libmount: allow empty source for mount(2) syscall

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=797438
Signed-off-by: Karel Zak <kzak@redhat.com>

libmount/src/context_mount.c

@@ -451,8 +451,10 @@ static int do_mount(struct libmnt_context *cxt, const char *try_type)
 	src = mnt_fs_get_srcpath(cxt->fs);
 	target = mnt_fs_get_target(cxt->fs);
 
-	if (!src || !target)
+	if (!target)
 		return -EINVAL;
+	if (!src)
+		src = "none";
 
 	type = try_type ? : mnt_fs_get_fstype(cxt->fs);
 

sys-utils/mount.c

@@ -347,7 +347,11 @@ try_readonly:
 			return MOUNT_EX_USAGE;
 		}
 
-		if (src == NULL || tgt == NULL) {
+		/*
+		 * TODO: add mnt_context_fstab_applied() to check if we found
+		 *       target/source in the file.
+		 */
+		if (!tgt) {
 			if (mflags & MS_REMOUNT)
 				warnx(_("%s not mounted"), src ? src : tgt);
 			else