Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API

[Gerd Hoffmann <kraxel@redhat.com>]

Avi Kivity wrote:
>>
>> Grant handles should be handled by a different API.
> 
> That was terse... here's how I think it should be done:
> 
> - step 1: map the grant handle into guest physical memory

Haha.

Guess I should explain a bit more what grant handles are ...

A xen domain can give other domains permission to map specific pages.
This is called a grant.  This is used by xen paravirtual drivers.  The
domU frontend driver hands out grants to the backend driver (usually
dom0), so the backend driver can fill the guest buffers with the data.

I want qemu be able to handle the backend side, so it must be able to
map and unmap grants.   I think fitting this into the memory mapping API
can be useful, especially if the mapping API starts to get used by
generic code.  Maybe the block layer some day accepts iovecs with guest
physical addresses and does map/unmap transparently?  Then I'd like to
be able to pass in a iovec with grants instead.

cheers,
  Gerd