Ignore "safe" flag differences when e2fsck compares superblocks

Recent e2fsprogs (1.40.3 and higher) fsck compares primary superblock to
backups, and if things differ, it forces a full check.  However, the
kernel has a penchant for updating flags the first time a feature is
used - attributes, large files, etc.

This is a bad idea, and we should break the kernel of this habit,
especially for the ext4 feature flags.  But for now, let's make e2fsck
avoid forcing a full check and backup except when absolutely
necessary.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/e2fsck/super.c b/e2fsck/super.c
index a4835f7..954783e 100644 (file)
--- a/e2fsck/super.c
+++ b/e2fsck/super.c
@@ -773,8 +773,26 @@ void check_super_block(e2fsck_t ctx)
 
 /*
  * Check to see if we should backup the master sb to the backup super
- * blocks.
+ * blocks.  Returns non-zero if the sb should be backed up.
  */
+
+/*
+ * A few flags are set on the fly by the kernel, but only in the
+ * primary superblock.  This is actually a bad thing, and we should
+ * try to discourage it in the future.  In particular, for the newer
+ * ext4 files, especially EXT4_FEATURE_RO_COMPAT_DIR_NLINK and
+ * EXT3_FEATURE_INCOMPAT_EXTENTS.  So some of these may go away in the
+ * future.
+ *
+ * The kernel will set EXT2_FEATURE_COMPAT_EXT_ATTR, but
+ * unfortunately, we shouldn't ignore it since if it's not set in the
+ * backup, the extended attributes in the filesystem will be stripped
+ * away.
+ */
+#define FEATURE_RO_COMPAT_IGNORE       (EXT2_FEATURE_RO_COMPAT_LARGE_FILE| \
+                                        EXT4_FEATURE_RO_COMPAT_DIR_NLINK)
+#define FEATURE_INCOMPAT_IGNORE                (EXT3_FEATURE_INCOMPAT_EXTENTS)
+
 int check_backup_super_block(e2fsck_t ctx)
 {
        ext2_filsys     fs = ctx->fs;
@@ -814,10 +832,18 @@ int check_backup_super_block(e2fsck_t ctx)
                        continue;
                }
 
-#define SUPER_DIFFERENT(x) (fs->super->x != tfs->super->x)
+#define SUPER_INCOMPAT_DIFFERENT(x)    \
+       (( fs->super->x & ~FEATURE_INCOMPAT_IGNORE) !=  \
+        (tfs->super->x & ~FEATURE_INCOMPAT_IGNORE))
+#define SUPER_RO_COMPAT_DIFFERENT(x)   \
+       (( fs->super->x & ~FEATURE_RO_COMPAT_IGNORE) != \
+        (tfs->super->x & ~FEATURE_RO_COMPAT_IGNORE))
+#define SUPER_DIFFERENT(x)             \
+       (fs->super->x != tfs->super->x)
+
                if (SUPER_DIFFERENT(s_feature_compat) ||
-                   SUPER_DIFFERENT(s_feature_incompat) ||
-                   SUPER_DIFFERENT(s_feature_ro_compat) ||
+                   SUPER_INCOMPAT_DIFFERENT(s_feature_incompat) ||
+                   SUPER_RO_COMPAT_DIFFERENT(s_feature_ro_compat) ||
                    SUPER_DIFFERENT(s_blocks_count) ||
                    SUPER_DIFFERENT(s_inodes_count) ||
                    memcmp(fs->super->s_uuid, tfs->super->s_uuid,