ext4: Add new "development flag" to the ext4 filesystem

This flag is simply a generic "this is a crash/burn test filesystem"
marker.  If it is set, then filesystem code which is "in development"
will be allowed to mount the filesystem.  Filesystem code which is not
considered ready for prime-time will check for this flag, and if it is
not set, it will refuse to touch the filesystem.

As we start rolling ext4 out to distro's like Fedora, et. al, this makes
it less likely that a user might accidentally start using ext4 on a
production filesystem; a bad thing, since that will essentially make it
be unfsckable until e2fsprogs catches up.

Signed-off-by: Theodore Tso <tytso@MIT.EDU>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>

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 */