linux-ext4 - Re: Regular ext4 error warning with HD in USB dock

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Date:	Sat, 8 Jan 2011 09:05:20 +0100
From:	Rogier Wolff <R.E.Wolff@...Wizard.nl>
To:	Amir Goldstein <amir73il@...il.com>
Cc:	Ted Ts'o <tytso@....edu>, Ric Wheeler <rwheeler@...hat.com>,
	Rogier Wolff <R.E.Wolff@...wizard.nl>,
	Con Kolivas <kernel@...ivas.org>, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org
Subject: Re: Regular ext4 error warning with HD in USB dock

On Fri, Jan 07, 2011 at 11:07:23PM +0200, Amir Goldstein wrote:
> On Fri, Jan 7, 2011 at 9:41 PM, Amir Goldstein <amir73il@...il.com> wrote:
> > On Fri, Jan 7, 2011 at 7:26 AM, Ted Ts'o <tytso@....edu> wrote:
> >> Am I missing something?  The kernel stores up to 3k worth of data, on
> >> a 4k block file system.  Whereas e2fsck patch blindly assume 2k worhth
> >> of data regardless of the block size.  The kernel patch looks ok, but
> >> the e2fsprogs patch seems badly broken....
> 
> So it's not badly broken, it copies blocksize-2K, which is clumsily
> written like this:
> +	int len = ctx->fs->blocksize - 2*SUPERBLOCK_OFFSET;

So this should be: 

  int len = ctx->fs->blocksize - SUPERBLOCK_OFFSET - sizeof (<superblock>);

Although those two numbers are equal right now, there is no reason to
assume that they will remain so in the future. So if the superblock
size (or the offset) changes in the future, it's much better to have
programmed this so that it will keep on working as opposed to getting
to deal with ugly bugs in code that hasn't changed in years...

	Roger. 
-- 
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