On 5/23/2022 12:20 PM, Eugenio Perez Martin wrote:
On Sat, May 21, 2022 at 12:13 PM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
On 5/20/2022 10:23 AM, Eugenio Pérez wrote:
This operation is optional: It it's not implemented, backend feature bit
will not be exposed.
Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
---
include/linux/vdpa.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
index 15af802d41c4..ddfebc4e1e01 100644
--- a/include/linux/vdpa.h
+++ b/include/linux/vdpa.h
@@ -215,6 +215,11 @@ struct vdpa_map_file {
* @reset: Reset device
* @vdev: vdpa device
* Returns integer: success (0) or error (< 0)
+ * @stop: Stop or resume the device (optional, but it must
+ * be implemented if require device stop)
+ * @vdev: vdpa device
+ * @stop: stop (true), not stop (false)
+ * Returns integer: success (0) or error (< 0)
Is this uAPI meant to address all use cases described in the full blown
_F_STOP virtio spec proposal, such as:
--------------%<--------------
...... the device MUST finish any in flight
operations after the driver writes STOP. Depending on the device, it
can do it
in many ways as long as the driver can recover its normal operation if it
resumes the device without the need of resetting it:
- Drain and wait for the completion of all pending requests until a
convenient avail descriptor. Ignore any other posterior descriptor.
- Return a device-specific failure for these descriptors, so the driver
can choose to retry or to cancel them.
- Mark them as done even if they are not, if the kind of device can
assume to lose them.
--------------%<--------------
Right, this is totally underspecified in this series.
I'll expand on it in the next version, but that text proposed to
virtio-comment was complicated and misleading. I find better to get
the previous version description. Would the next description work?
```
After the return of ioctl, the device MUST finish any pending operations like
in flight requests. It must also preserve all the necessary state (the
virtqueue vring base plus the possible device specific states)
Hmmm, "possible device specific states" is a bit vague. Does it require
the device to save any device internal state that is not defined in the
virtio spec - such as any failed in-flight requests to resubmit upon
resume? Or you would lean on SVQ to intercept it in depth and save it
with some other means? I think network device also has internal state
such as flow steering state that needs bookkeeping as well.
A follow-up question is what is the use of the `stop` argument of false,
does it require the device to support resume? I seem to recall this is
something to abandon in favor of device reset plus setting queue
base/addr after. Or it's just a optional feature that may be device
specific (if one can do so in simple way).
-Siwei
that is required
for restoring in the future.
In the future, we will provide features similar to VHOST_USER_GET_INFLIGHT_FD
so the device can save pending operations.
```
Thanks for pointing it out!
E.g. do I assume correctly all in flight requests are flushed after
return from this uAPI call? Or some of pending requests may be subject
to loss or failure? How does the caller/user specify these various
options (if there are) for device stop?
BTW, it would be nice to add the corresponding support to vdpa_sim_blk
as well to demo the stop handling. To just show it on vdpa-sim-net IMHO
is perhaps not so convincing.
-Siwei
* @get_config_size: Get the size of the configuration space includes
* fields that are conditional on feature bits.
* @vdev: vdpa device
@@ -316,6 +321,7 @@ struct vdpa_config_ops {
u8 (*get_status)(struct vdpa_device *vdev);
void (*set_status)(struct vdpa_device *vdev, u8 status);
int (*reset)(struct vdpa_device *vdev);
+ int (*stop)(struct vdpa_device *vdev, bool stop);
size_t (*get_config_size)(struct vdpa_device *vdev);
void (*get_config)(struct vdpa_device *vdev, unsigned int offset,
void *buf, unsigned int len);
