mnt: relax constraints on fuse mounts

1. If a fuse connection is present, but there are no fuse mounts of that type
   in the mount namespace, don't refuse to dump.
2. If there are mounts of that type in the container but they are external,
   we're going to bind them anyway, so there's no fuse-specific things that
   need to be done, so it is safe to dump.

v2: check that the fstype is fuse as well
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -1024,6 +1024,47 @@ out:
 	return ret;
 }
 
+static int fusectl_dump(struct mount_info *pm)
+{
+	int fd, ret = -1;
+	struct dirent *de;
+	DIR *fdir = NULL;
+
+	fd = open_mountpoint(pm);
+	if (fd < 0)
+		return -1;
+
+	fdir = fdopendir(fd);
+	if (fdir == NULL) {
+		close(fd);
+		return -1;
+	}
+
+	while ((de = readdir(fdir))) {
+		int id;
+		struct mount_info *it;
+
+		if (dir_dots(de))
+			continue;
+
+		if (sscanf(de->d_name, "%d", &id) != 1) {
+			pr_err("wrong number of items scanned in fusectl dump\n");
+			goto out;
+		}
+
+		for (it = mntinfo; it; it = it->next) {
+			if (it->fstype->code == FSTYPE__FUSE && id == minor(it->s_dev) && !it->external) {
+				pr_err("%s is a fuse mount but not external\n", it->mountpoint);
+				goto out;
+			}
+		}
+	}
+
+	ret = 0;
+out:
+	closedir(fdir);
+	return ret;
+}
 
 static int dump_empty_fs(struct mount_info *pm)
 {
@@ -1055,6 +1096,15 @@ out:
 	return ret;
 }
 
+/*
+ * Some fses (fuse) cannot be dumped, so we should always fail on dump/restore
+ * of these fses.
+ */
+static int always_fail(struct mount_info *pm)
+{
+	return -1;
+}
+
 static struct fstype fstypes[] = {
 	{
 		.name = "unsupported",
@@ -1102,7 +1152,7 @@ static struct fstype fstypes[] = {
 		.code = FSTYPE__SECURITYFS,
 	}, {
 		.name = "fusectl",
-		.dump = dump_empty_fs,
+		.dump = fusectl_dump,
 		.code = FSTYPE__FUSECTL,
 	}, {
 		.name = "debugfs",
@@ -1114,6 +1164,11 @@ static struct fstype fstypes[] = {
 		.name = "aufs",
 		.code = FSTYPE__AUFS,
 		.parse = aufs_parse,
+	}, {
+		.name = "fuse",
+		.code = FSTYPE__FUSE,
+		.dump = always_fail,
+		.restore = always_fail,
 	},
 };
 

protobuf/mnt.proto

@@ -16,6 +16,7 @@ enum fstype {
 	CGROUP			= 12;
 	AUFS			= 13;
 	MQUEUE			= 14;
+	FUSE			= 15;
 };
 
 message mnt_entry {