Re: [PATCH] iommufd: fix returns ENOENT in iommufd_viommu_get_vdev_id()

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Aug 04, 2025 at 11:25:42AM +0000, Pranjal Shrivastava wrote:
> On Mon, Aug 04, 2025 at 06:08:59PM +0800, Richard Gemego wrote:
> > In iommufd_viommu_get_vdev_id(), if viommu does not have any vdevs, fix
> > this func to return 0 instead of ENOENT.

I think this is missing some justification explaining why this is
a fix.

> > Fixes: ea94b211c548 ("iommufd/viommu: Add iommufd_viommu_get_vdev_id helper")
> > Signed-off-by: Richard Gemego <richardgemego@gmail.com>
> > Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
> > ---
> >  drivers/iommu/iommufd/driver.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
> > index 922cd1fe7ec2..ad635af8555b 100644
> > --- a/drivers/iommu/iommufd/driver.c
> > +++ b/drivers/iommu/iommufd/driver.c
> > @@ -68,6 +68,7 @@ int iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
> >  			break;
> >  		}
> >  	}
> > +	if (!index) 
> > +		rc = 0;
> >  	xa_unlock(&viommu->vdevs);
> >  	return rc;
> >  }
> 
> I'm afraid, I don't understand the motivation behind this? IIUC, if a 
> dev is not associated to the vIOMMU -ENOENT is returned. This patch
> seems to be returning 0 when the xarray is empty. The issue is that
> returning 0, would indicate the caller that `*vdev_id` holds a valid 
> value which doesn't seem to be the case here?

The function is designed to return -ENOENT for an empty xarray:

/* Return -ENOENT if device is not associated to the vIOMMU */

And 0 would be a valid vdev ID in the xarray.

Nicolin