[RFC PATCH v3 0/3] xl: Allow PCI devices to be passthrough'd via Qemu command line

["Thierry Escande" <thierry.escande@xxxxxxxxxx>]

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, to handle the assignable PCI device list, the function
libxl_pci_assignable() is renamed as libxl_device_pci_assignable() and is
made available from libxl.h for access in libxl_dm.c. 2 other functions are
also exported internally: libxl__pciback_dev_is_assigned() and
libxl__device_pci_assignable_add().

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.

[1] 
https://lore.kernel.org/xen-devel/20260313163455.790692-1-thierry.escande@xxxxxxxxxx/

Changes in v2:
- Add support for YAJL json parser

Changes in v3:
- Move code block of device command line parameters creation
- Better handling of pci device assignation

Thierry Escande (3):
  xl: Add pci device hotplug option
  libxl: Allow PCI device passthrough using -device Qemu command line
  docs: provide description for pci hotplug option

 docs/man/xl-pci-configuration.5.pod | 17 ++++++
 docs/man/xl.cfg.5.pod.in            |  6 ++
 tools/include/libxl.h               |  1 +
 tools/libs/light/libxl_dm.c         | 85 +++++++++++++++++++++++++++++
 tools/libs/light/libxl_internal.h   |  7 +++
 tools/libs/light/libxl_pci.c        | 57 +++++++++++++------
 tools/libs/light/libxl_types.idl    |  1 +
 tools/libs/util/libxlu_pci.c        |  2 +
 tools/xl/xl_parse.c                 |  5 ++
 9 files changed, 163 insertions(+), 18 deletions(-)

-- 
2.53.0



--
Thierry Escande | Vates XCP-ng Developer

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