Re: [Qemu-devel] [PATCH 0/5] pc: make ROMs resizeable

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 19, 2014 at 09:16:09AM +0100, Markus Armbruster wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> 
> > On Tue, Nov 18, 2014 at 03:47:16PM +0100, Markus Armbruster wrote:
> >> "Michael S. Tsirkin" <mst@redhat.com> writes:
> >> 
> >> > At the moment we migrate ROMs which reside in fw cfg, which allows
> >> > changing ROM code at will, and supports migrating largish blocks early,
> >> > with good performance.
> >> > However, we are running into a problem: changing size breaks
> >> > migration every time.
> >> 
> >> Pardon my ignorance... changing ROM in migration?  I would expect
> >> migration to be as transparent for ROM as it is for RAM.  What am I
> >> missing?
> >> 
> >> [...]
> >
> > Nothing really.
> >
> > We migrate RAM size too - but if there's a mismatch, migration fails.
> >
> > RAM size is user configurable.
> >
> > ROM is used internally so we have to figure out the size,
> > and it turned out to be a hard problem, so we end up maintaining
> > logic for ROM size "like we did in 1.7" "like we did in 2.0" etc.
> >
> > I don't want to add any more: let's just accept whatever is migrated,
> > and stick to it.
> 
> Are you proposing to change ROM size on the target from "whatever was
> configured during startup" to "whatever is configured on the source"?

Exactly.  ROMs are running within guest, they should just migrate
together with VM. *They already do* except for their size.
Which kind of mostly does not create problems anyway because we round size up.


-- 
MST