Re: [Qemu-devel] [PATCH] qemu-img create: add -o nocow option

[Kevin Wolf <kwolf@redhat.com>]

Am 21.11.2013 um 09:51 hat Stefan Hajnoczi geschrieben:
> On Thu, Nov 21, 2013 at 11:33:56AM +0800, Chunyan Liu wrote:
> > 2013/11/20 Stefan Hajnoczi <stefanha@gmail.com>
> > 
> > > On Wed, Nov 20, 2013 at 04:50:29PM +0800, Chunyan Liu wrote:
> > > >  block/cow.c               |   22 ++++++++++++++++++++++
> > > >  block/qcow.c              |   22 ++++++++++++++++++++++
> > > >  block/qcow2.c             |   22 ++++++++++++++++++++++
> > >
> > > I think you can avoid modifying all the image formats:
> > >
> > > .bdrv_create() functions pass options to bdrv_create_file().  Therefore
> > > an image format like qcow2 does not need to parse the nocow option
> > > itself.  Only raw-posix.c:.bdrv_create() needs to know about the nocow
> > > option.
> > >
> > >
> > In existing code, options passed to bdrv_create_file contains no option in
> > fact.
> > 
> > And if we pass all options to bdrv_create_file directly, raw-posix.c:
> > .bdrv_create() will get NOCOW option but at the same time get SIZE option,
> > it
> > will create a file with total size. For cow/qcow/qcow2, I suppose it's not
> > expected? In current code, bdrv_create_file will create a zero-sized image
> > for
> > cow/qcow/qcow2.
> 
> I see what the problem is: the loop that parses options does options++.
> So by the time it has processed them the options pointer will be NULL or
> point to a terminator option (option->name == NULL).
> 
> I was confused because there has been a patch series which changes
> .bdrv_create() option parsing.  But I forgot it hasn't been merged.
> https://lists.gnu.org/archive/html/qemu-devel/2013-08/msg01695.html
> 
> Kevin: Have you looked at .bdrv_create() QEMUOptionParameter removal
> recently?  Otherwise I'm inclined to merge Chunyan's patch - we can
> always refactor the code later when QEMUOptionParameter is removed.

No, I haven't. I think the QemuOpts conversion series was relatively
close, but it seems nobody is working on it any more. Someone should
probably pick it up and finish it.

Kevin