[libvirt RFCv11 00/33] multifd save restore prototype

[Daniel P. Berrangé]

On Mon, Oct 23, 2023 at 04:06:53PM +0200, Claudio Fontana wrote:
> On 10/11/23 17:29, Daniel P. Berrangé wrote:
> > On Wed, Oct 11, 2023 at 04:56:12PM +0200, Claudio Fontana wrote:
> >>
> >> On 10/11/23 16:05, Daniel P. Berrangé wrote:
> >>>
> >>> Instead of using 'getfd' though we have to use 'add-fd'.
> >>>
> >>> Anyway, this lets us do FD passing as normal, whle also
> >>> letting us specify the offset.
> >>>
> >>>  {"execute": "add-fd", "arguments": {"fdset-id":"migrate"}}
> >>>  {"execute": "migrate", "arguments": {"detach":true,"blk":false,"inc":false,"uri":"file:/dev/fdset/migrate,offset=124456"}}'
> 
> 
> Hi Daniel,
> 
> the "add-fd" is the part that I don't understand at all,
> 
> should we actually pass an fd there like with fd-get, already open with the savevm file?
> Something in pseudocode like:
> 
> virsh qemu-monitor-command --pass-fds 10 --cmd='{"execute": "add-fd", "arguments": {"fdset-id":10}} ?
> 
> should we use "opaque" instead of "fdset-id" if you want to actually set it to "migrate"?
> And how to reference it later?
> 
> virsh qemu-monitor-command --cmd='{"execute": "migrate", "arguments": {"detach":true,"blk":false,"inc":false,"uri":"file:/dev/fdset/migrate,offset=124456"}}
> 
> ?
> 
> "opaque" does not seem to get me a reachable /dev/fdset/migrate though.
> 
> I can currently trigger the migration to the URI file:/mnt/nvme/savevm so that seems to work fine,
> it's the file:/dev/fdset part that I am still unable to glue together.

Sorry, I was mis-remembering the fdset usage.  They have to be used via
a numeric ID value, not a named set. The numeric IDs don't match the FD
numbers either. So I think it would be :

 virsh qemu-monitor-command --pass-fds 10 --cmd='{"execute": "add-fd", "arguments": {"fdset-id":7}} ? 
 virsh qemu-monitor-command --cmd='{"execute": "migrate", "arguments": {"detach":true,"blk":false,"inc":false,"uri":"file:/dev/fdset/7,offset=124456"}}
 

With regards,
Daniel
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