procd: show process's exit code

Adds feature to show exit code of processes launched by procd.
The exit code is shown for finished process when ubus's
service list method is called.

The exit code value is computed according to waitpid(2)
and http://tldp.org/LDP/abs/html/exitcodes.html

Signed-off-by: Ondřej Votava <ondrej.votava@cvut.cz>

service/instance.c

@@ -566,6 +566,24 @@ instance_delete(struct service_instance *in)
 	service_stopped(s);
 }
 
+static int
+instance_exit_code(int ret)
+{
+	if (WIFEXITED(ret)) {
+		return WEXITSTATUS(ret);
+	}
+
+	if (WIFSIGNALED(ret)) {
+		return SIGNALLED_OFFSET + WTERMSIG(ret);
+	}
+
+	if (WIFSTOPPED(ret)) {
+		return WSTOPSIG(ret);
+	}
+
+	return 1;
+}
+
 static void
 instance_exit(struct uloop_process *p, int ret)
 {
@@ -580,6 +598,7 @@ instance_exit(struct uloop_process *p, int ret)
 
 	DEBUG(2, "Instance %s::%s exit with error code %d after %ld seconds\n", in->srv->name, in->name, ret, runtime);
 
+	in->exit_code = instance_exit_code(ret);
 	uloop_timeout_cancel(&in->timeout);
 	service_event("instance.stop", in->srv->name, in->name);
 
@@ -1126,6 +1145,7 @@ instance_init(struct service_instance *in, struct service *s, struct blob_attr *
 	in->proc.cb = instance_exit;
 	in->term_timeout = 5;
 	in->syslog_facility = LOG_DAEMON;
+	in->exit_code = 0;
 
 	in->_stdout.fd.fd = -2;
 	in->_stdout.stream.string_data = true;
@@ -1159,6 +1179,8 @@ void instance_dump(struct blob_buf *b, struct service_instance *in, int verbose)
 	if (in->command)
 		blobmsg_add_blob(b, in->command);
 	blobmsg_add_u32(b, "term_timeout", in->term_timeout);
+	if (!in->proc.pending)
+		blobmsg_add_u32(b, "exit_code", in->exit_code);
 
 	if (!avl_is_empty(&in->errors.avl)) {
 		struct blobmsg_list_node *var;

service/instance.h

@@ -21,6 +21,7 @@
 #include "../utils/utils.h"
 
 #define RESPAWN_ERROR	(5 * 60)
+#define SIGNALLED_OFFSET 128
 
 struct jail {
 	bool procfs;
@@ -63,6 +64,7 @@ struct service_instance {
 	char *seccomp;
 	char *pidfile;
 	int syslog_facility;
+	int exit_code;
 
 	uint32_t term_timeout;
 	uint32_t respawn_timeout;