Subject: Re: [PATCH V6 mlx5-next 07/15] vfio: Have the core code decode the VFIO_DEVICE_FEATURE ioctl

From: Jason Gunthorpe <[email-masked]>
Date: Tue, 1 Feb 2022 11:49:29 -0400

On Tue, Feb 01, 2022 at 08:47:58AM -0700, Alex Williamson wrote:
> On Mon, 31 Jan 2022 20:11:48 -0400
> Jason Gunthorpe <[email-masked]> wrote:
> 
> > On Mon, Jan 31, 2022 at 04:41:43PM -0700, Alex Williamson wrote:
> > > > +int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
> > > > +				void __user *arg, size_t argsz)
> > > > +{
> > > > +	struct vfio_pci_core_device *vdev =
> > > > +		container_of(device, struct vfio_pci_core_device, vdev);
> > > > +	uuid_t uuid;
> > > > +	int ret;  
> > > 
> > > Nit, should uuid at least be scoped within the token code?  Or token
> > > code pushed to a separate function?  
> > 
> > Sure, it wasn't done before, but it would be nicer,.
> > 
> > > > +static inline int vfio_check_feature(u32 flags, size_t argsz, u32 supported_ops,
> > > > +				    size_t minsz)
> > > > +{
> > > > +	if ((flags & (VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_SET)) &
> > > > +	    ~supported_ops)
> > > > +		return -EINVAL;  
> > > 
> > > These look like cases where it would be useful for userspace debugging
> > > to differentiate errnos.  
> > 
> > I tried to keep it unchanged from what it was today.
> > 
> > > -EOPNOTSUPP?  
> > 
> > This would be my preference, but it would also be the first use in
> > vfio
> > 
> > > > +	if (flags & VFIO_DEVICE_FEATURE_PROBE)
> > > > +		return 0;
> > > > +	/* Without PROBE one of GET or SET must be requested */
> > > > +	if (!(flags & (VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_SET)))
> > > > +		return -EINVAL;
> > > > +	if (argsz < minsz)
> > > > +		return -EINVAL;  
> > >
> > > -ENOSPC?  
> > 
> > Do you want to do all of these minsz then? There are lots..
> 
> Hmm, maybe this one is more correct as EINVAL.  In the existing use
> cases the structure associated with the feature is a fixed size, so
> it's not a matter that we down have space for a return like
> HOT_RESET_INFO, it's simply invalid arguments by the caller.  I guess
> keep this one as EINVAL, but EOPNOTSUPP seems useful for the
> previous.

Do you want EOPNOTSUPP or ENOTTY like most other places in vfio?

Jason