2 files changed, 18 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 93beb865c20d..0072da75221f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1919,6 +1919,17 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
                 printk(KERN_WARNING
                        "EXT4-fs warning: feature flags set on rev 0 fs, "
                        "running e2fsck is recommended\n");
+
+        /*
+         * Since ext4 is still considered development code, we require
+         * that the TEST_FILESYS flag in s->flags be set.
+         */
+        if (!(le32_to_cpu(es->s_flags) & EXT2_FLAGS_TEST_FILESYS)) {
+                printk(KERN_WARNING "EXT4-fs: %s: not marked "
+                       "OK to use with test code.\n", sb->s_id);
+                goto failed_mount;
+        }
+
         /*
          * Check feature flags regardless of the revision level, since we
          * previously didn't change the revision level when setting the flags,
diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
index c4f635a4dd25..250032548597 100644
--- a/include/linux/ext4_fs.h
+++ b/include/linux/ext4_fs.h
@@ -490,6 +490,13 @@ do {									       \
 #define EXT4_ORPHAN_FS                  0x0004  /* Orphans being recovered */
 
 /*
+ * Misc. filesystem flags
+ */
+#define EXT2_FLAGS_SIGNED_HASH          0x0001  /* Signed dirhash in use */
+#define EXT2_FLAGS_UNSIGNED_HASH        0x0002  /* Unsigned dirhash in use */
+#define EXT2_FLAGS_TEST_FILESYS         0x0004  /* to test development code */
+
+/*
  * Mount flags
  */
 #define EXT4_MOUNT_CHECK                0x00001 /* Do mount-time checks */