On Wed, Feb 19, 2025 at 04:23:26PM +0530, prashant patil wrote:
> Hello All,
> Hope this email finds you well.
>
> I have been trying with qemu for a while now, and have come across a
> problem specific to dirty bitmaps. I have enabled bitmap on the qcow2 disk
> image using 'qemu-img bitmap' command, exposed the bitmap over a unix
> socket using 'qemu-nbd' command. Now when I try to read the bitmap using
> 'qemu-img map' command with 'x-dirty-bitmap=qemu:dirty-bitmap:{bitmap}'
> option, I get one single extent which shows that the entire disk is dirty.
> Note that the disk size is 5 GB, and has only a few MB of data in it, and
> had added very small data after the bitmap was enabled. Bitmap output has
> been pasted below.
Can you show the exact sequence of command lines you used to create
the image, dirty a portion of it, then start up the qemu-nbd process
to inspect it? As written, I can't reproduce your issue, but I know
it sounds similar to tests/qemu-iotests/tests/qemu-img-bitmaps which
does what you're talking about, so I know the code works and have to
suspect you may have missed a step or reordered things in such a way
that the entire bitmap is reading as dirty.
>
> [{ "start": 0, "length": 5368709120, "depth": 0, "present": true, "zero":
> false, "data": true, "compressed": false, "offset": 0}]
>
> Can someone please help me understand why the bitmap content shows the
> entire disk as dirty?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
