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

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Message-ID: <20110109081249.GA32496@bitwizard.nl>
Date:	Sun, 9 Jan 2011 09:12:49 +0100
From:	Rogier Wolff <R.E.Wolff@...Wizard.nl>
To:	Ted Ts'o <tytso@....edu>
Cc:	Rogier Wolff <R.E.Wolff@...Wizard.nl>,
	Amir Goldstein <amir73il@...il.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	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 Sat, Jan 08, 2011 at 05:00:59PM -0500, Ted Ts'o wrote:
> On Sat, Jan 08, 2011 at 09:05:20AM +0100, Rogier Wolff wrote:
> > 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...
> 
> No.  The superblock nor its offset will never change.  It's like the
> syscall ABI, only worse.  If we changed it would break *everybody*.
> Fortunately there is a huge amount of space left over in the 1024 byte
> superblock.

It's called defensive programming. It prevents bugs before they
happen. By your reasoning you could've written 2048 or 0x800 there.

My version:

  - documents why something is subtracted from the blockszize and how
    much.
  - keeps on working even if the superblock would oddly change size
    in the future. Even if now you don't expect that to happen ever.


	Roger. 


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