Make it possible to share UTS namespace

doc/lxc-start.sgml.in

@@ -217,6 +217,21 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 	</listitem>
       </varlistentry>
 
+      <varlistentry>
+	<term>
+	  <option>--share-uts <replaceable>name|pid</replaceable></option>
+	</term>
+	<listitem>
+	  <para>
+            Inherit a UTS namespace from
+	    a <replaceable>name</replaceable> container or
+	    a <replaceable>pid</replaceable>. The starting LXC will
+	    not set the hostname, but the container OS may do it
+	    anyway.
+	  </para>
+	</listitem>
+      </varlistentry>
+
     </variablelist>
 
   </refsect1>

src/lxc/conf.c

@@ -3141,9 +3141,11 @@ int ttys_shift_ids(struct lxc_conf *c)
 
 int lxc_setup(const char *name, struct lxc_conf *lxc_conf, const char *lxcpath, struct cgroup_process_info *cgroup_info)
 {
-	if (setup_utsname(lxc_conf->utsname)) {
-		ERROR("failed to setup the utsname for '%s'", name);
-		return -1;
+	if (lxc_conf->inherit_ns_fd[LXC_NS_UTS] == -1) {
+		if (setup_utsname(lxc_conf->utsname)) {
+			ERROR("failed to setup the utsname for '%s'", name);
+			return -1;
+		}
 	}
 
 	if (setup_network(&lxc_conf->network)) {

src/lxc/lxc_start.c

@@ -53,6 +53,7 @@
 
 #define OPT_SHARE_NET OPT_USAGE+1
 #define OPT_SHARE_IPC OPT_USAGE+2
+#define OPT_SHARE_UTS OPT_USAGE+3
 
 lxc_log_define(lxc_start_ui, lxc_start);
 
@@ -153,6 +154,7 @@ static int my_parser(struct lxc_arguments* args, int c, char* arg)
 	case 'p': args->pidfile = arg; break;
 	case OPT_SHARE_NET: args->share_ns[LXC_NS_NET] = arg; break;
 	case OPT_SHARE_IPC: args->share_ns[LXC_NS_IPC] = arg; break;
+	case OPT_SHARE_UTS: args->share_ns[LXC_NS_UTS] = arg; break;
 	}
 	return 0;
 }
@@ -167,6 +169,7 @@ static const struct option my_longopts[] = {
 	{"pidfile", required_argument, 0, 'p'},
 	{"share-net", required_argument, 0, OPT_SHARE_NET},
 	{"share-ipc", required_argument, 0, OPT_SHARE_IPC},
+	{"share-uts", required_argument, 0, OPT_SHARE_UTS},
 	LXC_COMMON_OPTIONS
 };
 
@@ -190,6 +193,7 @@ Options :\n\
   -s, --define KEY=VAL   Assign VAL to configuration variable KEY\n\
       --share-net=NAME   Share a network namespace with another container or pid\n\
       --share-ipc=NAME   Share an IPC namespace with another container or pid\n\
+      --share-uts=NAME   Share a UTS namespace with another container or pid\n\
 ",
 	.options   = my_longopts,
 	.parser    = my_parser,

src/lxc/start.c

@@ -721,13 +721,13 @@ int lxc_spawn(struct lxc_handler *handler)
 	int preserve_mask = 0, i;
 
 	for (i = 0; i < LXC_NS_MAX; i++)
-		if (handler->conf->inherit_ns_fd[i] > -1)
+		if (handler->conf->inherit_ns_fd[i] != -1)
 			preserve_mask |= ns_info[i].clone_flag;
 
 	if (lxc_sync_init(handler))
 		return -1;
 
-	handler->clone_flags = CLONE_NEWUTS|CLONE_NEWPID|CLONE_NEWNS;
+	handler->clone_flags = CLONE_NEWPID|CLONE_NEWNS;
 	if (!lxc_list_empty(&handler->conf->id_map)) {
 		INFO("Cloning a new user namespace");
 		handler->clone_flags |= CLONE_NEWUSER;
@@ -772,6 +772,12 @@ int lxc_spawn(struct lxc_handler *handler)
 		INFO("Inheriting an IPC namespace");
 	}
 
+	if (handler->conf->inherit_ns_fd[LXC_NS_UTS] == -1) {
+		handler->clone_flags |= CLONE_NEWUTS;
+	} else {
+		INFO("Inheriting a UTS namespace");
+	}
+
 
 	cgroup_meta = lxc_cgroup_load_meta();
 	if (!cgroup_meta) {