linux-ext4 - Re: [patch 07/12] rfc: 2fsprogs update

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Message-ID: <20060926173700.GD4219@thunk.org>
Date:	Tue, 26 Sep 2006 13:37:00 -0400
From:	Theodore Tso <tytso@....edu>
To:	Alexandre Ratchov <alexandre.ratchov@...l.net>
Cc:	linux-ext4@...r.kernel.org,
	Jean-Pierre Dion <jean-pierre.dion@...l.net>
Subject: Re: [patch 07/12] rfc: 2fsprogs update

On Tue, Sep 26, 2006 at 04:48:32PM +0200, Alexandre Ratchov wrote:
> convert all 32bit on-disk block number definitions (currently __u32,
> blk_t, unsigned long, unsigned int...) to pblk_t that is defined as
> __u32. In this way we are sure that blk_t is used only in memory.
> Later, this would allow to make blk_t 64bit without disturbing any
> programs (this would just eat more momory and use 64bit arithmetic).

I *really* dislike this approach, because it makes it very hard to
prove that we got all of the conversions right --- any mistakes about
which instances of blk_t need to become pblk_t, and which are supposed
to stay blk_t, and we end up breaking our ABI compatibility.  And
let's just say I have higher standards than Greg KH has shown with
udev.  :-)    

I also don't like pblk_t, because it's not at all obvious what it
means.  And what if we want to support 64-bit logicial blocks someday?
Then it's another painful exercise to figure out which blk_t get
separated to lblk_t, etc.   

So my plan is to introduce a new type, blk64_t, and create new
interfaces, such as ext2fs_extent_iterate(), which will use the new
type --- and which will work with old-style indirect block inodes as
well (it will translate indirect blocks into extents).  

					- Ted
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