Re: virtq questions

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Oct 02, 2019 at 09:40:11AM +0200, Miklos Szeredi wrote:
> Looking at the ugly retry logic in virtiofs and have some questions.

Hi Miklos,

What are you thinking w.r.t cleanup of retry logic. As of now we put
requests in a list and retry later with the help of a worker.

Other option will probably be block the submitter if queue is full. Make
it sleep, wake up after a while and retry submission.

> First one is, where do these features come from:
> 
> VIRTIO_F_RING_PACKED
> VIRTIO_RING_F_INDIRECT_DESC

Looks like these feature bits are supposed to be advertised by the device
if device supports these capabilities.

I see in qemu code that bunch of drivers are advertisig this capability.
(virtio_scsi, virtio_blk etc).

> 
> I see that in virtiofs "packed" is off and "indirect" is on.  Is this
> guaranteed?

I can't find specifying any feature bits in vhost-user-fs.c. So we
probably are getting a default value.

Thanks
Vivek