On 19.07.2010, at 11:00, Gleb Natapov wrote: > On Mon, Jul 19, 2010 at 10:54:43AM +0200, Alexander Graf wrote: >> >> On 19.07.2010, at 10:48, Gleb Natapov wrote: >> >>> >>>> Were there DMA capable devices back in ISA times? There must be. If so, we >>>> can just take a look at what they do and do it similarly. Bus mastering >>>> was a new thing for PCI, right? >>>> >>> I think IDE can be considered DMA capable ISA device, no? At least >>> it works by writing to PIO ports and getting result into memory, but >>> with interrupts and status bits and everything that real device should >>> have. On board DMA engine is also ISA device. >> >> We could define our device to be polling. So all we need is a status bit >> that the guest sets when it starts the DMA and the device unsets when the >> DMA is done. In our case that should be immediate, because the PIO invokes >> the full code paths, but it would look more like a real device, no? >> > This is better, but it shouldn't be synchronous. Kernel and initrd are > on disk so why not setup aio and read them from io thread allowing vcpu > thread immediately return to guest mode to process interrupts.
That would work with the above described device model. If we're going synchronous or asynchronous would become an implementation detail. > Or why > not use virtio-serial while we are at it? After all virtio-serial is > there to allow host and guest communication. Because virtio-serial needs us to set up the full virtio-pci stack. That's too much to mess with in an option rom IMHO. Alex
