Allow specifying a container by name or pid in --share-net option.

src/lxc/lxc_start.c

@@ -93,6 +93,48 @@ err:
 	return err;
 }
 
+static int pid_from_lxcname(const char *lxcname_or_pid, const char *lxcpath) {
+	char *eptr;
+	int pid = strtol(lxcname_or_pid, &eptr, 10);
+	if (*eptr != '\0' || pid < 1) {
+		struct lxc_container *s;
+		s = lxc_container_new(lxcname_or_pid, lxcpath);
+		if (!s) {
+			SYSERROR("'%s' is not a valid pid nor a container name", lxcname_or_pid);
+			return -1;
+		}
+
+		if (!s->may_control(s)) {
+			SYSERROR("Insufficient privileges to control container '%s'", s->name);
+			return -1;
+		}
+
+		pid = s->init_pid(s);
+		if (pid < 1) {
+			SYSERROR("Is container '%s' running?", s->name);
+			return -1;
+		}
+	}
+	if (kill(pid, 0) < 0) {
+		SYSERROR("Can't send signal to pid %d", pid);
+		return -1;
+	}
+	return pid;
+}
+
+static int open_ns(int pid, const char *ns_proc_name) {
+	int fd;
+	char path[MAXPATHLEN];
+	snprintf(path, MAXPATHLEN, "/proc/%d/ns/net", pid);
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0) {
+		SYSERROR("failed to open %s", path);
+		return -1;
+	}
+	return fd;
+}
+
 static int my_parser(struct lxc_arguments* args, int c, char* arg)
 {
 	switch (c) {
@@ -138,7 +180,7 @@ Options :\n\
                          If not specified, exit with failure instead\n\
 		         Note: --daemon implies --close-all-fds\n\
   -s, --define KEY=VAL   Assign VAL to configuration variable KEY\n\
-      --share-net=PID    Share a network namespace with another container\n\
+      --share-net=NAME   Share a network namespace with another container or pid\n\
 ",
 	.options   = my_longopts,
 	.parser    = my_parser,
@@ -256,23 +298,14 @@ int main(int argc, char *argv[])
 	}
 
 	if (my_args.share_net != NULL) {
-		char *eptr;
 		int fd;
-		int pid = strtol(my_args.share_net, &eptr, 10);
-		if (*eptr != '\0') {
-			SYSERROR("'%s' is not a valid pid number", my_args.share_net);
-			goto out;
-		}
-		char path[MAXPATHLEN];
-		int ret = snprintf(path, MAXPATHLEN, "/proc/%d/ns/net", pid);
-		if (ret < 0 || ret >= MAXPATHLEN)
+		int pid = pid_from_lxcname(my_args.share_net, lxcpath);
+		if (pid < 1)
 			goto out;
 
-		fd = open(path, O_RDONLY);
-		if (fd < 0) {
-			SYSERROR("failed to open %s", path);
+		fd = open_ns(pid, "net");
+		if (fd < 0)
 			goto out;
-		}
 		conf->inherit_ns_fd[LXC_NS_NET] = fd;
 	}