ext4: don't update s_rev_level if not required

Don't update the superblock s_rev_level during mount if it isn't
actually necessary, only if superblock features are being set by
the kernel.  This was originally added for ext3 since it always
set the INCOMPAT_RECOVER and HAS_JOURNAL features during mount,
but this is not needed since no journal mode was added to ext4.

That will allow Geert to mount his 20-year-old ext2 rev 0.0 m68k
filesystem, as a testament of the backward compatibility of ext4.

Fixes: 0390131b ("ext4: Allow ext4 to run without a journal")
Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1665,6 +1665,8 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 #define EXT4_FEATURE_INCOMPAT_INLINE_DATA	0x8000 /* data in inode */
 #define EXT4_FEATURE_INCOMPAT_ENCRYPT		0x10000
 
+extern void ext4_update_dynamic_rev(struct super_block *sb);
+
 #define EXT4_FEATURE_COMPAT_FUNCS(name, flagname) \
 static inline bool ext4_has_feature_##name(struct super_block *sb) \
 { \
@@ -1673,6 +1675,7 @@ static inline bool ext4_has_feature_##name(struct super_block *sb) \
 } \
 static inline void ext4_set_feature_##name(struct super_block *sb) \
 { \
+	ext4_update_dynamic_rev(sb); \
 	EXT4_SB(sb)->s_es->s_feature_compat |= \
 		cpu_to_le32(EXT4_FEATURE_COMPAT_##flagname); \
 } \
@@ -1690,6 +1693,7 @@ static inline bool ext4_has_feature_##name(struct super_block *sb) \
 } \
 static inline void ext4_set_feature_##name(struct super_block *sb) \
 { \
+	ext4_update_dynamic_rev(sb); \
 	EXT4_SB(sb)->s_es->s_feature_ro_compat |= \
 		cpu_to_le32(EXT4_FEATURE_RO_COMPAT_##flagname); \
 } \
@@ -1707,6 +1711,7 @@ static inline bool ext4_has_feature_##name(struct super_block *sb) \
 } \
 static inline void ext4_set_feature_##name(struct super_block *sb) \
 { \
+	ext4_update_dynamic_rev(sb); \
 	EXT4_SB(sb)->s_es->s_feature_incompat |= \
 		cpu_to_le32(EXT4_FEATURE_INCOMPAT_##flagname); \
 } \
@@ -2675,7 +2680,6 @@ do {									\
 
 #endif
 
-extern void ext4_update_dynamic_rev(struct super_block *sb);
 extern int ext4_update_compat_feature(handle_t *handle, struct super_block *sb,
 					__u32 compat);
 extern int ext4_update_rocompat_feature(handle_t *handle,

fs/ext4/inode.c

@@ -5345,7 +5345,6 @@ static int ext4_do_update_inode(handle_t *handle,
 		err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh);
 		if (err)
 			goto out_brelse;
-		ext4_update_dynamic_rev(sb);
 		ext4_set_feature_large_file(sb);
 		ext4_handle_sync(handle);
 		err = ext4_handle_dirty_super(handle, sb);

fs/ext4/super.c

@@ -2249,7 +2249,6 @@ static int ext4_setup_super(struct super_block *sb, struct ext4_super_block *es,
 		es->s_max_mnt_count = cpu_to_le16(EXT4_DFL_MAX_MNT_COUNT);
 	le16_add_cpu(&es->s_mnt_count, 1);
 	ext4_update_tstamp(es, s_mtime);
-	ext4_update_dynamic_rev(sb);
 	if (sbi->s_journal)
 		ext4_set_feature_journal_needs_recovery(sb);