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Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number durin
From: |
Arthur Gautier |
Subject: |
Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert |
Date: |
Thu, 30 Oct 2014 15:28:20 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Oct 30, 2014 at 06:27:20PM +0800, Fam Zheng wrote:
> On Thu, 10/30 10:09, Arthur Gautier wrote:
> > On Wed, Oct 29, 2014 at 09:28:52AM +0800, Fam Zheng wrote:
> > > On Tue, 10/28 16:00, Stefan Hajnoczi wrote:
> > > > On Thu, Oct 23, 2014 at 10:03:25AM +0200, Markus Armbruster wrote:
> > > > > Michael Tokarev <address@hidden> writes:
> > > > >
> > > > > > On 10/22/2014 05:25 PM, Arthur Gautier wrote:
> > > > > >> We can not rely on int cast to get a correct number of cylinders.
> > > > > >> The
> > > > > >> cylinders information was wrong in 49.9999% of cases.
> > > > > >>
> > > > > >> This ensures the cylinders always gets the ceiling value.
> > > > > >
> > > > > > Good thing, especially the good probability :), and also a good
> > > > > > patch
> > > > > > which comes with a test.
> > > > > >
> > > > > > But I wonder if anything can break this way? Migration, windows
> > > > > > guest
> > > > > > being unable to find its partitions, something else?
> > >
> > > I'd like to hear an answer to this question too, so we know why it's
> > > right and
> > > worth to have.
> > >
> > Sincerely, I didn't tried myself.
> >
> > > > > >
> > > > > > And more. What-if our drive size in cylinders will be larger than
> > > > > > the size in bytes? The proposed div_round_up() will increase number
> > > > > > of cylinders, so size in CHS will be larger than size in bytes.
> > > > > > Maybe
> > > > > > there was a reason why originally the size in cylinders was
> > > > > > calculated
> > > > > > by truncating extra fractional part? What-if guest will try to
> > > > > > access
> > > > > > the very last CHS which is incomplete?
> > >
> > > I don't remember a reason why truncating (I doubt there is any), OTOH I'm
> > > not
> > > sure what is the right thing to do if the guest tries to write to the last
> > > incomplete CHS either.
> > >
> > > Fam
> >
> > Maybe we can expand the disk to the size matching cylinders * sectors *
> > sector_size and issue a warning to the user? This way it will always be
> > safe.
> >
>
> Possible, but I don't know if it's worth it. Could you explain what doesn't
> work now, in order to show *why* you need this change?
>
> Thanks,
> Fam
Please take a look at the test in the patch. I have been able to
generate an image with a number of cylinders of zero which I believe is
wrong.
--
\o/ Arthur
G Gandi.net
- [Qemu-trivial] [PATCH] vmdk: Fix cylinders number during convert, Arthur Gautier, 2014/10/22
- Re: [Qemu-trivial] [PATCH] vmdk: Fix cylinders number during convert, Michael Tokarev, 2014/10/23
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Markus Armbruster, 2014/10/23
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Stefan Hajnoczi, 2014/10/28
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Fam Zheng, 2014/10/28
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Arthur Gautier, 2014/10/30
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Fam Zheng, 2014/10/30
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert,
Arthur Gautier <=
- Re: [Qemu-trivial] [Qemu-devel] [PATCH] vmdk: Fix cylinders number during convert, Fam Zheng, 2014/10/31