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

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Message-ID: <20120216231745.GC26473@thunk.org>
Date:	Thu, 16 Feb 2012 18:17:45 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Phillip Susi <psusi@...ntu.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] e2image: add -a switch to include all data

> +You can convert a qcow2 image into a raw image with:
> +.PP
> +.br
> +\	\fBe2image \-r hda1.qcow2 hda1.raw\fR
> +.br
> +.PP
> +This can be useful to write a qcow2 image containing all data to a
> +sparse image file where it can be loop mounted, or to a disk partition

As I recall Lukas disclaimed a guarantee that the code would work on
qcow2 images that weren't generated by e2image.  (In particular, it
definitely doesn't support compressed or encrypted qcow2 images.)

So we need to make sure we add the appropriate disclaimers that this
might not work on qcow2 images generated by tools other than e2image.

If someone would like to work on improving lib/ext2fs/qcow2.c to add
those missing features, and more importantly, add test cases, it would
be great if our qcow2 support could be made more complete.

> +.PP
> +.SH INCLUDING DATA
> +Normally
> +.B e2image
> +only includes fs metadata, not regular file data.  The 
> +.B \-a
> +option can be specified to include all data.  This will
> +give an image that is suitible to use to clone the entire FS or
> +for backup purposes.  Note that this option only works with the
> +raw or QCOW2 formats.

It will only work for raw images.  The QCOW2 format uses an entirely
different code path, since we don't have an QCOW2 io_manager
abstraction.  That was my original hope, but that's not how our qcow2
support was implemented, so it won't work, and we should probably give
a reasonable warning if someone tries to use the -a flag with anything
other than a raw file system image for e2image's input.

						- Ted

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