linux-ext4 - Re: [PATCH 2/2] e2image: add -a switch to include all data

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Date:	Fri, 17 Feb 2012 16:39:40 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
cc:	"Ted Ts'o" <tytso@....edu>, Phillip Susi <psusi@...ntu.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] e2image: add -a switch to include all data

On Fri, 17 Feb 2012, Lukas Czerner wrote:

> On Fri, 17 Feb 2012, Ted Ts'o wrote:
> 
> > On Fri, Feb 17, 2012 at 10:17:43AM +0100, Lukas Czerner wrote:
> > > 
> > > So the problem actually is that I have made some assumptions, like for
> > > example that all data are laid out sequentially (because it is how we
> > > are creating the qcow2 images with e2image) and possibly more. 
> > 
> > So if your code doesn't work correctly if the block numbers are
> > monotonically increasing in the qcow2 image, I would *have* to assume
> > there would be plenty of qemu-generated images files that don't have
> > this constraint (i.e., suppose you write blocks 10000, 42, 16, and 24
> > while running under qemu, presumably that is the order the blocks
> > would be written and would show up in the qcow2 file).
> > 
> > Or am I misunderstanding what you are saying here; is it that you are
> > fairly sure the code will break if the data is not laid out
> > sequentially, or that you've never tested this case?
> 
> Hi Ted,
> 
> as I said I have never tested this. Well, actually I did some very
> limited testing, but since this was not (and still is not right?) the
> scope of e2image I did not care enough to test that extensively enough
> to be sure that it generally works with qcow2 images other than those
> generated with e2image. But I think it should work.
> 
> Also I suppose that qemu is being a bit smarter than just writing every
> extent out so it does not seek madly back and forth when the image is
> not laid out sequentially. e2image does not do that.

ehm..I meant, e2image does not do any smart things there, just seek and
write.

> 
> Thanks!
> -Lukas
> 
> > 
> > Regards,
> > 
> > 						- Ted
> > --
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