[PATCH v5 3/6] iommu: Add return value rules to attach_dev op and APIs

[Jason Gunthorpe]

On Thu, Sep 22, 2022 at 01:54:08AM -0700, Nicolin Chen wrote:
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
> 
> This is a soft failure that can be resolved by using a different domain.
> 
> Provide a dedicated errno EINVAL from the IOMMU driver during attach that
> the reason why the attach failed is because of domain incompatibility.
> 
> VFIO can use this to know that the attach is a soft failure and it should
> continue searching. Otherwise, the attach will be a hard failure and VFIO
> will return the code to userspace.
> 
> Update kdocs to add rules of return value to the attach_dev op and APIs.
> 
> Suggested-by: Jason Gunthorpe <jgg at nvidia.com>
> Reviewed-by: Kevin Tian <kevin.tian at intel.com>
> Signed-off-by: Nicolin Chen <nicolinc at nvidia.com>
> ---
>  drivers/iommu/iommu.c | 24 ++++++++++++++++++++++++
>  include/linux/iommu.h | 12 ++++++++++++
>  2 files changed, 36 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg at nvidia.com>

Jason