Re: [Qemu-devel] [PATCH] virtio-pci: Set the QEMU_PCI_CAP_EXPRESS capability early in its DeviceClass realize method

[Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>]

Hi,

On Wed, 2 Dec 2015 11:51:46 +0200, marcel@redhat.com wrote:
> 2. We still have pci_is_express returning true, this is error prone because
> one can use this function assuming the device is express. Maybe we should
> call it "can_be_express" ?
> 
> If you think this is good enough, you can simply do the same:
>    - Instead of replacing the realize method, just advertise it with
>      "is_express" (meaning it can be express)
>    - Leave all the conditions as they were in prev patch.
> As a result, the pci config space will have the right length.

Oh but we can't do so, as the change of config space size is guest
visible and breaks migration; it must depend on your x-pcie-disable
flag :)

As I can't decide what's better, I'm following your initial suggestion
and submit for maintainers to review.

However, do note that there are few more evidence that 'pci_is_express'
is true while not necessarily placed on a pcie bus:
- pcie_endpoint_cap_init:
  it tests for 'pci_bus_is_express' although 'dev' is guaranteed to be
  'pci_is_express' (assertion in pcie_cap_init)
- 058fdcf 'xhci: add endpoint cap on express bus only'

Thanks,
Shmulik