linux-ext4 - Re: [PATCH 10/22] ext4: Verify and calculate checksums for extent tree blocks

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Message-ID: <20111205164015.GD32031@thunk.org>
Date:	Mon, 5 Dec 2011 11:40:15 -0500
From:	Ted Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	Martin K Petersen <martin.petersen@...cle.com>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Amir Goldstein <amir73il@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Mingming Cao <cmm@...ibm.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Coly Li <colyli@...il.com>
Subject: Re: [PATCH 10/22] ext4: Verify and calculate checksums for extent
 tree blocks

On Mon, Nov 28, 2011 at 03:27:25PM -0800, Darrick J. Wong wrote:
>  /*
> + * This is the extent tail on-disk structure.
> + * All other extent structures are 12 bytes long.  It turns out that
> + * block_size % 12 >= 4 for all valid block sizes (1k, 2k, 4k).

More generally, block_size % 12 is >= 4 for all powers of 2 greater
than 12 bytes.  I'd probably remove (1k, 2k, 4k) because that might
scare people who might say, "hey!  I'm using a 16k block size on my
HPC system running on a Power or Itanium box --- am I going to be OK?".
Valid block sizes go up to the page size of the hardware in question...

      	    	     	       	    	    - Ted
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