Re: [PATCH bpf-next v8 1/8] selftests/bpf: Add ifdef guard for WRITE_ONCE macro in bpf_atomic.h

[Matt Bobrowski <mattbobrowski@google.com>]

On Tue, Apr 21, 2026 at 12:50:30PM -0400, Emil Tsalapatis wrote:
> The WRITE_ONCE macro is identically defined both in bpf_atomic.h
> and in bpf_arena_common.h. However, the bpf_atomic.h definition has no
> ifdef guard. If bpf_atomic.h is included after bpf_arena.common.h,
> compilation fails because of the duplicate definition.
> 
> Guard the definiton in bpf_atomic.h with and ifdef to let programs
> include the two headers in any order. Duplicating the definition is
> the simplest solution out of all the alternatives:
> 
> - Keeping one of the two existing definitions is not possible because
> both BPF atomics and arena programs need the macro, and the two features
> are independent. Using one should not require the header for the other.
> 
> - Factoring out the definition into a new header that only includes it
> is more churn than just duplicating it.
> 
> - Factoring out the definition into bpf_experimental.h requires all
> users of WRITE_ONCE to include the header. However, the arena library
> introduced in subsequent commits must be self-contained, while
> bpf_experimental.h is in the base selftests/bpf directory.
> 
> Both headers are moved to the arena library in a subsequent patch.
> 
> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>

Fair enough:

Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>