udevd: use ppoll instead of signal pipes

udevd uses a rather old-fashioned way of handling signals
while waiting for input through select (ie by using an unnamed
pipe, to which the signal handler writes one byte for every signal
received). This is rather awkward and may potentially even block
if we receive more signals than the kernel's pipe buffer.

This patch replaces all of that with ppoll, which was designed
for this purpose.

It also removes the SA_RESTART flag from all installed signal
handlers, because otherwise the ppoll call would just be restarted
after handling eg a SIGCHLD.

Signed-off-by: Olaf Kirch <okir@suse.de>

1 files changed, 35 insertions, 64 deletions

diff --git a/udev/udevd.c b/udev/udevd.c
index 993964d23d..bc6484b1b0 100644
--- a/udev/udevd.c
+++ b/udev/udevd.c
@@ -29,6 +29,7 @@
 #include <getopt.h>
 #include <dirent.h>
 #include <sys/select.h>
+#include <sys/poll.h>
 #include <sys/wait.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>
@@ -63,10 +64,10 @@ static struct udev_rules *rules;
 static struct udev_ctrl *udev_ctrl;
 static struct udev_monitor *kernel_monitor;
 static int inotify_fd = -1;
-static int signal_pipe[2] = {-1, -1};
 static volatile int sigchilds_waiting;
 static volatile int udev_exit;
 static volatile int reload_config;
+static volatile int signal_received;
 static int run_exec_q;
 static int stop_exec_q;
 static int max_childs;
@@ -194,8 +195,6 @@ static void event_fork(struct udev_event *event)
 		udev_ctrl_unref(udev_ctrl);
 		if (inotify_fd >= 0)
 			close(inotify_fd);
-		close(signal_pipe[READ_END]);
-		close(signal_pipe[WRITE_END]);
 		logging_close();
 		logging_init("udevd-event");
 		setpriority(PRIO_PROCESS, 0, UDEV_PRIORITY);
@@ -520,8 +519,7 @@ static void asmlinkage sig_handler(int signum)
 			break;
 	}
 
-	/* write to pipe, which will wakeup select() in our mainloop */
-	write(signal_pipe[WRITE_END], "", 1);
+	signal_received = 1;
 }
 
 static void udev_done(int pid, int exitstatus)
@@ -633,10 +631,8 @@ static void export_initial_seqnum(struct udev *udev)
 int main(int argc, char *argv[])
 {
 	struct udev *udev;
-	int err;
 	int fd;
 	struct sigaction act;
-	fd_set readfds;
 	const char *value;
 	int daemonize = 0;
 	static const struct option options[] = {
@@ -648,7 +644,6 @@ int main(int argc, char *argv[])
 		{}
 	};
 	int rc = 1;
-	int maxfd;
 
 	udev = udev_new();
 	if (udev == NULL)
@@ -731,34 +726,6 @@ int main(int argc, char *argv[])
 	}
 	udev_monitor_set_receive_buffer_size(kernel_monitor, 128*1024*1024);
 
-	err = pipe(signal_pipe);
-	if (err < 0) {
-		err(udev, "error getting pipes: %m\n");
-		goto exit;
-	}
-
-	err = fcntl(signal_pipe[READ_END], F_GETFL, 0);
-	if (err < 0) {
-		err(udev, "error fcntl on read pipe: %m\n");
-		goto exit;
-	}
-	err = fcntl(signal_pipe[READ_END], F_SETFL, err | O_NONBLOCK);
-	if (err < 0) {
-		err(udev, "error fcntl on read pipe: %m\n");
-		goto exit;
-	}
-
-	err = fcntl(signal_pipe[WRITE_END], F_GETFL, 0);
-	if (err < 0) {
-		err(udev, "error fcntl on write pipe: %m\n");
-		goto exit;
-	}
-	err = fcntl(signal_pipe[WRITE_END], F_SETFL, err | O_NONBLOCK);
-	if (err < 0) {
-		err(udev, "error fcntl on write pipe: %m\n");
-		goto exit;
-	}
-
 	rules = udev_rules_new(udev, 1);
 	if (rules == NULL) {
 		err(udev, "error reading rules\n");
@@ -838,7 +805,6 @@ int main(int argc, char *argv[])
 	memset(&act, 0x00, sizeof(struct sigaction));
 	act.sa_handler = (void (*)(int)) sig_handler;
 	sigemptyset(&act.sa_mask);
-	act.sa_flags = SA_RESTART;
 	sigaction(SIGINT, &act, NULL);
 	sigaction(SIGTERM, &act, NULL);
 	sigaction(SIGCHLD, &act, NULL);
@@ -885,32 +851,45 @@ int main(int argc, char *argv[])
 		max_childs = strtoul(value, NULL, 10);
 	info(udev, "initialize max_childs to %u\n", max_childs);
 
