linux-ext4 - Re: [PATCH 14/31] libext2fs: Fix ext2fs_open2() truncation of the superblock parameter

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Message-ID: <20131008174729.GJ6860@birch.djwong.org>
Date:	Tue, 8 Oct 2013 10:47:29 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 14/31] libext2fs: Fix ext2fs_open2() truncation of the
 superblock parameter

On Tue, Oct 08, 2013 at 11:58:59AM -0400, Theodore Ts'o wrote:
> On Mon, Sep 30, 2013 at 06:28:12PM -0700, Darrick J. Wong wrote:
> > Since it's possible for very large filesystems to store backup superblocks at
> > very large (> 2^32) block numbers, we need to be able to handle the case of a
> > caller directing us to read one of these high-numbered backups.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> 
> Hmm... This is technically true, but I'm wondering how much we should
> care.  In practice, users almost always use the first couple of backup
> superblocks.  I could imagine a situation with a RAID array where the
> first disk(s) were trashed, so we needed to use a backup superblock
> beyond 2**32, but it's a bit unlikely.

True, it seems unlikely now that one would ever need to use the backup sbs
beyond 2^32, but since mke2fs is writing them there, we ought to be able to use
them.

For now, though, it's truncating the top 32 bits of a (usually) user-specified
value, so if we don't extend the API we ought to at least complain and exit.

> If there was some other reason why we needed to add a new ext2fs_open3
> variant, it would certainly be a good thing to fix.  But I'm wondering
> if it's worth adding a new interface just for this.
> 
> Is there perhaps any other extensions to ext2fs_open() that we might
> want to make, either now or in the future?

I don't have any off the top of my head, but I'll think about it.

--D
> 
> Regards,
> 
> 						- Ted
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