Re: [RFC v2] PCI: sysfs per device SRIOV control and status

[Alexander Duyck <alexander.duyck@gmail.com>]

On 10/4/2012 3:14 PM, Donald Dutile wrote:
> Provide files under sysfs to determine the max number of vfs
> an SRIOV-capable PCIe device supports, and methods to enable and
> disable the vfs on a per device basis.
>
> Currently, VF enablement by SRIOV-capable PCIe devices is done
> in driver-specific module parameters.  If not setup in modprobe files,
> it requires admin to unload & reload PF drivers with number of desired
> VFs to enable.  Additionally, the enablement is system wide: all
> devices controlled by the same driver have the same number of VFs
> enabled.  Although the latter is probably desired, there are PCI
> configurations setup by system BIOS that may not enable that to occur.
>
> Three files are created if a PCIe device has SRIOV support:
> sriov_max_vfs -- cat-ing this file returns the maximum number
>                   of VFs a PCIe device supports.
> sriov_enable_vfs -- echo'ing a number to this file enables this
>                      number of VFs for this given PCIe device.
>                   -- cat-ing this file will return the number of VFs
>                      currently enabled on this PCIe device.
> sriov_disable_vfs -- echo-ing any number other than 0 disables all
>                       VFs associated with this PCIe device.
>
> VF enable and disablement is invoked much like other PCIe
> configuration functions -- via registered callbacks in the driver,
> i.e., probe, release, etc.
>
> v1->v2:
> This patch is based on previous 2 patches by Yinghai Lu
> that cleaned up the vga attributes for PCI devices under sysfs,
> and uses visibility-checking group attributes as recommended by
> Greg K-H.
>
> Signed-off-by: Donald Dutile <ddutile@redhat.com>

I'm not certain if having separate values/functions for enable and 
disabling VFs will work out very well.  It seems like it would probably 
make more sense just to have one value that manipulates NumVFs.  As is, 
in the sriov_enable_vfs case we would end up having to disable SR-IOV 
should we be changing the number of VFs anyway so it would probably make 
sense to just merge both values into a single one and use 0 as the value 
to disable SR-IOV.

Also in the naming scheme for the values it may preferable to use the 
names of the values from the SR-IOV PCIe capability to avoid any 
confusion on what the values represent.  I believe the names for the two 
values you are representing are TotalVFs and NumVFs.

Thanks,

Alex