mnt: add --enable-external-sharing flag

With this flag, external shared bind mounts are attempted to be resolved
automatically.

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

crtools.c

@@ -205,6 +205,7 @@ int main(int argc, char *argv[], char *envp[])
 		{ "feature",		required_argument,	0, 1063	},
 		{ "skip-mnt",		required_argument,	0, 1064},
 		{ "enable-fs",		required_argument,	0, 1065},
+		{ "enable-external-sharing", no_argument, 	0, 1066 },
 		{ },
 	};
 
@@ -426,6 +427,9 @@ int main(int argc, char *argv[], char *envp[])
 			if (!add_fsname_auto(optarg))
 				return 1;
 			break;
+		case 1066:
+			opts.enable_external_sharing = true;
+			break;
 		case 'M':
 			{
 				char *aux;
@@ -654,6 +658,8 @@ usage:
 "                        add external mount mapping\n"
 "  -M|--ext-mount-map auto\n"
 "                        attempt to autodetect external mount mapings\n"
+"  --enable-external-sharing\n"
+"                        allow autoresolving mounts with external sharing\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

@@ -63,6 +63,7 @@ struct cr_options {
 	char			*new_global_cg_root;
 	struct list_head	new_cgroup_roots;
 	bool			autodetect_ext_mounts;
+	bool			enable_external_sharing;
 	bool			aufs;		/* auto-deteced, not via cli */
 };
 

include/proc_parse.h

@@ -130,6 +130,7 @@ struct mount_info {
 	struct ns_id	*nsid;
 
 	struct ext_mount *external;
+	bool		internal_sharing;
 
 	/* tree linkage */
 	struct mount_info *parent;

mount.c

@@ -731,6 +731,14 @@ static int resolve_external_mounts(struct mount_info *info)
 		if (!match)
 			continue;
 
+		if (m->flags & MS_SHARED) {
+			if (!opts.enable_external_sharing)
+				continue;
+
+			if (m->shared_id != match->shared_id)
+				m->internal_sharing = true;
+		}
+
 		size = strlen(match->mountpoint + 1) + strlen(m->root) + 1;
 		p = xmalloc(sizeof(char) * size);
 		if (!p)
@@ -1437,6 +1445,11 @@ static int dump_one_mountpoint(struct mount_info *pm, struct cr_img *img)
 		me.with_plugin = true;
 	}
 
+	if (pm->internal_sharing) {
+		me.has_internal_sharing = true;
+		me.internal_sharing = true;
+	}
+
 	if (pm->external) {
 		/*
 		 * For external mount points dump the mapping's
@@ -1778,6 +1791,7 @@ static int restore_ext_mount(struct mount_info *mi)
 static int do_bind_mount(struct mount_info *mi)
 {
 	bool shared = 0;
+	bool force_private_remount = false;
 
 	if (!mi->need_plugin) {
 		char *root, rpath[PATH_MAX];
@@ -1791,6 +1805,7 @@ static int do_bind_mount(struct mount_info *mi)
 			 * to proper location in the namespace we restore.
 			 */
 			root = mi->root;
+			force_private_remount = mi->internal_sharing;
 			goto do_bind;
 		}
 
@@ -1827,7 +1842,7 @@ do_bind:
 	 * shared - the mount is in the same shared group with mi->bind
 	 * mi->shared_id && !shared - create a new shared group
 	 */
-	if (restore_shared_options(mi, !shared && !mi->master_id,
+	if (restore_shared_options(mi, force_private_remount || (!shared && !mi->master_id),
 					mi->shared_id && !shared,
 					mi->master_id))
 		return -1;
@@ -2139,6 +2154,9 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
 		if (!pm->source)
 			goto err;
 
+		if (me->has_internal_sharing)
+			pm->internal_sharing = me->internal_sharing;
+
 		/* FIXME: abort unsupported early */
 		pm->fstype		= decode_fstype(me->fstype, me->fsname);
 

protobuf/mnt.proto

@@ -39,4 +39,5 @@ message mnt_entry {
 	optional bool		ext_mount		= 13;
 
 	optional string		fsname			= 14;
+	optional bool		internal_sharing	= 15;
 }