Re: [PATCH v6 0/4] Add support to enable/disable hotplug on pci-root controller

changelog: v6: incorporated Jan's suggestions. v5: incorporated suggestions from Laine for patches #2 and #3. The qemu command line is now added in a new function and called from qemuBuildControllersByTypeCommandLine(). Output xmls are now symlinked to input xmls for unit tests. v4: split the original patchset into a pci-root controller specific patch series. also the libvirt conf is now a sub-element of the pci-root controller as was suggested by Dan Berrange. Please see discussion here: https://listman.redhat.com/archives/libvir-list/2021-September/msg00839.html v3: reorganized the patches as per Laine's suggestion. Added more details in commit messages. Added conf description in formatdomain.rst. Added changelog for next release. v2: fixed bugs and added additional missing unit tests. v1: initial implementation. Had some bugs and missed some unit tests This patchset introduces libvirt xml support to enable/disable hotplug on the pci-root controller. It adds a 'target' subelement for the pci-root controller with a 'hotplug' property. This property can be used to enable or disable hotplug for the pci-root controller. For example, in order to disable hotplug on the pci-root controller, one has to use set '<target hotplug='off'>' as shown below: <controller type='pci' model='pci-root'> <target hotplug='off'/> </controller> '<target hotplug='on'>' option would enable hotplug for pci-root controller. This is also the default value. This option is only available for pc machine types and is applicable for qemu only/kvm accelerator onlt.This feature was introduced from qemu version 5.2 with the following change in qemu repository: 3d7e78aa7777f ("Introduce a new flag for i440fx to disable PCI hotplug on the root bus") The above qemu commit describes some reasons why users might to disable hotplug on PCI root buses [1]. The corresponding commandline option to qemu for x86 guests is: -global PIIX4_PM.acpi-root-pci-hotplug=<off/on> Notes: 1. The use case scenario described by Laine in https://listman.redhat.com/archives/libvir-list/2020-February/msg00110.html intentionally does not discuss i440fx and focusses solely on q35. I do realize that redhat has moved on from i440fx and currently efforts for new features are concentrated on q35 machines only. We have had some hard debates on this on the qemu mailing list before. The fact of the matter is that i440fx is not at 1-1 parity with q35. There are many users who are currenly using i440fx and are simply not ready to move to q35 without sacrificing some existing features they support today. For example https://wiki.qemu.org/images/4/4e/Q35.pdf lists some of q35 limitations. https://www.linux-kvm.org/images/0/06/2012-forum-Q35.pdf provides more information on the differences. Hence we need to solve the issue Laine has described in the above email for i440fx without adding additional bridges. Further, in Daniel Berrange's words from : https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg03012.html "From the upstream POV, there's been no decision / agreement to phase out PIIX, this is purely a RHEL downstream decision & plan. If other distros / users have a different POV, and find the feature useful, we should accept the patch if it meets the normal QEMU patch requirements. " Also to be noted that I have already experimented this qemu commandline option using libvirt passthrough feature as has been documented in http://blog.vmsplice.net/2011/04/how-to-pass-qemu-command-line-options.html This was only meant to be a short term solution until libvirt started supporting this natively. Supporting this option through libvirt would simplify their use case as well as add capability validations and graceful failure scenarios in case qemu did not support the option. Ani Sinha (4): qemu: capablities: detect presence of acpi-root-pci-hotplug for i440fx machines conf: introduce option to enable/disable pci hotplug on pci-root controller qemu: command: add support to enable/disable hotplug on pci-root controller NEWS: release note the new hotplug enable/disable option on pci-root controller NEWS.rst | 6 ++++ docs/formatdomain.rst | 12 ++++--- src/qemu/qemu_capabilities.c | 4 +++ src/qemu/qemu_capabilities.h | 3 ++ src/qemu/qemu_command.c | 17 ++++++++++ src/qemu/qemu_validate.c | 9 +++++- .../caps_5.2.0.x86_64.xml | 1 + .../caps_6.0.0.x86_64.xml | 1 + .../caps_6.1.0.x86_64.xml | 1 + .../pc-i440fx-acpi-root-hotplug-disable.args | 31 +++++++++++++++++++ .../pc-i440fx-acpi-root-hotplug-disable.err | 1 + .../pc-i440fx-acpi-root-hotplug-disable.xml | 30 ++++++++++++++++++ .../pc-i440fx-acpi-root-hotplug-enable.xml | 30 ++++++++++++++++++ tests/qemuxml2argvtest.c | 3 ++ .../pc-i440fx-acpi-root-hotplug-disable.xml | 1 + .../pc-i440fx-acpi-root-hotplug-enable.xml | 1 + tests/qemuxml2xmltest.c | 4 +++ 17 files changed, 149 insertions(+), 6 deletions(-) create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.args create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.err create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-disable.xml create mode 100644 tests/qemuxml2argvdata/pc-i440fx-acpi-root-hotplug-enable.xml create mode 120000 tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-disable.xml create mode 120000 tests/qemuxml2xmloutdata/pc-i440fx-acpi-root-hotplug-enable.xml