ext4: check for ext[23] file system features when mounting as ext[23]

Provide better emulation for ext[23] mode by enforcing that the file
system does not have any unsupported file system features as defined
by ext[23] when emulating the ext[23] file system driver when
CONFIG_EXT4_USE_FOR_EXT23 is defined.

This causes the file system type information in /proc/mounts to be
correct for the automatically mounted root file system.  This also
means that "mount -t ext2 /dev/sda /mnt" will fail if /dev/sda
contains an ext3 or ext4 file system, just as one would expect if the
original ext2 file system driver were in use.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4daaf2b753f4..076c5d212a3c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1351,6 +1351,21 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 #define EXT4_FEATURE_INCOMPAT_EA_INODE          0x0400 /* EA in inode */
 #define EXT4_FEATURE_INCOMPAT_DIRDATA           0x1000 /* data in dirent */
 
+#define EXT2_FEATURE_COMPAT_SUPP        EXT4_FEATURE_COMPAT_EXT_ATTR
+#define EXT2_FEATURE_INCOMPAT_SUPP      (EXT4_FEATURE_INCOMPAT_FILETYPE| \
+                                         EXT4_FEATURE_INCOMPAT_META_BG)
+#define EXT2_FEATURE_RO_COMPAT_SUPP     (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
+                                         EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+                                         EXT4_FEATURE_RO_COMPAT_BTREE_DIR)
+
+#define EXT3_FEATURE_COMPAT_SUPP        EXT4_FEATURE_COMPAT_EXT_ATTR
+#define EXT3_FEATURE_INCOMPAT_SUPP      (EXT4_FEATURE_INCOMPAT_FILETYPE| \
+                                         EXT4_FEATURE_INCOMPAT_RECOVER| \
+                                         EXT4_FEATURE_INCOMPAT_META_BG)
+#define EXT3_FEATURE_RO_COMPAT_SUPP     (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
+                                         EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+                                         EXT4_FEATURE_RO_COMPAT_BTREE_DIR)
+
 #define EXT4_FEATURE_COMPAT_SUPP        EXT2_FEATURE_COMPAT_EXT_ATTR
 #define EXT4_FEATURE_INCOMPAT_SUPP      (EXT4_FEATURE_INCOMPAT_FILETYPE| \
                                          EXT4_FEATURE_INCOMPAT_RECOVER| \