Re: [PATCH bpf-next] bpf: Replace __opt annotation with __nullable for kfuncs

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-12-31 at 15:26 -0800, Puranjay Mohan wrote:
> The __opt annotation was originally introduced specifically for
> buffer/size argument pairs in bpf_dynptr_slice() and
> bpf_dynptr_slice_rdwr(), allowing the buffer pointer to be NULL while
> still validating the size as a constant.  The __nullable annotation
> serves the same purpose but is more general and is already used
> throughout the BPF subsystem for raw tracepoints, struct_ops, and other
> kfuncs.
> 
> This patch unifies the two annotations by replacing __opt with
> __nullable.  The key change is in the verifier's
> get_kfunc_ptr_arg_type() function, where mem/size pair detection is now
> performed before the nullable check.  This ensures that buffer/size
> pairs are correctly classified as KF_ARG_PTR_TO_MEM_SIZE even when the
> buffer is nullable, while adding an !arg_mem_size condition to the
> nullable check prevents interference with mem/size pair handling.
> 
> When processing KF_ARG_PTR_TO_MEM_SIZE arguments, the verifier now uses
> is_kfunc_arg_nullable() instead of the removed is_kfunc_arg_optional()
> to determine whether to skip size validation for NULL buffers.
> 
> This is the first documentation added for the __nullable annotation,
> which has been in use since it was introduced but was previously
> undocumented.
> 
> No functional changes to verifier behavior - nullable buffer/size pairs
> continue to work exactly as before.
> 
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
> ---

Lgtm, thank you for the quick turnaround.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]