of signals we're currently watching. */
 	int ev_n_signals_added;
+#ifdef EVENT__HAVE_SYS_SIGNALFD_H
+	/* EV_READ events used to wakeup corresponding EV_SIGNAL ones. */
+	struct event *ev_sigevent[NSIG];
+#endif /* EVENT__HAVE_SYS_SIGNALFD_H */
 
 	/* Array of previous signal handler objects before Libevent started
 	 * messing with them.  Used to restore old signal handlers. */
@@ -56,8 +60,17 @@ struct evsig_info {
 	/* Size of sh_old. */
 	int sh_old_max;
 };
+
+#ifdef EVENT__HAVE_SYS_SIGNALFD_H
+int sigfd_init_(struct event_base *);
+#else /* no signalfd() */
+static inline int
+sigfd_init_(struct event_base *base) { return -1; }
+#endif /* have signalfd() */
+
 int evsig_init_(struct event_base *);
 void evsig_dealloc_(struct event_base *);
+int evsig_ensure_saved_(struct evsig_info *, int);
 
 void evsig_set_base_(struct event_base *base);
 void evsig_free_globals_(void);

diff --git a/include/event2/event.h b/include/event2/event.h
@@ -381,6 +381,18 @@ int event_base_dispatch(struct event_base *base);
 EVENT2_EXPORT_SYMBOL
 const char *event_base_get_method(const struct event_base *eb);
 
+/**
+ Get the kernel signal handling mechanism used by Libevent.
+
+ @param eb the event_base structure returned by event_base_new()
+ @return a string identifying the kernel signal handling mechanism,
+   which is "signal" for traditional UNIX signal handlers,
+   "kqueue_signal" for kqueue(2)-based method on *BSD and macOS,
+   and "signalfd_signal" for Linux-only signalfd(2)-based method.
+ */
+EVENT2_EXPORT_SYMBOL
+const char *event_base_get_signal_method(const struct event_base *eb);
+
 /**
    Gets all event notification mechanisms supported by Libevent.
 
@@ -586,6 +598,10 @@ enum event_base_config_flag {
 	    epoll and if you do not have EVENT_BASE_FLAG_PRECISE_TIMER enabled.
 	 */
 	EVENT_BASE_FLAG_EPOLL_DISALLOW_TIMERFD = 0x40,
+
+	/** Do not use signalfd(2) to handle signals even if supported.
+	 */
+	EVENT_BASE_FLAG_DISALLOW_SIGNALFD = 0x80,
 };
 
 /**

diff --git a/poll.c b/poll.c
@@ -103,7 +103,8 @@ poll_init(struct event_base *base)
 	if (!(pollop = mm_calloc(1, sizeof(struct pollop))))
 		return (NULL);
 
-	evsig_init_(base);
+	if (sigfd_init_(base) < 0)
+		evsig_init_(base);
 
 	evutil_weakrand_seed_(&base->weakrand_seed, 0);
 

diff --git a/select.c b/select.c
@@ -119,7 +119,8 @@ select_init(struct event_base *base)
 		return (NULL);
 	}
 
-	evsig_init_(base);
+	if (sigfd_init_(base) < 0)
+		evsig_init_(base);
 
 	evutil_weakrand_seed_(&base->weakrand_seed, 0);
 

diff --git a/signal.c b/signal.c
@@ -208,25 +208,13 @@ evsig_init_(struct event_base *base)
 	return 0;
 }
 
-/* Helper: set the signal handler for evsignal to handler in base, so that
- * we can restore the original handler when we clear the current one. */
+/* Helper: resize saved signal handler array up to the highest signal
+   number. A dynamic array is used to keep footprint on the low side. */
 int
-evsig_set_handler_(struct event_base *base,
-    int evsignal, void (__cdecl *handler)(int))
+evsig_ensure_saved_(struct evsig_info *sig, int evsignal)
 {
-#ifdef EVENT__HAVE_SIGACTION
-	struct sigaction sa;
-#else
-	ev_sighandler_t sh;
-#endif
-	struct evsig_info *sig = &base->sig;
-	void *p;
-
-	/*
-	 * resize saved signal handler array up to the highest signal number.
-	 * a dynamic array is used to keep footprint on the low side.
-	 */
 	if (evsignal >= sig->sh_old_max) {
+		void *p;
 		int new_max = evsignal + 1;
 		event_debug(("%s: evsignal (%d) >= sh_old_max (%d), resizing",
 			    __func__, evsignal, sig->sh_old_max));
@@ -242,6 +230,25 @@ evsig_set_handler_(struct event_base *base,
 		sig->sh_old_max = new_max;
 		sig->sh_old = p;
 	}
+	return 0;
+}
+
+/* Helper: set the signal handler for evsignal to handler in base, so that
+ * we can restore the original handler when we clear the current one. */
+int
+evsig_set_handler_(struct event_base *base,
+    int evsignal, void (__cdecl *handler)(int))
+{
+#ifdef EVENT__HAVE_SIGACTION
+	struct sigaction sa;
+#else
+	ev_sighandler_t sh;
+#endif
+	struct evsig_info *sig = &base->sig;
+
+	/* ensure saved array is large enough */
+	if (evsig_ensure_saved_(sig, evsignal) < 0)
+		return (-1);
 
 	/* allocate space for previous handler out of dynamic array */
 	sig->sh_old[evsignal] = mm_malloc(sizeof *sig->sh_old[evsignal]);