From 92bd5b69d7e7096fffc8cab08cc6886fe22df77d Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sat, 9 Aug 2014 12:33:11 -0400
Subject: [PATCH 2/5] 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>
---
 resize/resize2fs.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index a73390de..a2ff29ad 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -461,6 +461,13 @@ 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;
+	}
+
 	/*
 	 * If we are shrinking the number of block groups, we're done
 	 * and can exit now.
@@ -946,13 +953,15 @@ 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;
-	}
 
 	if (old_blocks == new_blocks) {
 		retval = 0;
-- 
2.21.3