Re: [Qemu-devel] RFC: guest-side retrieval of fw_cfg file

[Michael S. Tsirkin]

On Wed, Jul 15, 2015 at 06:01:42PM +0200, Igor Mammedov wrote:
> On Wed, 15 Jul 2015 17:08:27 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Mon, Jul 13, 2015 at 04:09:37PM -0400, Gabriel L. Somlo wrote:
> > > Hi,
> > > 
> > > A while ago I was pondering on the options available for retrieving
> > > a fw_cfg blob from the guest-side (now that we can insert fw_cfg
> > > files on the host-side command line, see commit 81b2b8106).
> > > 
> > > So over the last couple of weekends I cooked up the sysfs kernel
> > > module below, which lists all fw_cfg files
> > > under /sys/firmware/fw_cfg/<filename>.
> > 
> > One concern here is that there will be a conflict here if fw cfg
> > is used by ACPI. I don't know whether that last is a good idea
> > though, so maybe not a real concern. I think Igor
> > wanted to make it so.
> 
> I don't see any conflict here so far, it's just guest side module that
> accesses fw_cfg.

If there's ACPI code that accesses fw_cfg in response to an interrupt,
it'll race with fw cfg access by guest OS. On linux we might be able to
block ACPI preventing it from running. We probably won't be able to do
it on windows.

-- 
MST