[RFC proxmox-perl-rs/qemu-server/qemu-server-rs 0/9] pci-handling rewrite (part 1)

[Dominik Csapak <d.csapak@proxmox.com>]

# Motivation

We want to extend the PCI layout mechanism to be easily extendable, especially
for NUMA awareness and replicating host-toplogy (e.g. see bug #7283 [0]).

This is necessary for some performance gains in guests, especially with
high-end hardware where users pay extra for higher performance.

# The Problem

PCI addresses (and hardware layout in general) must be fixed for our qemu
guests, since this is part of the machine state and must be stable for
live-migration suspend/resume, etc.

Currently, these addresses are hardcoded in perl hashes, with a long history of
devs (me included) piling onto new addresses on there, using whatever free
address there exists.

This lead to a very convoluted and scattered assignment list, without any
underlying structure, which makes it harder the more new devices are added.
(Using a wrong address only surfaces when running some tests or starting a
guest with it)

# My Proposed Solution

So to fix the current situation I propose a plan in multiple phases:

## Phase 1 - untangling perl code to rust (this series)

To extend/switch between multiple PCI layouts, we first must untangle the
current situation and make it easier to see what is actually used.

I did this in rust, by using the type system to represent the PCI layout, and
inferring the addresses from the layout, not the other way around.

That makes it easier to see where there is actually free space and where we can
add new things.

It also highlights how messy the current layout is. (See the legacy layout in
the `pve-qemu-server-pci` crate)

I also introduced here a generic `Machine` struct that's intended to hold
information useful to more call sites in contrast to passing a lot of arguments
everywhere, similar to the Cfg2Cmd class, but usable in the rust codebase.

## Phase 2 - extending pci layouts (partially this series)

This would introduce a new layout ("v2") that can be used in an opt-in manner,
and is vastly more logically constructed, which makes it easy to extend and
argue about. See the "preview" patch (last of pve-qemu-server-rs) for how this
layout can look like.

This part would also entail restructuring the addr calls in qemu-server's perl
code, so to only have a single entry point ("address" for example) instead of
splitting between 'print_pci_addr' and 'print_pcie_addr'.

In this phase we could also emit the commandline for devices that are currently
in the q35 config files read with readconfig.

## Phase 3 - more perl to rust code port

To better work with the layout, we'd need to pull more code from qemu-server
into rust, for this plan mostly from PCI.pm and USB.pm but maybe some other
helpers too (version comparsion comes to mind).

Here we could start using the schema from pve-api-types to parse e.g. the
config rust-side, but the schema still has to live perl side (ofc).

## Phase 4 - Host and NUMA layouts

With all the pieces in place, we can then easily extend the new layout by PCI
switches that are needed for assigning to NUMA nodes and replicating the host
toplogy for passed through devices.

# Notes

* pve-qemu-server-rs is a new git repo, but the crate in it could
  easily be integrated somewhere else. Having this as a separate repo
  could replace 'qemu-server' at one point though.
* This is an RFC, so comments about the general design/plan are desired.
* There are still some rough edges (e.g. hardcoding the perl config max values
  in rust again), but it should work as intended and it passes our qemu-server
  regression tests.
* Names and crate placement are not fixed, I know that some names I chose are
  not optimal, if you do have better names/places, please suggest them.
* I based this on my recent qemu-server hotplug series [1], so keep that in
  mind when testing/applying
* Opted to do this in rust for now, since I think that is the best way forward.
  If the consensus is to to the layouting changes in perl, or keep some parts in
  perl, that's fine with me too and I'll change my efforts accordingly

0: https://bugzilla.proxmox.com/show_bug.cgi?id=7283
1: https://lore.proxmox.com/pve-devel/20260914085725.1299009-1-d.csapak@proxmox.com/


pve-qemu-server-rs:

Dominik Csapak (4):
  add pve-qemu-server-pci crate for guest PCI address generation
  pci: add machine abstraction and PCI bridge generation
  pci: layout: add v2 PCI and PCIe layouts
  fixup! add pve-qemu-server-pci crate for guest PCI address generation


proxmox-perl-rs:

Dominik Csapak (2):
  pve: add bindings for `pve-qemu-server-pci` crate
  pve: pci bindings: add bindings for the `Machine` struct

 pve-rs/Cargo.toml                  |  1 +
 pve-rs/Makefile                    |  2 ++
 pve-rs/src/bindings/mod.rs         |  3 ++
 pve-rs/src/bindings/pci/machine.rs | 45 ++++++++++++++++++++++++++++
 pve-rs/src/bindings/pci/mod.rs     | 48 ++++++++++++++++++++++++++++++
 5 files changed, 99 insertions(+)
 create mode 100644 pve-rs/src/bindings/pci/machine.rs
 create mode 100644 pve-rs/src/bindings/pci/mod.rs


qemu-server:

Dominik Csapak (3):
  pci: use PVE::RS::PCI bindings
  helpers: factor out the version parts parsing
  pci: bridges: use the rust `Machine` struct to pass parameters

 src/PVE/QemuServer.pm                    |   4 +-
 src/PVE/QemuServer/Helpers.pm            |  22 +-
 src/PVE/QemuServer/PCI.pm                | 296 +++--------------------
 src/test/Makefile                        |   5 +-
 src/test/TestsCommon/CommandLineMocks.pm |   3 +
 src/test/run_pci_addr_checks.pl          | 141 -----------
 6 files changed, 56 insertions(+), 415 deletions(-)
 delete mode 100755 src/test/run_pci_addr_checks.pl


Summary over all repositories:
  11 files changed, 155 insertions(+), 415 deletions(-)

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