let lxc-monitor command ask a lxc-monitord instance to quit

doc/lxc-monitor.sgml.in

@@ -50,6 +50,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
     <cmdsynopsis>
       <command>lxc-monitor</command>
       <arg choice="opt">-n <replaceable>name</replaceable></arg>
+      <arg choice="opt">-Q <replaceable>name</replaceable></arg>
     </cmdsynopsis>
   </refsynopsisdiv>
 
@@ -75,6 +76,27 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
   </refsect1>
 
+  <refsect1>
+    <title>Options</title>
+
+    <variablelist>
+      <varlistentry>
+	<term>
+	  <option>-Q, --quit</option>
+	</term>
+	<listitem>
+	  <para>
+	    Ask the lxc-monitord daemon on each given <command>lxcpath</command>
+	    to quit. After receiving this command, lxc-monitord will exit
+	    immediately as soon as it has no clients instead of waiting the
+	    normal 30 seconds for new clients. This is useful if you need to
+	    unmount the filesystem <command>lxcpath</command> is on.
+	  </para>
+	</listitem>
+      </varlistentry>
+     </variablelist>
+  </refsect1>
+
   &commonoptions;
 
   <refsect1>

src/lxc/lxc_monitor.c

@@ -35,7 +35,18 @@
 
 lxc_log_define(lxc_monitor_ui, lxc_monitor);
 
+static bool quit_monitord;
+
+static int my_parser(struct lxc_arguments* args, int c, char* arg)
+{
+	switch (c) {
+	case 'Q': quit_monitord = true; break;
+	}
+	return 0;
+}
+
 static const struct option my_longopts[] = {
+	{"quit", no_argument, 0, 'Q'},
 	LXC_COMMON_OPTIONS
 };
 
@@ -48,10 +59,11 @@ lxc-monitor monitors the state of the NAME container\n\
 \n\
 Options :\n\
   -n, --name=NAME   NAME for name of the container\n\
-                    NAME may be a regular expression",
+                    NAME may be a regular expression\n\
+  -Q, --quit        tell lxc-monitord to quit\n",
 	.name     = ".*",
 	.options  = my_longopts,
-	.parser   = NULL,
+	.parser   = my_parser,
 	.checker  = NULL,
 	.lxcpath_additional = -1,
 };
@@ -74,6 +86,23 @@ int main(int argc, char *argv[])
 			 my_args.progname, my_args.quiet, my_args.lxcpath[0]))
 		return -1;
 
+	if (quit_monitord) {
+		int ret = EXIT_SUCCESS;
+		for (i = 0; i < my_args.lxcpath_cnt; i++) {
+			int fd;
+
+			fd = lxc_monitor_open(my_args.lxcpath[i]);
+			if (fd < 0) {
+				ERROR("Unable to open monitor on path:%s", my_args.lxcpath[i]);
+				ret = EXIT_FAILURE;
+				continue;
+			}
+			write(fd, "quit", 4);
+			close(fd);
+		}
+		return ret;
+	}
+
 	len = strlen(my_args.name) + 3;
 	regexp = malloc(len + 3);
 	if (!regexp) {

src/lxc/lxc_monitord.c

@@ -29,6 +29,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <fcntl.h>
+#include <sys/epoll.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/param.h>
@@ -70,6 +71,7 @@ struct lxc_monitor {
 };
 
 static struct lxc_monitor mon;
+static int quit;
 
 static int lxc_monitord_fifo_create(struct lxc_monitor *mon)
 {
@@ -135,8 +137,18 @@ static int lxc_monitord_sock_handler(int fd, uint32_t events, void *data,
 {
 	struct lxc_monitor *mon = data;
 
-	lxc_monitord_sockfd_remove(mon, fd);
-	return 0;
+	if (events & EPOLLIN) {
+		int rc;
+		char buf[4];
+
+		rc = read(fd, buf, sizeof(buf));
+		if (rc > 0 && !strncmp(buf, "quit", 4))
+			quit = 1;
+	}
+
+	if (events & EPOLLHUP)
+		lxc_monitord_sockfd_remove(mon, fd);
+	return quit;
 }
 
 static int lxc_monitord_sock_accept(int fd, uint32_t events, void *data,
@@ -393,7 +405,7 @@ int main(int argc, char *argv[])
 		ret = lxc_mainloop(&mon.descr, 1000 * 30);
 		if (mon.clientfds_cnt <= 0)
 		{
-			NOTICE("no clients for 30 seconds, exiting");
+			NOTICE("no remaining clients, exiting");
 			break;
 		}
 	}