linux-ext4 - Re: on disk format: value of bg_inode_table

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Date:	Thu, 29 Jan 2009 11:47:29 +0000 (GMT)
From:	Etienne Lorrain <etienne_lorrain@...oo.fr>
To:	Theodore Tso <tytso@....edu>
Cc:	Andreas Dilger <adilger@....com>, linux-ext4@...r.kernel.org
Subject: Re: on disk format: value of bg_inode_table_hi?

Theodore Tso <tytso@....edu> wrote:
> bg_inode_table_hi doesn't exist on a small filesystem. 
> You need to take a look at if INCOMPAT_64BIT is not set,
> or if INCOMPAT_64BIT is set and s_desc_size is 32, then
> only the first 32 bytes of struct ext4_group_desc are
> in use --- which look exactly the same as ext2_group_desc.
> 
> So there is no problem here.  Just a misunderstanding of
> the filesystem format.
> 
> 						- Ted

 Thanks a lot; and sorry, I should have guessed myself that
the field is not there when s_desc_size is too small,
whatever the value of INCOMPAT_64BIT.

 May I ask confirmation of this 2 points on the list too:
- the array of inode in the inode_table is an array where
 each inode has the size superblock->s_inode_size (or
 EXT2_GOOD_OLD_INODE_SIZE) whatever s_min_extra_isize,
 s_want_extra_isize, inode->i_extra_isize because
 the "extra" size of an inode is not stored in the
 inode_table.

- If I only access the ext4 filesystem readonly, I do not
 have any difference considering the flags of the superblock:
 EXT4_FEATURE_INCOMPAT_META_BG, EXT4_FEATURE_INCOMPAT_MMP,
 EXT4_FEATURE_INCOMPAT_FLEX_BG. That is, I do not want to
 allocate any block, so I should not refuse to "mount" an
 ext4fs whatever the value of these flags.
 I do not know anything about EXT4_FEATURE_INCOMPAT_MMP...

 Thanks in advance,
 Etienne.


      
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