add c->may_control

This is an api function which will return false if the container
is running, and the caller may not talk to its monitor over its
command socket.  Otherwise - if the container is not running, or
the caller may access it - it returns true.

We can use this in several tools early on to prevent the segvs
etc which we currently get.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

src/lxc/commands.c

@@ -291,6 +291,36 @@ out:
 	return ret;
 }
 
+int lxc_try_cmd(const char *name, const char *lxcpath)
+{
+	int stopped, ret;
+	struct lxc_cmd_rr cmd = {
+		.req = { .cmd = LXC_CMD_GET_INIT_PID },
+	};
+
+	ret = lxc_cmd(name, &cmd, &stopped, lxcpath);
+
+	if (stopped)
+		return 0;
+	if (ret > 0 && cmd.rsp.ret < 0) {
+		errno = cmd.rsp.ret;
+		return -1;
+	}
+	if (ret > 0)
+		return 0;
+
+	/*
+	 * At this point we weren't denied access, and the
+	 * container *was* started.  There was some inexplicable
+	 * error in the protocol.
+	 * I'm not clear on whether we should return -1 here, but
+	 * we didn't receive a -EACCES, so technically it's not that
+	 * we're not allowed to control the container - it's just not
+	 * behaving.
+	 */
+	return 0;
+}
+
 /* Implentations of the commands and their callbacks */
 
 /*

src/lxc/commands.h

@@ -88,5 +88,6 @@ extern int lxc_cmd_init(const char *name, struct lxc_handler *handler,
 			    const char *lxcpath);
 extern int lxc_cmd_mainloop_add(const char *name, struct lxc_epoll_descr *descr,
 				    struct lxc_handler *handler);
+extern int lxc_try_cmd(const char *name, const char *lxcpath);
 
 #endif /* __commands_h */

src/lxc/lxccontainer.c

@@ -2592,6 +2592,11 @@ static bool lxcapi_snapshot_restore(struct lxc_container *c, char *snapname, cha
 	return b;
 }
 
+static bool lxcapi_may_control(struct lxc_container *c)
+{
+	return lxc_try_cmd(c->name, c->config_path) == 0;
+}
+
 static int lxcapi_attach_run_waitl(struct lxc_container *c, lxc_attach_options_t *options, const char *program, const char *arg, ...)
 {
 	va_list ap;
@@ -2711,6 +2716,7 @@ struct lxc_container *lxc_container_new(const char *name, const char *configpath
 	c->snapshot = lxcapi_snapshot;
 	c->snapshot_list = lxcapi_snapshot_list;
 	c->snapshot_restore = lxcapi_snapshot_restore;
+	c->may_control = lxcapi_may_control;
 
 	/* we'll allow the caller to update these later */
 	if (lxc_log_init(NULL, "none", NULL, "lxc_container", 0, c->config_path)) {

src/lxc/lxccontainer.h

@@ -223,6 +223,12 @@ struct lxc_container {
 	 * Returns true on success, false on failure.
 	 */
 	bool (*snapshot_restore)(struct lxc_container *c, char *snapname, char *newname);
+
+	/*
+	 * Return false if there is a control socket for the container monitor,
+	 * and the caller may not access it.  Return true otherwise.
+	 */
+	bool (*may_control)(struct lxc_container *c);
 };
 
 struct lxc_snapshot {

src/tests/Makefile.am

@@ -19,6 +19,7 @@ lxc_usernic_test_SOURCES = ../lxc/lxc_user_nic.c ../lxc/nl.c
 lxc_usernic_test_CFLAGS = -DISTEST
 lxc_test_snapshot_SOURCES = snapshot.c
 lxc_test_concurrent_SOURCES = concurrent.c
+lxc_test_may_control_SOURCES = may_control.c
 
 AM_CFLAGS=-I$(top_srcdir)/src \
 	-DLXCROOTFSMOUNT=\"$(LXCROOTFSMOUNT)\" \
@@ -31,7 +32,7 @@ bin_PROGRAMS = lxc-test-containertests lxc-test-locktests lxc-test-startone \
 	lxc-test-destroytest lxc-test-saveconfig lxc-test-createtest \
 	lxc-test-shutdowntest lxc-test-get_item lxc-test-getkeys lxc-test-lxcpath \
 	lxc-test-cgpath lxc-test-clonetest lxc-test-console lxc-usernic-test \
-	lxc-test-snapshot lxc-test-concurrent
+	lxc-test-snapshot lxc-test-concurrent lxc-test-may-control
 
 bin_SCRIPTS = lxc-test-usernic
 
@@ -53,4 +54,5 @@ EXTRA_DIST = \
 	console.c \
 	lxc-test-usernic \
 	snapshot.c \
-	concurrent.c
+	concurrent.c \
+	may_control.c

src/tests/may_control.c

@@ -0,0 +1,46 @@
+/* control.c
+ *
+ * Copyright © 2013 Canonical, Inc
+ * Author: Serge Hallyn <serge.hallyn@ubuntu.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <lxc/lxccontainer.h>
+
+void usage(char *me)
+{
+	printf("Usage: %s name [lxcpath]\n", me);
+	exit(0);
+}
+
+int main(int argc, char *argv[])
+{
+	char *lxcpath = NULL, *name;
+	bool may = false;
+	struct lxc_container *c;
+
+	if (argc < 2)
+		usage(argv[0]);
+	name = argv[1];
+	if (argc == 3)
+		lxcpath = argv[2];
+	c = lxc_container_new(name, lxcpath);
+	if (c)
+		may = c->may_control(c);
+	printf("You may%s control %s\n", may ? "" : " not", name);
+	exit(may ? 0 : 1);
+}