[Qemu-devel] Re: [PATCH 0/2 version 2] fw_cfg: Implement fast "DMA"-type operation for rapidly copying in kernel, initrd [etc] into the guest

[Gleb Natapov]

On Mon, Jul 19, 2010 at 11:49:09AM +0100, Richard W.M. Jones wrote:
> On Mon, Jul 19, 2010 at 01:45:00PM +0300, Gleb Natapov wrote:
> > On Mon, Jul 19, 2010 at 11:15:04AM +0100, Richard W.M. Jones wrote:
> > > 
> > > This is the second version of the patch.
> > > 
> > > We don't use the word "blit" any more, instead this is replaced with
> > > "DMA", even though it's not quite like a DMA operation on physical
> > > hardware.
> > > 
> > You ignored the whole discussion above. Calling things DMA will not make
> > them so. You haven't event implemented Alexander's suggestion to poll
> > for DMA completion which will at lease make the interface to the guest
> > palatable.
> 
> I read everything in the discussion.
> 
> I can add polling however.
> 
If copying (call to cpu_physical_memory_write()) really takes 6 or more
seconds we should really make it async from the beginning. (If we are going
this way at all. I prefer to use virtio-serial for such complex gust/host
communication. fw_cfg was designed to be simple at should stay so. And
it is used by other arches too so any extension should be usable there).

--
                        Gleb.