Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework

[David Gibson]

On Fri, Nov 11, 2011 at 03:10:56PM -0700, Alex Williamson wrote:
> Thanks Konrad!  Comments inline.
> On Fri, 2011-11-11 at 12:51 -0500, Konrad Rzeszutek Wilk wrote:
> > On Thu, Nov 03, 2011 at 02:12:24PM -0600, Alex Williamson wrote:
[snip]
> > > +The GET_NUM_REGIONS ioctl tells us how many regions the device supports:
> > > +
> > > +#define VFIO_DEVICE_GET_NUM_REGIONS     _IOR(';', 109, int)
> > 
> > Don't want __u32?
> 
> It could be, not sure if it buys us anything maybe even restricts us.
> We likely don't need 2^32 regions (famous last words?), so we could
> later define <0 to something?

As a rule, it's best to use explicit fixed width types for all ioctl()
arguments, to avoid compat hell for 32-bit userland on 64-bit kernel
setups.

[snip]
> > > +Again, zero count entries are allowed (vfio-pci uses a static interrupt
> > > +type to index mapping).
> > 
> > I am not really sure what that means.
> 
> This is so PCI can expose:
> 
> enum {
>         VFIO_PCI_INTX_IRQ_INDEX,
>         VFIO_PCI_MSI_IRQ_INDEX,
>         VFIO_PCI_MSIX_IRQ_INDEX,
>         VFIO_PCI_NUM_IRQS
> };
> 
> So like regions it always exposes 3 IRQ indexes where count=0 if the
> device doesn't actually support that type of interrupt.  I just want to
> spell out that bus drivers have this kind of flexibility.

I knew what you were aiming for, so I could see what you meant here,
but I don't think the doco is very clearly expressed at all.

-- 
David Gibson                    | I'll have my music baroque, and my code
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                                | _way_ _around_!
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