Re: bin/45072 (fsck_ext2fs dosn't work well with ext2fs's without alternate superblocks)

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR bin/45072; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: dholland%NetBSD.org@localhost, tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: bin/45072 (fsck_ext2fs dosn't work well with ext2fs's without 
alternate
         superblocks)
Date: Sat, 18 Jun 2011 02:33:22 +0900

 > Can you clear up with the linux ext2fs folks what the correct behavior of
 > linux e2fsck should be?
 
 I'm afraid there is no proper documents other than sources of e2fsprogs.. 
 
 > One possibility suggested was that the volume might have gotten resized,
 > which would move the alternate superblocks.
 
 IIUC ext2fs uses a fixed block number per block group (cylinder group)
 so alternate superblocks are always allocated at the same blocks even
 after resize if block size is not changed.
 (see also cg_has_sb() in <ufs/ext2fs/ext2fs.h>)
 
 > Another possibility is that
 > Ubuntu did something ext4-related that our ext2 tools don't understand.
 
 At least fsck_ext2fs(8) seems to check INCOMPATIBLE FEATURE bits
 in superblock. (though I'm not sure how Linux guys take care
 of backward compatibititty)
 ---
 Izumi Tsutsui