mount: Add phys_stat_dev_match helper

This helper serves to hide fs specifics (in particular
btrfs) thus the caller won't need the details.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/mount.h

@@ -22,4 +22,6 @@ extern struct mount_info *lookup_mnt_sdev(unsigned int s_dev);
 
 extern struct ns_desc mnt_ns_desc;
 
+extern bool phys_stat_dev_match(dev_t st_dev, dev_t phys_dev);
+
 #endif /* __CR_MOUNT_H__ */

mount.c

@@ -18,6 +18,7 @@
 #include "util-pie.h"
 #include "log.h"
 #include "mount.h"
+#include "mount-btrfs.h"
 #include "pstree.h"
 #include "proc_parse.h"
 #include "image.h"
@@ -97,6 +98,19 @@ struct mount_info *lookup_mnt_sdev(unsigned int s_dev)
 	return NULL;
 }
 
+bool phys_stat_dev_match(dev_t st_dev, dev_t phys_dev)
+{
+	if (st_dev == phys_dev)
+		return true;
+
+	/*
+	 * BTRFS returns subvolume dev-id instead of
+	 * superblock dev-id so we might need additional
+	 * tests here.
+	 */
+	return is_btrfs_subvol(phys_dev, st_dev);
+}
+
 /*
  * Comparer two mounts. Return true if only mount points are differ.
  * Don't care about root and mountpoints, if bind is true.