Re: [Qemu-devel] [PATCH v6 00/20] VHDX log replay and write support, .bdrv_create()

[Jeff Cody]

On Tue, Oct 01, 2013 at 03:41:04PM +0200, Stefan Hajnoczi wrote:
> On Wed, Sep 25, 2013 at 05:02:45PM -0400, Jeff Cody wrote:
> > 
> > This patch series contains the initial VHDX log parsing, replay,
> > write support, and image creation.
> > 
> > === v6 changes ===
> > https://github.com/codyprime/qemu-kvm-jtc/tree/vhdx-write-v6-upstream
> > 
> > Rebased to latest qemu/master:
> > 
> > Patch 16/20: .bdrv_create() propagates Error, and bdrv_unref() used
> >              instead of bdrv_delete().
> > 
> > Patch 17 & 18 are already included in another series:
> >     [PATCH v3 0/3] qemu-iotests with sample images, vhdx test, cleanup
> > 
> > They are included here to provide a base for patches 19 & 20.  If the above
> > series is applied before this series, then patches 17 and 18 can be ignored.
> > 
> > Patch 19/20: In qemu-io tests _make_test_img(), filter out vhdx-specific
> >              options for .bdrv_create().
> > 
> > Patch 20/20: Add VHDX write test case to 064.
> 
> Sorry for the late review.  Feel free to poke Kevin or me if we're being
> slow - the squeaky wheel gets the grease.
> 
> I left comments on a couple of the core journal and write patches.  It
> looks pretty good overall.
> 
> How is the journal code tested?  IIUC the sample image file does not
> have a dirty journal.  Please try to include an image that Hyper-V
> created with a dirty journal so we can be sure flushing the journal
> works.

Getting Hyper-V generated files with journals is a bit challenging.
The methodology I've been using is a Linux guest under Hyper-V,
generating a lot of guest i/o that will cause metadata updates (e.g. dd
if=/dev/sda of=/dev/sdb, etc..). While this is going on, I hit the
reset button on the server.  Kinda messy, but it works, if not very
deterministically.  I initially tried just killing the process, but I
was unable to do that and obtain a dirty log.

The problems with the images I've created in this manner is they are
much too large to put in our repo.  However, if I write repetitive
data, that should allow the image to be compressed adequately... I'll
give that a try.

I've tested the other direction too (which is much easier) - create a
VHDX image under QEMU, leave a dirty journal, and then open the image
file with the dirty journal under Hyper-V.  It replayed it, and the
sha1sum of the affected file inside the image was correct after replay.