Re: [PATCH 1/3] shared-mem: introduce page alignment restrictions

Michael S. Tsirkin
2025-03-04T10:52:57Z

On Sun, Feb 23, 2025 at 05:21:00AM +0000, Parav Pandit wrote:
> Overall extending pci cap structure is not good idea even though it may appear as small change for below reasons.
>
> 1. PCI spec already ran out of total bytes that can be stored in the capability section. Extending it will not help.
> A virtio level extended capability is not good either due to below guidance from PCI-SIG.
>
> 2. PCI spec highly discouraged putting vendor specific bits like this in the capability section.
> Citation: "It is strongly recommended that PCI Express devices place no registers in Configuration Space other than those in
> headers or Capability structures architected by applicable PCI specifications."

We can argue about new capabilities, but this is not doing it - it is
merely extending the existing one.

So I do not really get any of these arguments.

I'd be open to an alternative way to discover capabilities, as long as
we don't do that, I don't really see a reason to block minor tweaks
like this one.

At the same time, I am not sure why this is a capability at all.
why not in config space?

--
MST