util.signal: Add support for signalfd(2) on Linux

signalfd allows handling signal events using the same method as sockets,
via file descriptors. Thus all signal dispatch can go through the same
main event loop as everything else, removing need for thread-scary
signal handling where execution would just jump to the signal handler
regardless of the state of Lua, and needing to keep track of Lua
states/threads.

1 files changed, 34 insertions, 0 deletions

diff --git a/util-src/signal.c b/util-src/signal.c
index a55b6f87..3af80a73 100644
--- a/util-src/signal.c
+++ b/util-src/signal.c
@@ -32,6 +32,10 @@
 
 #include <signal.h>
 #include <stdlib.h>
+#ifdef __linux__
+#include <unistd.h>
+#include <sys/signalfd.h>
+#endif
 
 #include "lua.h"
 #include "lauxlib.h"
@@ -368,12 +372,42 @@ static int l_kill(lua_State *L) {
 
 #endif
 
+#ifdef __linux__
+static int l_signalfd(lua_State *L) {
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, luaL_checkinteger(L, 1));
+
+	sigprocmask(SIG_BLOCK, &mask, NULL); /* TODO check err */
+
+	lua_pushinteger(L, signalfd(-1, &mask, SFD_NONBLOCK));
+	return 1;
+}
+
+static int l_signalfd_read(lua_State *L) {
+	const int sigfd = luaL_checkinteger(L, 1);
+	struct signalfd_siginfo siginfo;
+
+	if(read(sigfd, &siginfo, sizeof(siginfo)) < 0) {
+		return 0;
+	}
+
+	lua_pushinteger(L, siginfo.ssi_signo);
+	return 1;
+}
+#endif
+
 static const struct luaL_Reg lsignal_lib[] = {
 	{"signal", l_signal},
 	{"raise", l_raise},
 #if defined(__unix__) || defined(__APPLE__)
 	{"kill", l_kill},
 #endif
+#ifdef __linux__
+	{"signalfd", l_signalfd},
+	{"signalfd_read", l_signalfd_read},
+#endif
 	{NULL, NULL}
 };