mount: use blkid to determine fstype

* Add a function to volume_id that returns an fstype for a
  given device.

* During mount, if the fstype is auto, or blkid disagrees
  with the given fstype, trust blkid's determination of the
  filesystem type and run with it.

Change-Id: I357cbb5d255a30a27152a06de5328b2ef14553f9

include/volume_id.h

@@ -18,6 +18,7 @@
  *	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  */
 
+char *get_fstype_from_devname(const char *device);
 char *get_devname_from_label(const char *spec);
 char *get_devname_from_uuid(const char *spec);
 void display_uuid_cache(int scan_devices);

util-linux/mount.c

@@ -1776,16 +1776,21 @@ static int singlemount(struct mntent *mp, int ignore_busy)
 	int rc = -1;
 	unsigned long vfsflags;
 	char *loopFile = NULL, *filteropts = NULL;
+	char *detected_fstype = NULL;
 	llist_t *fl = NULL;
 	struct stat st;
 
 	errno = 0;
 
 	vfsflags = parse_mount_options(mp->mnt_opts, &filteropts);
 
-	// Treat fstype "auto" as unspecified
-	if (mp->mnt_type && strcmp(mp->mnt_type, "auto") == 0)
-		mp->mnt_type = NULL;
+	detected_fstype = get_fstype_from_devname(mp->mnt_fsname);
+
+	// If fstype is auto or disagrees with blkid, trust blkid's
+	// determination of the filesystem type
+	if ((mp->mnt_type && !strcmp(mp->mnt_type, "auto")) ||
+	    (detected_fstype && strcmp(detected_fstype, mp->mnt_type)))
+		mp->mnt_type = detected_fstype;
 
 	// Might this be a virtual filesystem?
 	if (ENABLE_FEATURE_MOUNT_HELPERS && strchr(mp->mnt_fsname, '#')) {

util-linux/volume_id/get_devname.c

@@ -266,6 +266,26 @@ int add_to_uuid_cache(const char *device)
 	return 0;
 }
 
+char *get_fstype_from_devname(const char *device)
+{
+#if ENABLE_FEATURE_BLKID_TYPE
+	struct uuidCache_s *uc;
+	struct stat *statbuf;
+
+	if (stat(device, statbuf) < 0)
+		return NULL;
+
+	if (!S_ISBLK(statbuf->st_mode) && !S_ISREG(statbuf->st_mode))
+		return NULL;
+
+	add_to_uuid_cache(device);
+	uc = uuidcache_init(0);
+
+	return uc->type;
+#else
+	return NULL;
+#endif
+}
 
 /* Used by mount and findfs */