[Qemu-devel] Re: [PATCHv2 1/3] pci: prepare irq code for interrupt state

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

On Thu, Nov 26, 2009 at 07:54:43PM +0100, Juan Quintela wrote:
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > This rearranges code in preparation for interrupt state
> > implementation.
> > Changes:
> > 	- split up but walk away from interrupt handling
> >           into a subroutine
> > 	- change irq_state from an array to bitmask
> > 	- verify that irq_state values are 0 or 1 on load
> >
> > There are no functional changes.
> 
> I guess that there is a good reason for changing for an array of ints to
> one bitmap.
> 
> Change looks ok, and if it worked for you, it should work for everybody
> (if you breaks pci_device migration stops working).

Works fine for me.

> I would delay changing things to bitmaps until we decide how to
> implement bitmaps in qemu (there are more than one implementation), at
> least:
>    - use array of ints, save as array of ints (i.e. works between hosts with
>      different endianess)
>    - use arraf of ints but save as array of bytes (break when you change
>      endianess)
>    - Now, you have a bitmap that fits in an uint8_t.
> 
> An probably some other way that I have missed.
> 
> Later, Juan.

As we have to preserve compatibility with old qemu, there's no choice
but to keep saving pci in the same way as we have done in the past: ints
in big endian format.  And forcing implementation to match the save
format is just silly.

So I think the best way forward is to apply this patch, then you as
vmstate expert can go and unify things.  My idea is that vmstate should
"conversion routines" which would e.g. convert bitmap to array of ints,
vmstate then saves ints.

-- 
MST