Re: [PATCH rdma-next v2 01/15] RDMA/core: Introduce generic buffer descriptor infrastructure for umem

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Apr 23, 2026 at 03:08:19PM +0200, Jiri Pirko wrote:
> >Whereas if the driver has to define mandatory attributes to pass its
> >unique ib_uverbs_buffer_desc I'm not worried about future ABI because
> >eveything is now clearly labled and the uattrs system already has a
> >built in way to reject using a future kernel's driver attribute on an
> >older kernel.
> 
> Hmm, but the attr may be optional, yet silently ignored (for example by
> driver that does not support it). I think we still need to sanitize such
> silent ignores.

The kernel schema describes attributes as mandatory and optional. If a
mandatory attribute is missing then the ioctl will fail before
reaching the handler.

The userspace can also describe the attribute it is passing in as
mandatory and optional via UVERBS_ATTR_F_MANDATORY. If this flag is
set and the kernel does not have the attribute in its schema then the
ioctl will fail before invoking the handler.

The only remaining case is where the driver has an attribute in its
schema and doesn't actually use it for some reason. I'm not sure this
is so important to worry about, at least from an ABI perspective
everything is properly labeled and there won't be forward/backwards
compat issues.

Jason