linux-kernel - Re: [RFC PATCH 15/21] PCI: Make PCI saved state and capability structs public

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Message-ID: <CALzav=eO4Lc15NV5fh-=LCaXz+s4-5+UxPLC4ePMqwUatvLXtw@mail.gmail.com>
Date: Wed, 22 Oct 2025 10:45:31 -0700
From: David Matlack <dmatlack@...gle.com>
To: Vipin Sharma <vipinsh@...gle.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, Lukas Wunner <lukas@...ner.de>, bhelgaas@...gle.com, 
	alex.williamson@...hat.com, pasha.tatashin@...een.com, graf@...zon.com, 
	pratyush@...nel.org, gregkh@...uxfoundation.org, chrisl@...nel.org, 
	rppt@...nel.org, skhawaja@...gle.com, parav@...dia.com, saeedm@...dia.com, 
	kevin.tian@...el.com, jrhilke@...gle.com, david@...hat.com, 
	jgowans@...zon.com, dwmw2@...radead.org, epetron@...zon.de, 
	junaids@...gle.com, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 15/21] PCI: Make PCI saved state and capability
 structs public

On Mon, Oct 20, 2025 at 4:49 PM Vipin Sharma <vipinsh@...gle.com> wrote:
>
> On 2025-10-18 20:11:26, Jason Gunthorpe wrote:
> > On Sat, Oct 18, 2025 at 03:36:20PM -0700, Vipin Sharma wrote:
> >
> > > Having __packed in my version of struct, I can build validation like
> > > hardcoded offset of members. I can add version number (not added in this
> > > series) for checking compatbility in the struct for serialization and
> > > deserialization. Overall, it is providing some freedom to how to pass
> > > data to next kernel without changing or modifying the PCI state
> > > structs.
> >
> > I keep saying this, and this series really strongly shows why, we need
> > to have a dedicated header directroy for LUO "ABI" structs. Putting
> > this random struct in some random header and then declaring it is part
> > of the luo ABI is really bad.
>
> Now that we have PCI, IOMMU, and VFIO series out. What should be the
> strategy for LUO "ABI" structs? I would like some more clarity on how
> you are visioning this.
>
> Are you suggesting that each subsystem create a separate header file for
> their serialization structs or we can have one common header file used
> by all subsystems as dumping ground for their structs?

I think we should have multiple header files in one directory, that
way we can assign separate MAINTAINERS for each file as needed.

Jason Miu proposed the first such header for KHO in
https://lore.kernel.org/lkml/CALzav=eqwTdzFhZLi_mWWXGuDBRwWQdBxQrzr4tN28ag8Zr_8Q@mail.gmail.com/.

Following that example we can add vfio_pci.h and pci.h to that
directory for VFIO and PCI ABI structs respectively.