mnt: add --enable-external-masters option

This option enables external (slave) bind mounts to be resolved.

v2: don't always assume that when the master id matches, the mounts match
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

crtools.c

@@ -206,6 +206,7 @@ int main(int argc, char *argv[], char *envp[])
 		{ "skip-mnt",		required_argument,	0, 1064},
 		{ "enable-fs",		required_argument,	0, 1065},
 		{ "enable-external-sharing", no_argument, 	0, 1066 },
+		{ "enable-external-masters", no_argument, 	0, 1067 },
 		{ },
 	};
 
@@ -430,6 +431,9 @@ int main(int argc, char *argv[], char *envp[])
 		case 1066:
 			opts.enable_external_sharing = true;
 			break;
+		case 1067:
+			opts.enable_external_masters = true;
+			break;
 		case 'M':
 			{
 				char *aux;
@@ -466,6 +470,11 @@ int main(int argc, char *argv[], char *envp[])
 		return 1;
 	}
 
+	if (!opts.autodetect_ext_mounts && (opts.enable_external_masters || opts.enable_external_sharing)) {
+		pr_msg("must specify --ext-mount-map auto with --enable-external-{sharing|masters}");
+		return 1;
+	}
+
 	if (work_dir == NULL)
 		work_dir = imgs_dir;
 
@@ -660,6 +669,8 @@ usage:
 "                        attempt to autodetect external mount mapings\n"
 "  --enable-external-sharing\n"
 "                        allow autoresolving mounts with external sharing\n"
+"  --enable-external-masters\n"
+"                        allow autoresolving mounts with external masters\n"
 "  --manage-cgroups      dump or restore cgroups the process is in\n"
 "  --cgroup-root [controller:]/newroot\n"
 "                        change the root cgroup the controller will be\n"

include/cr_options.h

@@ -64,6 +64,7 @@ struct cr_options {
 	struct list_head	new_cgroup_roots;
 	bool			autodetect_ext_mounts;
 	bool			enable_external_sharing;
+	bool			enable_external_masters;
 	bool			aufs;		/* auto-deteced, not via cli */
 };
 

mount.c

@@ -739,6 +739,20 @@ static int resolve_external_mounts(struct mount_info *info)
 				m->internal_sharing = true;
 		}
 
+		if (m->flags & MS_SLAVE) {
+			if (!opts.enable_external_masters)
+				continue;
+
+			/*
+			 * In order to support something like internal slavery,
+			 * we need to teach can_mount_now and do_mount_one
+			 * about slavery relationships in external mounts. This
+			 * seems like an uncommon case, so we punt for not.
+			 */
+			if (m->master_id != match->shared_id)
+				continue;
+		}
+
 		size = strlen(match->mountpoint + 1) + strlen(m->root) + 1;
 		p = xmalloc(sizeof(char) * size);
 		if (!p)