Re: [PATCH rdma-next] RDMA/mana_ib: Retain create CQ flags field name

[Leon Romanovsky <leon@kernel.org>]

On Mon, Aug 03, 2026 at 01:59:07PM +0200, Jiri Pirko wrote:
> Fri, Jul 31, 2026 at 02:54:31PM +0200, kotaranov@microsoft.com wrote:
> >> From: Jiri Pirko <jiri@nvidia.com>
> >> 
> >> Commit eb70d83a8645 ("RDMA/mana_ib: Adopt robust udata") renamed the
> >> "flags" field of struct mana_ib_create_cq to "comp_mask", as
> >> ib_copy_validate_udata_in_cm() only validates a member with that name.
> >> 
> >> The layout did not change, but the field has been a part of the UAPI since
> >> commit 44b607ad4cdf ("RDMA/mana_ib: implement uapi for creation of rnic
> >> cq"), so the rename breaks userspace referring to it, for example the mana
> >> provider of rdma-core assigning cmd_drv->flags.
> >> 
> >> Convert the field to a union providing both names, so that
> >> ib_copy_validate_udata_in_cm() still finds "comp_mask" and userspace keeps
> >> "flags", without having to add a helper for this single case.
> >> 
> >
> >Thanks for the patch, but my understanding that it is a common practice to rename the fields,
> >and kernels headers should not accumulate historical names. 
> 
> That is not doable in UAPI.

There are multiple levels of UAPI contracts. In RDMA, we guarantee
binary compatibility because userspace (rdma-core) is effectively the
second half of the RDMA driver stack. These drivers do not exist
without rdma-core.

As such, this is exactly how the RDMA UAPI is intended to work.


> Some userspace app, like rdma-core in this case, might use it and rename breaks the compilation. Some other
> app you don't know about may use it.

rdma-core does not use these headers directly. Instead, it vendors
them in the kernel-headers directories specifically for this purpose.

> 
> 
> >I also faced a similar problem from renames in other providers, when I needed a new kernel header in rdma-core.
> >If this breaks your rdma-core in a PR, just remove the field rename in kernel update commit as that header update commit is not getting merged anyway from your PR.
> >My understanding that maintainers of RDMA-core will merge the kernel header update, and will bring this change from my PR:
> >https://github.com/linux-rdma/rdma-core/pull/1765/commits/0dcadd9316f1b98e21973e3a6e0f96186d49bd5a
> 
> this is not how UAPI can be changed :/ It simply can't be changed.

It can, at least in RDMA and elsewhere in the kernel, where user
access is provided through properly designed libraries.

Thanks

> 
> 
> >
> >- Konstantin
> >
> >> Fixes: eb70d83a8645 ("RDMA/mana_ib: Adopt robust udata")
> >> Signed-off-by: Jiri Pirko <jiri@nvidia.com>
> >> ---
> >>  include/uapi/rdma/mana-abi.h | 5 ++++-
> >>  1 file changed, 4 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/include/uapi/rdma/mana-abi.h b/include/uapi/rdma/mana-abi.h
> >> index 410f0ddc8c89..431c7076f20a 100644
> >> --- a/include/uapi/rdma/mana-abi.h
> >> +++ b/include/uapi/rdma/mana-abi.h
> >> @@ -25,7 +25,10 @@ enum mana_ib_create_cq_flags {
> >> 
> >>  struct mana_ib_create_cq {
> >>  	__aligned_u64 buf_addr;
> >> -	__u16	comp_mask;
> >> +	union {
> >> +		__u16	comp_mask;
> >> +		__u16	flags; /* the original name of the field */
> >> +	};
> >>  	__u16	reserved0;
> >>  	__u32	reserved1;
> >>  };
> >> --
> >> 2.54.0
> >