openrc-shutdown: broadcast: simplify non-blocking logic

Get rid of the setjmp/longjmp and just handle EINTR. This avoids messing
with the stack and simplifies program flow.

Bug: https://bugs.gentoo.org/923326
Signed-off-by: Mike Gilbert <[email protected]>

src/openrc-shutdown/broadcast.c

@@ -14,11 +14,11 @@
  */
 
 
+#include <errno.h>
 #include <fcntl.h>
 #include <paths.h>
 #include <pwd.h>
 #include <signal.h>
-#include <setjmp.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -37,14 +37,12 @@
 # define _PATH_DEV	"/dev/"
 #endif
 
-static sigjmp_buf jbuf;
-
 /*
  *	Alarm handler
  */
-RC_NORETURN static void handler(int arg RC_UNUSED)
+static void handler(int arg RC_UNUSED)
 {
-	siglongjmp(jbuf, 1);
+	/* do nothing */
 }
 
 static void getuidtty(char **userp, char **ttyp)
@@ -124,15 +122,11 @@ void broadcast(char *text)
 	char *p;
 	char *line = NULL;
 	struct sigaction sa;
+	int fd;
+	FILE *tp;
 	int	flags;
 	char *term = NULL;
 	struct utmpx *utmp;
-	/*
-	 * These are set across the sigsetjmp call, so they can't be stored on
-	 * the stack, otherwise they might be clobbered.
-	 */
-	static int fd;
-	static FILE *tp;
 
 	getuidtty(&user, &tty);
 
@@ -159,6 +153,7 @@ void broadcast(char *text)
 	if (fork() != 0)
 		return;
 
+	/* Set up a noop signal handler to generate EINTR */
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = handler;
 	sigemptyset(&sa.sa_mask);
@@ -179,24 +174,23 @@ void broadcast(char *text)
 		}
 
 		/*
-		 *	Open it non-delay
+		 * Open it non-delay
+		 * Set an alarm to generate EINTR in case we block.
 		 */
-		if (sigsetjmp(jbuf, 1) == 0) {
-			alarm(2);
-			flags = O_WRONLY|O_NDELAY|O_NOCTTY;
-			if (file_isatty(term) && (fd = open(term, flags)) >= 0) {
-				if (isatty(fd) && (tp = fdopen(fd, "w")) != NULL) {
-					fputs(line, tp);
-					fputs(text, tp);
-					fflush(tp);
-				}
+		alarm(2);
+		flags = O_WRONLY|O_NDELAY|O_NOCTTY;
+		if (file_isatty(term) && (fd = open(term, flags)) >= 0) {
+			if (isatty(fd) && (tp = fdopen(fd, "w")) != NULL) {
+				if ((fputs(line, tp) == EOF || fputs(text, tp) == EOF)
+				   && errno == EINTR)
+					/* Set another alarm for fclose */
+					alarm(1);
+				fclose(tp);
 			}
+			else
+				close(fd);
 		}
 		alarm(0);
-		if (fd >= 0)
-			close(fd);
-		if (tp != NULL)
-			fclose(tp);
 		free(term);
 	}
 	endutxent();