On Fri, 2013-05-31 at 12:41 +0200, Paolo Bonzini wrote:
> It may be halfway through, but it is always restarted on the destination.
"restarted" as in the whole transfer is restarted if any right ? So we
can essentially consider as a new request for which we just did
scsi_req_enqueue() ?
IE. We don't do direct DMA to guest pages just yet (we still do copies)
so basically our process is:
1- Obtain request from guest
2- Queue it (scsi_req_enqueue)
3- No transfer -> go away (completion is called)
4- Pre-process user descriptors (check desc type direct vs indirect,
position our "cursor" walking them etc....)
5- scsi_req_continue()
.../... loop of callbacks & transfer
Now from what you say, I assume that regardless of the point where
the request was, when we "resume" it will always be at step 4 ?
IE. I can just pre-process the descriptors again ? (I actually need
to transfer them again from the guest since I suspect I clobber them
at the very least due to byteswap) and call scsi_req_continue() and
assume the transfer (if any) started from the beginning ?
> virtio-scsi parses the whole descriptor chain upfront and sends the
> guest addresses in the migration stream.
>
> > Is not it the same QEMU thread which handles hcalls and QEMU console
> > commands so the migration cannot stop parsing/handling a vscsi_req?
>
> The VM is paused and I/O is flushed at the point when the reqs are sent.
> That's why you couldn't get a pending request. Only failed requests
> remain in queue.
Ben.
