On Wed, Apr 08, 2026 at 05:23:39PM +0000, Thierry Escande wrote: > This series adds support for a new 'hotplug' option for PCI devices to be > passthrough'd to guests. > > The current mechanism for device passthrough uses QMP device_add command > to hot-plug PCI devices to the guest Qemu instance. This is an issue for > guests running on Q35 chipset (preliminary support posted at [1]) since the > Q35 PCI root bus does not support hotplug. Devices could be hotplugged to > a secondary PCI bus but Xen only support 1 PCI bus for now. > > The 'hotplug' option allows to control how devices are attached to the > guest, either by using the legacy QMP mechanism (this is the default) or by > passing it directly to the Qemu command line using xen-pci-passthrough > device. > > Example usage in cfg file: > pci = [ "00:03.0,seize=1,hotplug=0" ] > > Since Qemu -device option accepts parameters in json format, this > patchset adds a new internal function libxl__device_pci_get_qmp_json() that > generates the device json object used for both QMP hotplug and command line > passing. > Also, the function libxl_pci_assignable() is made available from libxl.h > for access in libxl_dm.c. I don't know if it's ok to make it public or if > it should stay private. Maybe it should be renamed as > libxl_device_pci_assignable() to match the other PCI device APIs. > > This has been successfully tested on Xen 4.22-dev and Qemu 10.0 running > Debian VMs in both Bios and UEFI mode with a passthrough'd nvme disk. > Disabling the hotplug mechanism might be made mandatory for Q35 machines > later, once Q35 support is merged upstream.
Generally I like the approach, and it looks sensible on the first look. But CI says it fails to build: https://gitlab.com/xen-project/people/marmarek/xen/-/pipelines/2439831766 -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab
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