From: "Jose R. Santos" <jrs@us.ibm.com>
Subject: Re: [PATCH 15/15][e2fsprogs] 64-bit mke2fs cleanup
Date: Wed, 16 Jul 2008 10:18:17 -0500
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Cc: Goswin von Brederlow <goswin-v-b@web.de>,
	linux-ext4@vger.kernel.org
To: Theodore Tso <tytso@mit.edu>
In-Reply-To: <20080716145429.GA2167@mit.edu>
Sender: linux-ext4-owner@vger.kernel.org

On Wed, 16 Jul 2008 10:54:29 -0400
Theodore Tso <tytso@mit.edu> wrote:

> On Wed, Jul 16, 2008 at 09:09:31AM -0500, Jose R. Santos wrote:
> > No, ext2fs_get_device_size2() should return EFBIG size if the device is
> > larger than 48-bit.  I need to fix that on ext2fs_get_device_size2() but 
> > this check here is ok.
> 
> No, please don't do that.  Make it reuturn EFBIG if the device won't
> fit in a blk64_t type (i.e., larger than 64-bits).  In mke2fs, there
> should be a separate check to make sure the size is no larger than
> 48-bits.  Otherwise, at some future point, perhaps we might enhance
> ext4 to support full a 64-bit physical block number, and then we would
> have to make behavioural changes to ext2fs_get_device_size2() that
> would necessitate renaming the function yet again.
> 
> It's really important when doing library design to think about future
> expandability.

This would not be a API or ABI change so I don't see why another
renaming function would be needed.  It also doesn't change the
behavior of ext2fs_get_device_size2() since it returns EFBIG when a
device is larger than what e2fsprogs currently supports, whether that
48bit or 64bits.  Putting the limit ext2fs_get_device_size2() avoid
folks from abusing something that probably isn't supported. 

> 						- Ted

-JRS