Re: [Qemu-devel] [PATCH v4 1/1] vhost user: add support of live migration

[Paolo Bonzini]

> > Do you know the size of the ram_addr_t space from
> > VHOST_USER_SET_MEM_TABLE's user address and size fields?
> 
> For some reason, vhost_get_log_size() also takes pc-bios region. I
> think it's quite unnecessary given that the backend will not have
> access to this region.

That's by design.  The pc-bios is mapped into the guest memory, so it
is taken into account.  It shouldn't be a problem, it's just wasting
memory for <4GB VMs but it's not more expensive at run time.

> get_log_size() also computes the size of the rings, I wonder if it's
> necessary since the dev->mem->regions should already contain the
> rings, isn't it?

Indeed.

> > If the size isn't needed, you can reuse LOG_BASE, ignoring the content
> > of the payload and adding the SCM_RIGHTS file descriptor.
> 
> That's possible, if we assume that existing backends won't leak the
> passed fds (vapp does for ex), perhaps it needs a new flag (vhost-user
> features flags are common with vhost, not sure we want to add that
> here, but where else)

Ok, that's for mst to answer.  I think the leak wouldn't be too bad
because right now vhost-user live migration corrupts data so nobody
must be using it.  But if you want to introduce a new message, that
would also be okay of course.

Paolo