linux-kernel - Re: [PATCH] vdpa_sim_blk: add `capacity` module parameter

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Message-ID: <CACGkMEurseUpMKaiLpJEkcT9U_tmqm4yqp3OgR--6XnAY=C9WQ@mail.gmail.com>
Date: Mon, 8 Jul 2024 15:59:34 +0800
From: Jason Wang <jasowang@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: Stefano Garzarella <sgarzare@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, virtualization@...ts.linux.dev, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, linux-kernel@...r.kernel.org, 
	Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH] vdpa_sim_blk: add `capacity` module parameter

On Mon, Jul 8, 2024 at 3:06 PM Cindy Lu <lulu@...hat.com> wrote:
>
> On Fri, 5 Jul 2024 at 20:42, Stefano Garzarella <sgarzare@...hat.com> wrote:
> >
> > On Fri, Jul 05, 2024 at 07:30:51AM GMT, Michael S. Tsirkin wrote:
> > >On Fri, Jul 05, 2024 at 01:28:21PM +0200, Stefano Garzarella wrote:
> > >> The vDPA block simulator always allocated a 128 MiB ram-disk, but some
> > >> filesystems (e.g. XFS) may require larger minimum sizes (see
> > >> https://issues.redhat.com/browse/RHEL-45951).
> > >>
> > >> So to allow us to test these filesystems, let's add a module parameter
> > >> to control the size of the simulated virtio-blk devices.
> > >> The value is mapped directly to the `capacity` field of the virtio-blk
> > >> configuration space, so it must be expressed in sector numbers of 512
> > >> bytes.
> > >>
> > >> The default value (0x40000) is the same as the previous value, so the
> > >> behavior without setting `capacity` remains unchanged.
> > >>
> > >> Before this patch or with this patch without setting `capacity`:
> > >>   $ modprobe vdpa-sim-blk
> > >>   $ vdpa dev add mgmtdev vdpasim_blk name blk0
> > >>   virtio_blk virtio6: 1/0/0 default/read/poll queues
> > >>   virtio_blk virtio6: [vdb] 262144 512-byte logical blocks (134 MB/128 MiB)
> > >>
> > >> After this patch:
> > >>   $ modprobe vdpa-sim-blk capacity=614400
> > >>   $ vdpa dev add mgmtdev vdpasim_blk name blk0
> > >>   virtio_blk virtio6: 1/0/0 default/read/poll queues
> > >>   virtio_blk virtio6: [vdb] 614400 512-byte logical blocks (315 MB/300 MiB)
> > >>
> > >> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> > >
> > >What a hack. Cindy was working on adding control over config
> > >space, why can't that be used?
> >
> > If it can be used easily with virtio-blk device too, it will be great.
> > @Cindy do you plan to support that changes for a virtio-blk device too?
> >
> Hi Stefano
> I plan to add support to change the vdpa device's configuration after
> it is created.

I think for Stefano's case, we can just implement it via provisioning
parameters?

Thanks

> In the first step, I want to use the vdpa tool to add
> support for changing the MAC address for the network device. the next
> step will also add MTU settings etc
> here is the link
> https://lore.kernel.org/all/20240708064820.88955-1-lulu@redhat.com/T/#t
>
> in the device part, the device needs to implement its function of
> int (*dev_set_attr)(struct vdpa_mgmt_dev *mdev, struct vdpa_device *dev,
>        const struct vdpa_dev_set_config *config);
> the configuration will be passed by struct vdpa_dev_set_config. I'm
> not sure if this kind of design is suitable for you? Really thanks and
> any comments are welcome
> thanks
> Cindy
>
>
> > In the mean time, for the simulator I thought that this change was fine.
> > It's just used for testing and debugging...
> >
> > My main question is how to use that when we have `shared_backend` set to
> > true, since we use that setting to test for example live migration. In
> > that case, how do we handle the size of the shared ramdisk between
> > devices?
> >
> > Thanks,
> > Stefano
> >
>