Re: [Qemu-devel] [RFC PATCH V2 02/10] Qemu/VFIO: Add new VFIO_GET_PCI_CAP_INFO ioctl cmd definition

[Alex Williamson]

On Tue, 2015-11-24 at 21:35 +0800, Lan Tianyu wrote:
> Signed-off-by: Lan Tianyu <address@hidden>
> ---
>  linux-headers/linux/vfio.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
> index 0508d0b..732b0bd 100644
> --- a/linux-headers/linux/vfio.h
> +++ b/linux-headers/linux/vfio.h
> @@ -495,6 +495,22 @@ struct vfio_eeh_pe_op {
>  
>  #define VFIO_EEH_PE_OP                       _IO(VFIO_TYPE, VFIO_BASE + 21)
>  
> +
> +#define VFIO_FIND_FREE_PCI_CONFIG_REG   _IO(VFIO_TYPE, VFIO_BASE + 22)
> +
> +#define VFIO_GET_PCI_CAP_INFO   _IO(VFIO_TYPE, VFIO_BASE + 22)
> +
> +struct vfio_pci_cap_info {
> +    __u32 argsz;
> +    __u32 flags;
> +#define VFIO_PCI_CAP_GET_SIZE (1 << 0)
> +#define VFIO_PCI_CAP_GET_FREE_REGION (1 << 1)
> +    __u32 index;
> +    __u32 offset;
> +    __u32 size;
> +    __u8 cap;
> +};
> +
>  /* ***************************************************************** */
>  
>  #endif /* VFIO_H */

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?  These seem
like pointless ioctls, we're creating a purely virtual PCI capability,
the kernel doesn't really need to participate in that.  Also, why are we
restricting ourselves to standard capabilities?  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,

Alex