simplify post-lock cmd and die if it fails

this patch does two things:

0. simplify the code by using posix_spawn()
1. unify the behavior of what happens if the post-lock cmd fails.

currently, if `fork()` fails, slock will die without locking the screen.
HOWEVER if `execvp()` fails it prints a message to stderr (which the
user cannot see since the screen has been locked already) and only exits
the child while the parent locks the screen.

to reproduce:

	# slock some_bin_that_doesnt_exist

this behavior is inconsistent, if the idea is that post-lock cmd is
_not_ important then we shouldn't `die()` on `fork()` failure either.
and if we assume that the post-lock cmd _is_ important, then we should
die on exec failure as well.

this patch assumes the latter and calls `die()` if `posix_spawn()`
fails.

1 files changed, 7 insertions, 9 deletions

diff --git a/slock.c b/slock.c
index b2f14e3..b5a9b04 100644
--- a/slock.c
+++ b/slock.c
@@ -13,6 +13,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <spawn.h>
 #include <sys/types.h>
 #include <X11/extensions/Xrandr.h>
 #include <X11/keysym.h>
@@ -376,15 +377,12 @@ main(int argc, char **argv) {
 
 	/* run post-lock command */
 	if (argc > 0) {
-		switch (fork()) {
-		case -1:
-			die("slock: fork failed: %s\n", strerror(errno));
-		case 0:
-			if (close(ConnectionNumber(dpy)) < 0)
-				die("slock: close: %s\n", strerror(errno));
-			execvp(argv[0], argv);
-			fprintf(stderr, "slock: execvp %s: %s\n", argv[0], strerror(errno));
-			_exit(1);
+		pid_t pid;
+		extern char **environ;
+		int err = posix_spawnp(&pid, argv[0], NULL, NULL, argv, environ);
+		if (err) {
+			die("slock: failed to execute post-lock command: %s: %s\n",
+			    argv[0], strerror(err));
 		}
 	}