Re: [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size

[Jason Dillaman]

On Thu, Apr 11, 2019 at 9:02 AM Stefano Garzarella <address@hidden> wrote:
>
> On Thu, Apr 11, 2019 at 08:35:44AM -0400, Jason Dillaman wrote:
> > On Thu, Apr 11, 2019 at 7:00 AM Stefano Garzarella <address@hidden> wrote:
> > >
> > > RBD APIs don't allow us to write more than the size set with rbd_create()
> > > or rbd_resize().
> > > In order to support growing images (eg. qcow2), we resize the image
> > > before RW operations that exceed the current size.
> >
> > What's the use-case for storing qcow2 images within a RBD image? RBD
> > images are already thinly provisioned, they support snapshots, they
> > can form a parent/child linked image hierarchy.
> >
>
> Hi Jason,
> I understand your point of view, maybe one use case could be if you have
> a qcow2 image and you want to put it in the rdb pool without convert it.
>
> I'm going through this BZ [1] and I'll ask if they have other
> use cases in mind.

Assuming no good use-cases, perhaps it would just be better to make
the qemu-img error messages more clear.

> Anyway, if we want to support only raw format on RBD driver, maybe we
> should return something different from current behaviour, also avoiding
> to create the image:
>
> $ qemu-img create -f qcow2 rbd:test/qcow.img 1G
>   qemu-img: rbd:test/qcow.img: Could not write qcow2 header: Invalid argument
>
> What do you think?
>
> Thanks,
> Stefano
>
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1171007



-- 
Jason