[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH V7 1/2] libxl: Add support for Virtio disk configuration
On 27.04.22 10:27, Roger Pau Monné wrote: On Wed, Apr 27, 2022 at 11:20:04AM +0300, Oleksandr wrote:On 25.04.22 16:12, Roger Pau Monné wrote: Hello RogerOn Sat, Apr 23, 2022 at 10:39:14AM +0300, Oleksandr wrote:On 22.04.22 12:41, Roger Pau Monné wrote: Hello RogerOn Fri, Apr 08, 2022 at 09:21:04PM +0300, Oleksandr Tyshchenko wrote:From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx> --- a/docs/man/xl-disk-configuration.5.pod.in +++ b/docs/man/xl-disk-configuration.5.pod.in @@ -232,7 +232,7 @@ Specifies the backend implementation to use =item Supported values -phy, qdisk +phy, qdisk, other =item Mandatory @@ -244,11 +244,13 @@ Automatically determine which backend to use. =back -This does not affect the guest's view of the device. It controls -which software implementation of the Xen backend driver is used. +It controls which software implementation of the backend driver is used. +Depending on the "protocol" option this may affect the guest's view +of the device. Not all backend drivers support all combinations of other options. -For example, "phy" does not support formats other than "raw". +For example, "phy" and "other" do not support formats other than "raw" and +"other" does not support protocols other than "virtio-mmio". Normally this option should not be specified, in which case libxl will automatically determine the most suitable backend. @@ -344,8 +346,35 @@ can be used to disable "hole punching" for file based backends which were intentionally created non-sparse to avoid fragmentation of the file. +=item B<protocol>=I<PROTOCOL> + +=over 4 + +=item Description + +Specifies the communication protocol to use for the chosen "backendtype" option + +=item Supported values + +xen, virtio-mmioFrom a user PoV, I think it would be better to just select xen or virtio here, but not the underlying configuration mechanism used to expose the devices to the guest.I got your point.We would likely need to add a different option to select mmio or pci then, but that should be set by default based on architecture/guest type. For example on x86 it should default to pci, while on Arm I guess it will depend on whether the guest has PCI or not? In any case, I think we should offer an option that's selecting between xen or virtio protocol, and the way to expose the configuration of the device shouldn't need to be explicitly selected by the user.ok, for now I will use "xen and virtio" values for the "protocol" option, then internally toolstack will assume that "virtio" really means "virtio-mmio". When there is a need to expand that support to "virtio-pci", we will see how to deal with it from the configuration PoV, probably like you suggested above by adding another option (e.g. "transport") with default values based on the architecture/guest type.I think this likely also wants to be a separate field in libxl_device_disk, which could be left empty and libxl will attempt to set a default. For example have the following in libxl_types.idl: libxl_device_protocol = Enumeration("device_protocol", [ (0, "UNKNOWN"), (1, "XEN"), (2, "VIRTIO"), ]) libxl_device_configuration = Enumeration("device_configuration", [ (0, "UNKNOWN"), (1, "XENBUS"), (2, "MMIO"), ]) libxl_device_disk = Struct("device_disk", [ ("protocol", libxl_device_protocol), ("configuration", libxl_device_configuration), ]) I don't like libxl_device_configuration much, I think is too generic, but I can't think of anything better. Maybe others can provide better names.Here [1] we had a discussion regarding user configuration options. "protocol" cannot be used as it will lead to the confusion (at least with Xen PV block device which already has "protocol" frontend's entry in Xenstore). Preliminary, we had agreed on the following names: 1. specification: xen or virtio 2. transport: mmio or pci Please tell me, are you OK with them?Yes, that's fine. My main point is that libxl_device_disk should contain both fields, so a 3rd party toolstack can set 'specification = virtio' and let Xen decide the transport to use. I'm dubious whether we want to have a xenbus transport for xen specification to use, but I guess it's fine to say that for specification == xen transport is ignored. At least for now, I guess. It might be a thing in case someone decides to add argo support. Juergen Attachment:
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