-	maxfd = udev_ctrl_get_fd(udev_ctrl);
-	maxfd = UDEV_MAX(maxfd, udev_monitor_get_fd(kernel_monitor));
-	maxfd = UDEV_MAX(maxfd, signal_pipe[READ_END]);
-	maxfd = UDEV_MAX(maxfd, inotify_fd);
 	while (!udev_exit) {
-		int fdcount;
+		sigset_t blocked_mask, orig_mask;
+		struct pollfd *ctrl_poll, *monitor_poll, *inotify_poll = NULL;
+		struct pollfd pfd[10];
+		int fdcount, nfds = 0;
+
+		sigfillset(&blocked_mask);
+		sigprocmask(SIG_SETMASK, &blocked_mask, &orig_mask);
+		if (signal_received) {
+			sigprocmask(SIG_SETMASK, &orig_mask, NULL);
+			goto handle_signals;
+		}
 
-		FD_ZERO(&readfds);
-		FD_SET(signal_pipe[READ_END], &readfds);
-		FD_SET(udev_ctrl_get_fd(udev_ctrl), &readfds);
-		FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);
+#define POLL_FOR(__desc, __pollptr) do { \
+	pfd[nfds].fd = (__desc); pfd[nfds].events = POLLIN; \
+	__pollptr = &pfd[nfds++]; \
+} while (0)
+		POLL_FOR(udev_ctrl_get_fd(udev_ctrl), ctrl_poll);
+		POLL_FOR(udev_monitor_get_fd(kernel_monitor), monitor_poll);
 		if (inotify_fd >= 0)
-			FD_SET(inotify_fd, &readfds);
-		fdcount = select(maxfd+1, &readfds, NULL, NULL, NULL);
+			POLL_FOR(inotify_fd, inotify_poll);
+#undef POLL_FOR
+
+		fdcount = ppoll(pfd, nfds, NULL, &orig_mask);
+		sigprocmask(SIG_SETMASK, &orig_mask, NULL);
+
 		if (fdcount < 0) {
-			if (errno != EINTR)
-				err(udev, "error in select: %m\n");
+			if (errno == EINTR)
+				goto handle_signals;
+			err(udev, "error in select: %m\n");
 			continue;
 		}
 
 		/* get control message */
-		if (FD_ISSET(udev_ctrl_get_fd(udev_ctrl), &readfds))
+		if (ctrl_poll->revents & POLLIN)
 			handle_ctrl_msg(udev_ctrl);
 
 		/* get kernel uevent */
-		if (FD_ISSET(udev_monitor_get_fd(kernel_monitor), &readfds)) {
+		if (monitor_poll->revents & POLLIN) {
 			struct udev_device *dev;
 
 			dev = udev_monitor_receive_device(kernel_monitor);
@@ -925,15 +904,8 @@ int main(int argc, char *argv[])
 			}
 		}
 
-		/* received a signal, clear our notification pipe */
-		if (FD_ISSET(signal_pipe[READ_END], &readfds)) {
-			char buf[256];
-
-			read(signal_pipe[READ_END], &buf, sizeof(buf));
-		}
-
 		/* rules directory inotify watch */
-		if ((inotify_fd >= 0) && FD_ISSET(inotify_fd, &readfds)) {
+		if (inotify_poll && (inotify_poll->revents & POLLIN)) {
 			int nbytes;
 
 			/* discard all possible events, we can just reload the config */
@@ -952,6 +924,9 @@ int main(int argc, char *argv[])
 			}
 		}
 
+handle_signals:
+		signal_received = 0;
+
 		/* rules changed, set by inotify or a HUP signal */
 		if (reload_config) {
 			struct udev_rules *rules_new;
@@ -979,10 +954,6 @@ int main(int argc, char *argv[])
 	rc = 0;
 exit:
 	udev_rules_unref(rules);
-	if (signal_pipe[READ_END] >= 0)
-		close(signal_pipe[READ_END]);
-	if (signal_pipe[WRITE_END] >= 0)
-		close(signal_pipe[WRITE_END]);
 	udev_ctrl_unref(udev_ctrl);
 	if (inotify_fd >= 0)
 		close(inotify_fd);