On Tue, Jan 13, 2009 at 01:02:52PM +1030, Rusty Russell wrote: > On Friday 09 January 2009 08:21:27 Ira Snyder wrote: > > Rusty, since you wrote the virtio code, can you point me at the things I > > would need to implement to use virtio over the PCI bus. > > > > The guests (PowerPC computers running Linux) are PCI cards in the host > > system (an Intel Pentium3-M system). The guest computers can access all > > of the host's memory. The guests provide a 1MB (movable) window into > > their memory. > > > > The PowerPC computers also have a DMA controller, which I've used to get > > better throughput from my driver. I have a way to create interrupts to > > both the host and guest systems. > > > > I've read your paper titled: "virtio: Towards a De-Facto Standard For > > Virtual I/O Devices" > > > > If I read that correctly, then I should implement all of the functions > > in struct virtqueue_ops appropriately, and the existing virtio drivers > > should just work. The only concern I have there is how to make guest -> > > host transfer use the DMA controller. I've done all programming of it > > from the guest kernel, using the Linux DMAEngine API. > > Hi Ira, > > Interesting system: the guest being able to access the host's memory but > not (fully) vice-versa makes this a little different from the current > implementations where that was assumed. virtio assumes that the guest will > publish buffers and someone else (ie. the host) will access them. >
The guest system /could/ publish all of its RAM, but with 256MB per board, 19 boards per cPCI crate, that's way too much for a 32-bit PC to map into it's memory space. That's the real reason I use the 1MB windows. I could make them bigger (16MB would be fine, I think), but I doubt it would make much of a difference to the implementation. > > Are there any other implementations other than virtio_ring? > > There were some earlier implementations, but they were trivial. And not > particularly helpful in your case. > > In summary, yes, it should work quite nicely, but rather than publishing the > buffers to the host, the host will need to tell the guest where it wants them > transferred (possibly using that 1M window, and a notification mechanism). > That will be the complex part I think. > I've got a system like that right now in the driver that started this thread. I tried to mimic the buffer descriptor rings in a network card. The virtio system doesn't seem to be too different. I can probably work something out. What's keeping me from getting started is what to do with the virtqueue_ops structure once I've got the functions to fill it in. There isn't a register_virtqueue_ops() function. I'm not at all sure when to use a struct virtio_driver or a struct virtio_device. I hunch I need one of these. If I've understood this whole thing correctly, then I should be able to register a virtio_ops on both sides, and then insmod virtio_net and virtio_console, and have them "just work". I guess what I'm looking for is something trivial, something that'll insmod and printk() whenever one of the virtqueue_ops pointers is called. Something like a template. That's how I really learned when all of the uart functions are called, for example. Thanks, Ira _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
