> On 17 Jun 2022, at 17:14, Oleksandr Tyshchenko <[email protected]> wrote: > > From: Oleksandr Tyshchenko <[email protected]> > > This patch adds basic support for configuring and assisting virtio-mmio > based virtio-disk backend (emulator) which is intended to run out of > Qemu and could be run in any domain. > Although the Virtio block device is quite different from traditional > Xen PV block device (vbd) from the toolstack's point of view: > - as the frontend is virtio-blk which is not a Xenbus driver, nothing > written to Xenstore are fetched by the frontend currently ("vdev" > is not passed to the frontend). But this might need to be revised > in future, so frontend data might be written to Xenstore in order to > support hotplugging virtio devices or passing the backend domain id > on arch where the device-tree is not available. > - the ring-ref/event-channel are not used for the backend<->frontend > communication, the proposed IPC for Virtio is IOREQ/DM > it is still a "block device" and ought to be integrated in existing > "disk" handling. So, re-use (and adapt) "disk" parsing/configuration > logic to deal with Virtio devices as well. > > For the immediate purpose and an ability to extend that support for > other use-cases in future (Qemu, virtio-pci, etc) perform the following > actions: > - Add new disk backend type (LIBXL_DISK_BACKEND_OTHER) and reflect > that in the configuration > - Introduce new disk "specification" and "transport" fields to struct > libxl_device_disk. Both are written to the Xenstore. The transport > field is only used for the specification "virtio" and it assumes > only "mmio" value for now. > - Introduce new "specification" option with "xen" communication > protocol being default value. > - Add new device kind (LIBXL__DEVICE_KIND_VIRTIO_DISK) as current > one (LIBXL__DEVICE_KIND_VBD) doesn't fit into Virtio disk model > > An example of domain configuration for Virtio disk: > disk = [ 'phy:/dev/mmcblk0p3, xvda1, backendtype=other, specification=virtio'] > > Nothing has changed for default Xen disk configuration. > > Please note, this patch is not enough for virtio-disk to work > on Xen (Arm), as for every Virtio device (including disk) we need > to allocate Virtio MMIO params (IRQ and memory region) and pass > them to the backend, also update Guest device-tree. The subsequent > patch will add these missing bits. For the current patch, > the default "irq" and "base" are just written to the Xenstore. > This is not an ideal splitting, but this way we avoid breaking > the bisectability. > > Signed-off-by: Oleksandr Tyshchenko <[email protected]>
OK, I am *really* sorry for coming in here at the last minute and quibbling about things. But this introduces a public interface which looks really wrong to me. I’ve replied to the mail from December where Juergen proposed the “Other” protocol. Hopefully this will be a simple matter of finding a better name than “other”. (Or you guys convincing me that “other” is really the best name for this value; or even Anthony asserting his right as a maintainer to overrule my objection if he thinks I’m out of line.) FWIW the Golang changes look fine. -George
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