resize2fs: disable the meta_bg feature if necessary

When shrinking a file system, if the number block groups drops below
the point where we started using the meta_bg layout, disable the
meta_bg feature and set s_first_meta_bg to zero.  This is necessary to
avoid creating an invalid/corrupted file system after the shrink.

Addresses-Debian-Bug: #756922

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Marcin Wolcendorf <antymat+debian@chelmska.waw.pl>
Tested-by: Marcin Wolcendorf <antymat+debian@chelmska.waw.pl>

diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 9641b1e..b3755f6 100644 (file)
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -489,6 +489,13 @@ retry:
                fs->super->s_reserved_gdt_blocks = new;
        }
 
+       if ((fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG) &&
+           (fs->super->s_first_meta_bg > fs->desc_blocks)) {
+               fs->super->s_feature_incompat &=
+                       ~EXT2_FEATURE_INCOMPAT_META_BG;
+               fs->super->s_first_meta_bg = 0;
+       }
+
        /*
         * Update the location of the backup superblocks if the
         * sparse_super2 feature is enabled.
@@ -998,13 +1005,15 @@ static errcode_t blocks_to_move(ext2_resize_t rfs)
                ext2fs_mark_block_bitmap2(rfs->reserve_blocks, blk);
        }
 
-       if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG) {
+       if (old_fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG)
                old_blocks = old_fs->super->s_first_meta_bg;
+       else
+               old_blocks = old_fs->desc_blocks +
+                       old_fs->super->s_reserved_gdt_blocks;
+       if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG)
                new_blocks = fs->super->s_first_meta_bg;
-       } else {
-               old_blocks = old_fs->desc_blocks + old_fs->super->s_reserved_gdt_blocks;
+       else
                new_blocks = fs->desc_blocks + fs->super->s_reserved_gdt_blocks;
-       }
 
        retval = reserve_sparse_super2_last_group(rfs, meta_bmap);
        if (retval)