Re: [PATCH rdma-next v3 03/17] RDMA/core: Introduce generic buffer descriptor infrastructure for umem

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, May 06, 2026 at 04:14:34PM +0200, Jiri Pirko wrote:
> Wed, May 06, 2026 at 03:37:57PM +0200, jgg@ziepe.ca wrote:
> >On Mon, May 04, 2026 at 03:57:17PM +0200, Jiri Pirko wrote:
> >
> >> +/**
> >> + * ib_umem_get - Canonical on-demand umem getter.
> >> + * @device:        IB device.
> >> + * @udata:         uverbs udata bundle (may be NULL).
> >> + * @attr_id:       per-command UMEM attribute id; consulted if @udata is set.
> >> + * @legacy_filler: optional command-specific legacy attr filler.
> >> + *                 invoked if @udata is set.
> >> + * @va_fallback:   if true, build a VA-typed desc with @addr.
> >> + * @addr:          user VA, used if @va_fallback is true.
> >> + * @size:          driver-required minimum length.
> >> + * @access:        IB access flags forwarded to ib_umem_get_desc().
> >> + *
> >> + * Return: valid umem on success, ERR_PTR(...) on error, NULL
> >> + * if no source produced a buffer (only possible when @va_fallback is false).
> >> + */
> >> +struct ib_umem *ib_umem_get(struct ib_device *device, struct ib_udata *udata,
> >> +			    u16 attr_id,
> >> +			    ib_umem_buf_desc_filler_t legacy_filler,
> >> +			    bool va_fallback, u64 addr, size_t size, int access)
> >
> >I didn't try to look at what the drivers actually do, but I'm slightly
> >surprised not to see an addr_size here? Is it the case the drivers
> >don't have have a uhw->size to go along with their uhw->va?
> 
> "size_t size". What am I missing?

size is the minimum length, not the actual length passed into the
system call

> >> @@ -273,4 +273,27 @@ struct ib_uverbs_gid_entry {
> >>  	__u32 netdev_ifindex; /* It is 0 if there is no netdev associated with it */
> >>  };
> >>  
> >> +enum ib_uverbs_buffer_type {
> >> +	IB_UVERBS_BUFFER_TYPE_DMABUF,
> >> +	IB_UVERBS_BUFFER_TYPE_VA,
> >> +};
> >
> >I've learned it helps backporters to add the =0, =1
> 
> Why do we care about backporters? I mean, the mainline code is what we
> care of, and for that, enum default values are well defined and enough.
> What am I missing?

Well, just something I've thought about before. The rest of the uverbs
is pretty agressively not doing this so leave it

Jason