fs/ext2: Ignore the large_dir incompat feature

Recently, ext4 added the large_dir feature, which adds support for
a 3 level htree directory support.

The GRUB supports existing file systems with htree directories by
ignoring their existence, and since the index nodes for the hash tree
look like deleted directory entries (by design), the GRUB can simply do
a brute force O(n) linear search of directories. The same is true for
3 level deep htrees indicated by large_dir feature flag.

Hence, it is safe for the GRUB to ignore the large_dir incompat feature.

Fixes: https://savannah.gnu.org/bugs/?61606
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/fs/ext2.c b/grub-core/fs/ext2.c
index 0989e26e16b3dc7aa46e38eab28b131c31371e76..e1cc5e62aa31ddd2fab84caa078853a7e3e6201d 100644 (file)
--- a/grub-core/fs/ext2.c
+++ b/grub-core/fs/ext2.c
@@ -104,6 +104,7 @@ GRUB_MOD_LICENSE ("GPLv3+");
 #define EXT4_FEATURE_INCOMPAT_MMP              0x0100
 #define EXT4_FEATURE_INCOMPAT_FLEX_BG          0x0200
 #define EXT4_FEATURE_INCOMPAT_CSUM_SEED                0x2000
+#define EXT4_FEATURE_INCOMPAT_LARGEDIR         0x4000 /* >2GB or 3 level htree */
 #define EXT4_FEATURE_INCOMPAT_ENCRYPT          0x10000
 
 /* The set of back-incompatible features this driver DOES support. Add (OR)
@@ -129,10 +130,17 @@ GRUB_MOD_LICENSE ("GPLv3+");
  *                 checksummed filesystem. Safe to ignore for now since the
  *                 driver doesn't support checksum verification. However, it
  *                 has to be removed from this list if the support is added later.
+ * large_dir:      Not back-incompatible given that the GRUB ext2 driver does
+ *                 not implement EXT2_FEATURE_COMPAT_DIR_INDEX. If the GRUB
+ *                 eventually supports the htree feature (aka dir_index)
+ *                 it should support 3 level htrees and then move
+ *                 EXT4_FEATURE_INCOMPAT_LARGEDIR to
+ *                 EXT2_DRIVER_SUPPORTED_INCOMPAT.
  */
 #define EXT2_DRIVER_IGNORED_INCOMPAT ( EXT3_FEATURE_INCOMPAT_RECOVER \
                                     | EXT4_FEATURE_INCOMPAT_MMP \
-                                    | EXT4_FEATURE_INCOMPAT_CSUM_SEED)
+                                    | EXT4_FEATURE_INCOMPAT_CSUM_SEED \
+                                    | EXT4_FEATURE_INCOMPAT_LARGEDIR)
 
 #define EXT3_JOURNAL_MAGIC_NUMBER      0xc03b3998U