On 12/3/2015 6:25 AM, Alex Williamson wrote:
I didn't seen a matching kernel patch series for this, but why is the
kernel more capable of doing this than userspace is already?
The following link is the kernel patch.

These seem
like pointless ioctls, we're creating a purely virtual PCI capability,
the kernel doesn't really need to participate in that.

VFIO kernel driver has pci_config_map which indicates the PCI capability position and length which helps to find free PCI config regs. Qemu side doesn't have such info and can't get the exact table size of PCI capability. If we want to add such support in the Qemu, needs duplicates a lot of code of vfio_pci_configs.c in the Qemu.

Also, why are we
restricting ourselves to standard capabilities?

This version is to check whether it's on the right way and We can extend
this to pci extended capability later.

That's often a crowded
space and we can't always know whether an area is free or not based only
on it being covered by a capability.  Some capabilities can also appear
more than once, so there's context that isn't being passed to the kernel
here.  Thanks,

The region outside of PCI capability are not passed to kernel or used by Qemu for MSI/MSIX . It's possible to use these places for new capability. One concerns is that guest driver may abuse them and quirk of masking some special regs outside of capability maybe helpful.

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