Re: [PATCH] vdpa_sim_blk: add support for VIRTIO_BLK_T_FLUSH

[Stefano Garzarella]

On Fri, Apr 29, 2022 at 10:46:40AM +0800, Jason Wang wrote:
> On Thu, Apr 28, 2022 at 11:13 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
> > The simulator behaves like a ramdisk, so we don't have to do
> > anything when a VIRTIO_BLK_T_FLUSH request is received, but it
> > could be useful to test driver behavior.
> >
> > Let's expose the VIRTIO_BLK_F_FLUSH feature to inform the driver
> > that we support the flush command.
> >
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim_blk.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > index 42d401d43911..a6dd1233797c 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > @@ -25,6 +25,7 @@
> >  #define DRV_LICENSE  "GPL v2"
> >
> >  #define VDPASIM_BLK_FEATURES   (VDPASIM_FEATURES | \
> > +                                (1ULL << VIRTIO_BLK_F_FLUSH)    | \
> >                                  (1ULL << VIRTIO_BLK_F_SIZE_MAX) | \
> >                                  (1ULL << VIRTIO_BLK_F_SEG_MAX)  | \
> >                                  (1ULL << VIRTIO_BLK_F_BLK_SIZE) | \
> > @@ -166,6 +167,17 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
> >                 pushed += bytes;
> >                 break;
> >
> > +       case VIRTIO_BLK_T_FLUSH:
> > +               if (sector != 0) {
> > +                       dev_err(&vdpasim->vdpa.dev,
> > +                               "A driver MUST set sector to 0 for a VIRTIO_BLK_T_FLUSH request - sector: 0x%llx\n",
> > +                               sector);
>
> If this is something that could be triggered by userspace/guest, then
> we should avoid this.

It can only be triggered by an erratic driver.

I was using the simulator to test a virtio-blk driver that I'm writing 
in userspace and I forgot to set `sector` to zero, so I thought it would 
be useful.

Do you mean to remove the error message?

Thanks,
Stefano