error checking in signals.c + Add signals to documentation

2 files changed, 27 insertions, 5 deletions

diff --git a/man/feh.1 b/man/feh.1
index aef10a7..e408e92 100644
--- a/man/feh.1
+++ b/man/feh.1
@@ -677,6 +677,17 @@ the mouse.  The zoom will always happen so that the pixel on which you entered
 the zoom mode remains stationary.  So, to enlarge a specific part of an image,
 click the zoom button on that part.
 .
+.Sh SIGNALS
+In slideshow mode,
+.Nm
+handles the following signals:
+.Bl -tag -width indent
+.It SIGUSR1
+Switch to next image
+.It SIGUSR2
+Switch to previous image
+.El
+.
 .Sh USAGE EXAMPLES
 Here are some examples of useful option combinations
 .Bl -tag -width indent
diff --git a/src/signals.c b/src/signals.c
index 4e51c77..eca77e6 100644
--- a/src/signals.c
+++ b/src/signals.c
@@ -34,15 +34,26 @@ void setup_signal_handlers()
 	sigset_t feh_ss;
 	D_ENTER(4);
 
-	sigemptyset(&feh_ss);
-	sigaddset(&feh_ss, SIGUSR1);
-	sigaddset(&feh_ss, SIGUSR2);
+	if (
+		(sigemptyset(&feh_ss) == -1) ||
+		(sigaddset(&feh_ss, SIGUSR1) == -1) ||
+		(sigaddset(&feh_ss, SIGUSR2) == -1))
+	{
+		weprintf("Failed to set up signal mask, SIGUSR1/2 won't work");
+		D_RETURN_(4);
+	}
 
 	feh_sh.sa_handler = feh_handle_signal;
 	feh_sh.sa_mask = feh_ss;
 
-	sigaction(SIGUSR1, &feh_sh, NULL);
-	sigaction(SIGUSR2, &feh_sh, NULL);
+	if (
+		(sigaction(SIGUSR1, &feh_sh, NULL) == -1) ||
+		(sigaction(SIGUSR2, &feh_sh, NULL) == -1))
+	{
+		weprintf("Failed to set up signal handler, SIGUSR1/2 won't work");
+		D_RETURN_(4);
+	}
+
 	D_RETURN_(4);
 }