Does diffoscope compares disk partitions

Mattia Rizzolo mattia at
Wed Mar 1 18:16:48 UTC 2023

On Wed, Mar 01, 2023 at 10:55:41AM +0000, Chris Lamb wrote:
> > Does it support disk partitions or do I missing something?
> The short answer is that that diffoscope *should* support comparing your
> partition images properly, instead of falling back to a raw
> xxd(1) comparison. The reason diffoscope doesn't do that right now is
> either due to a bug, or we just need to extend support for this
> particular type of partition.

Mhh, I don't think it should.
I don't reckon ever seeing anything related to GPT or MBR, so I don't
think diffoscope supports whole disk images with a partition tables.

> Correctly detecting DOS/MBR files is somewhat more fiddly than one
> might think, but the pertinent part of the debug log is this:


For a time we used the "DOS/MBR" as flag for fat16/32 images, however we
moved over to use the headers instead.

I don't think we have anything actually handling an actual MBR, however.
And this is a gpt partition table, which is yet different, and I think
also not handled.

> > image1.wic not identified by any comparator. Magic says: DOS/MBR boot 
> >  sector; partition 1 : ID=0xee, start-CHS (0x0,0,2), end-CHS 
> >  (0x3ff,255,63), startsector 1, 12546899 sectors, extended partition 
> >  table (last)
> Would it be possible for you to share the two .wic images somewhere?
> In fact, if you could re-file this issue in our bug tracker, that
> would be great:
> (And just for clarity, the ".wic" files are files containing raw
> partitions, but the ".disk" files contain entire disk images including
> a partition table?)

.disk is a new one for me, but looking at the diffoscope output from
Venkata I reckon this is actually a single file system (ext4) image?

Also, I never saw a .wic file (never heard of, even), but since Venkata
shared a `fdisk -l` of such file, I reckon that one is a full disk disk
dump including a partition table.

So, overall, I actually don't think that diffoscope has the requested
support, and it's not "just" a bug of failed identification.

                        Mattia Rizzolo

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