Re: [RFC PATCH v2 7/7] vfio-ccw: Add support for the CRW irq

[Cornelia Huck <cohuck@redhat.com>]

On Thu,  6 Feb 2020 22:45:09 +0100
Eric Farman <farman@linux.ibm.com> wrote:

> From: Farhan Ali <alifm@linux.ibm.com>
> 
> The CRW irq will be used by vfio-ccw to notify the userspace
> about any CRWs the userspace needs to handle. Let's add support
> for it.
> 
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> 
> Notes:
>     v1->v2:
>      - Add a loop to continually read region while data is
>        present, queueing CRWs as found [CH]
>     v0->v1: [EF]
>      - Check vcdev->crw_region before registering the irq,
>        in case host kernel does not have matching support
>      - Split the refactoring changes to an earlier (new) patch
>        (and don't remove the "num_irqs" check in the register
>        routine, but adjust it to the check the input variable)
>      - Don't revert the cool vfio_set_irq_signaling() stuff
>      - Unregister CRW IRQ before IO IRQ in unrealize
>      - s/crw1/crw0/
> 
>  hw/vfio/ccw.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 

> @@ -265,6 +266,40 @@ static void vfio_ccw_reset(DeviceState *dev)
>      ioctl(vcdev->vdev.fd, VFIO_DEVICE_RESET);
>  }
>  
> +static void vfio_ccw_crw_notifier_handler(void *opaque)
> +{
> +    VFIOCCWDevice *vcdev = opaque;
> +    struct ccw_crw_region *region = vcdev->crw_region;
> +    CRW crw;
> +    int size;
> +    uint8_t rsc, erc;
> +
> +    if (!event_notifier_test_and_clear(&vcdev->crw_notifier)) {
> +        return;
> +    }
> +
> +    do {
> +        memset(region, 0, sizeof(*region));
> +        size = pread(vcdev->vdev.fd, region, vcdev->crw_region_size,
> +                     vcdev->crw_region_offset);
> +
> +        if (size == -1) {
> +            error_report("vfio-ccw: Read crw region failed with errno=%d", errno);
> +            break;
> +        }
> +
> +        if (size == 0 || region->crw0 == 0) {

Does it make any sense to expect both of them as an indication that
there are no more crws at the moment? Grabbing a zeroed crw makes the
most sense as a stop condition, I think.

Also, I'm not sure anymore whether having space for two crws makes too
much sense. If we have a case in the future where we get two chained
crws, the code will retry anyway and just fetch the chained crw and
queue it, wouldn't it?

> +            /* No more CRWs to queue */
> +            break;
> +        }
> +
> +        memcpy(&crw, &region->crw0, sizeof(CRW));
> +        rsc = (crw.flags & 0x0f00) >> 8;
> +        erc = crw.flags & 0x003f;

I think we already have something for that... ah yes,
CRW_FLAGS_MASK_RSC and CRW_FLAGS_MASK_ERC.

> +        css_queue_crw(rsc, erc, 0, 0, crw.rsid);

...or maybe an alternative interface that allows us to queue a
ready-made crw?

> +    } while (1);
> +}
> +
>  static void vfio_ccw_io_notifier_handler(void *opaque)
>  {
>      VFIOCCWDevice *vcdev = opaque;