On Fri, 21 Oct 2016 02:44:37 +0530
Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> On 10/21/2016 2:35 AM, Alex Williamson wrote:
> > On Fri, 21 Oct 2016 01:59:55 +0530
> > Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> >
> >> On 10/21/2016 1:04 AM, Alex Williamson wrote:
> >>> On Tue, 18 Oct 2016 02:52:10 +0530
> >>> Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> >>>
> >>>> Function vfio_device_api_string() returns string based on flag set in
> >>>> vfio_device_info's flag. This should be used by vendor driver to get string
> >>>> based on flag for device_api attribute.
> >>>>
> >>>> Signed-off-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
> >>>> Signed-off-by: Neo Jia <cjia@xxxxxxxxxx>
> >>>> Change-Id: I42d29f475f02a7132ce13297fbf2b48f1da10995
> >>>> ---
> >>>> drivers/vfio/vfio.c | 15 +++++++++++++++
> >>>> include/linux/vfio.h | 2 ++
> >>>> 2 files changed, 17 insertions(+)
> >>>>
> >>>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> >>>> index 10ef1c5fa762..aec470454a13 100644
> >>>> --- a/drivers/vfio/vfio.c
> >>>> +++ b/drivers/vfio/vfio.c
> >>>> @@ -1917,6 +1917,21 @@ int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, int num_irqs,
> >>>> }
> >>>> EXPORT_SYMBOL(vfio_set_irqs_validate_and_prepare);
> >>>>
> >>>> +const char *vfio_device_api_string(u32 flags)
> >>>> +{
> >>>> + if (flags & VFIO_DEVICE_FLAGS_PCI)
> >>>> + return "vfio-pci";
> >>>> +
> >>>> + if (flags & VFIO_DEVICE_FLAGS_PLATFORM)
> >>>> + return "vfio-platform";
> >>>> +
> >>>> + if (flags & VFIO_DEVICE_FLAGS_AMBA)
> >>>> + return "vfio-amba";
> >>>> +
> >>>> + return "";
> >>>> +}
> >>>> +EXPORT_SYMBOL(vfio_device_api_string);
> >>>> +
> >>>> /*
> >>>> * Pin a set of guest PFNs and return their associated host PFNs for local
> >>>> * domain only.
> >>>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> >>>> index 31d059f1649b..fca2bf23c4f1 100644
> >>>> --- a/include/linux/vfio.h
> >>>> +++ b/include/linux/vfio.h
> >>>> @@ -116,6 +116,8 @@ extern int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr,
> >>>> int num_irqs, int max_irq_type,
> >>>> size_t *data_size);
> >>>>
> >>>> +extern const char *vfio_device_api_string(u32 flags);
> >>>> +
> >>>> struct pci_dev;
> >>>> #ifdef CONFIG_EEH
> >>>> extern void vfio_spapr_pci_eeh_open(struct pci_dev *pdev);
> >>>
> >>> Couldn't this simply be a #define in the uapi header?
> >>>
> >>> #define VFIO_DEVICE_PCI_API_STRING "vfio-pci"
> >>>
> >>> I don't really see why we need a lookup function.
> >>>
> >>
> >> String is tightly coupled with the FLAG, right?
> >> Instead user need to take care of making sure to return proper string,
> >> and don't mis-match the string, I think having function is easier.
> >
> > That's exactly why I proposed putting the #define string in the uapi,
> > by that I mean the vfio uapi header. That keeps the tight coupling to
> > the flag, they're both defined in the same place, plus it gives
> > userspace a reference so they're not just inventing a string to compare
> > against. IOW, the vendor driver simply does an sprintf of
> > VFIO_DEVICE_PCI_API_STRING and userspace (ie. libvirt) can do a strcmp
> > with VFIO_DEVICE_PCI_API_STRING from the same header and everybody
> > arrives at the same result.
> >
> >> Vendor driver should decide the type of device they want to expose and
> >> set the flag, using this function vendor driver would return string
> >> which is based on flag they set.
> >
> > Being a function adds no intrinsic value and being in a uapi header does
> > add value to userspace. Thanks,
> >
>
> Ok. The strings should be in uapi, but having function (like below) to
> return proper string based on flag would be good to have for vendor driver.
>
> +const char *vfio_device_api_string(u32 flags)
> +{
> + if (flags & VFIO_DEVICE_FLAGS_PCI)
> + return VFIO_DEVICE_API_PCI_STRING;
> +
> + if (flags & VFIO_DEVICE_FLAGS_PLATFORM)
> + return VFIO_DEVICE_API_PLATFORM_STRING;
> +
> + if (flags & VFIO_DEVICE_FLAGS_AMBA)
> + return VFIO_DEVICE_API_AMBA_STRING;
> +
> + return "";
> +}
> +EXPORT_SYMBOL(vfio_device_api_string);
I disagree, it's pointless maintenance overhead. It's yet another
function that we need to care about for kABI and it offers almost no
value. Thanks,
Alex
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