pping: Reopen output file on SIGHUP

Make the user space process reopen the output file (if used with the
-w/--write option) when it recieves a SIGHUP signal. This makes it
possible to for example rotate the output files with logrotate.

In case the program receives the SIGHUP signal is BEFORE the output
file has been moved, the program will throw a warning and then
continue writing to its current file handle until another SIGHUP
signal is received.

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>

Author: simosund

pping/pping.c

@@ -1451,7 +1451,6 @@ static int report_aggregated_rtt_map(struct output_context *out_ctx, int map_fd,
 	return err;
 }
 
-
 static int report_aggregated_rtts(struct output_context *out_ctx,
 				  struct aggregation_maps *maps,
 				  struct aggregation_config *agg_conf)
@@ -1710,6 +1709,26 @@ static int close_output(struct output_context *out_ctx)
 	return err;
 }
 
+/* Will try to reopen *out_ctx
+ * If it is able to open the new output it will return 0, replace *out_ctx with
+ * the new output and close the old output_context. If it fails at opening a
+ * new output_context it will return a negative error code and *out_ctx will
+ * remain unchanged */
+static int reopen_output(struct output_context **out_ctx, const char *filename,
+			 struct aggregation_config *agg_conf)
+{
+	struct output_context *new_out;
+
+	new_out = open_output(filename, (*out_ctx)->format, agg_conf);
+	if (!new_out)
+		return -errno;
+
+	close_output(*out_ctx);
+
+	*out_ctx = new_out;
+	return 0;
+}
+
 static int init_signalfd(void)
 {
 	sigset_t mask;
@@ -1718,6 +1737,7 @@ static int init_signalfd(void)
 	sigemptyset(&mask);
 	sigaddset(&mask, SIGINT);
 	sigaddset(&mask, SIGTERM);
+	sigaddset(&mask, SIGHUP);
 
 	fd = signalfd(-1, &mask, 0);
 	if (fd < 0)
@@ -1733,25 +1753,38 @@ static int init_signalfd(void)
 	return fd;
 }
 
-/* Returns PPING_ABORT to indicate the program should be halted or a negative
- * error code */
-static int handle_signalfd(int sigfd)
+/* Returns 0 if signal was successfully handled, PPING_ABORT if signal
+ * indicates program should be halted or a negative error code on failure. */
+static int handle_signalfd(int sigfd, struct output_context **out_ctx,
+			   const char *filename,
+			   struct aggregation_config *agg_conf)
 {
 	struct signalfd_siginfo siginfo;
-	int ret;
+	int ret, err;
 
 	ret = read(sigfd, &siginfo, sizeof(siginfo));
 	if (ret != sizeof(siginfo)) {
 		fprintf(stderr, "Failed reading signalfd\n");
 		return -EBADFD;
 	}
 
-	if (siginfo.ssi_signo == SIGINT || siginfo.ssi_signo == SIGTERM) {
+	if (siginfo.ssi_signo == SIGHUP) {
+		if (filename) {
+			err = reopen_output(out_ctx, filename, agg_conf);
+			if (err)
+				fprintf(stderr,
+					"Warning: failed reopening %s: %s\n",
+					filename, get_libbpf_strerror(err));
+		} // If not writing to file, simply ignore the SIGHUP
+	} else if (siginfo.ssi_signo == SIGINT ||
+		   siginfo.ssi_signo == SIGTERM) {
 		return PPING_ABORT;
 	} else {
 		fprintf(stderr, "Unexpected signal %d\n", siginfo.ssi_signo);
 		return -EBADMSG;
 	}
+
+	return 0;
 }
 
 static int init_perfbuffer(struct bpf_object *obj, struct pping_config *config,
@@ -2050,8 +2083,13 @@ static int epoll_poll_events(int epfd, struct pping_config *config,
 				&config->agg_conf);
 			break;
 		case PPING_EPEVENT_TYPE_SIGNAL:
-			err = handle_signalfd(events[i].data.u64 &
-					      PPING_EPEVENT_MASK);
+			err = handle_signalfd(
+				events[i].data.u64 & PPING_EPEVENT_MASK,
+				&config->out_ctx,
+				config->write_to_file ? config->filename : NULL,
+				config->bpf_config.agg_rtts ?
+					&config->agg_conf :
+					NULL);
 			break;
 		case PPING_EPEVENT_TYPE_PIPE:
 			err = handle_pipefd(events[i].data.u64 &
@@ -2156,7 +2194,7 @@ int main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
-	// Setup signalhandling (allow graceful shutdown on SIGINT/SIGTERM)
+	// Setup signalhandling (allow graceful shutdown on SIGINT/SIGTERM, reopen on SIGHUP)
 	sigfd = init_signalfd();
 	if (sigfd < 0) {
 		fprintf(stderr, "Failed creating signalfd: %s\n",