Re: [PATCH 2/2] test/cbpf_filter: skip when openat2.h is not available

[Jens Axboe <axboe@kernel.dk>]

On 3/14/26 11:02 PM, Yang Xiuwei wrote:
> Hi Jens,
> 
> On 2026-03-14 13:35 UTC, Jens Axboe wrote:
>> liburing defines open_how if it's not in the system headers. I feel
>> like all you need to do here is remove the openat2.h include, rather
>> than disable the test entirely?
> 
> Thanks for the suggestion. I had actually tried that first: removing only the
> #include <linux/openat2.h> and relying on liburing's compat for struct open_how.
> It turned out that this test also uses the RESOLVE_IN_ROOT macro (and the
> filter logic is built around it). Without the header, the build fails with
> 'RESOLVE_IN_ROOT' undeclared. RESOLVE_IN_ROOT and the other RESOLVE_* flags
> come from <linux/openat2.h>; compat.h only provides struct open_how when the
> header is missing, not those constants.
> 
> Defining RESOLVE_IN_ROOT (and friends) ourselves in compat or in the test
> would duplicate kernel UAPI and could get out of sync if the kernel ever
> changes them. So I went back to the more conservative approach: wrap the
> test in #ifdef CONFIG_HAVE_OPEN_HOW and provide a stub main that returns
> T_EXIT_SKIP when openat2.h is not available. The test then always compiles;
> on systems without the header it simply skips at runtime.
> 
> If you have a better approach in mind, I'd be glad to follow that instead.

I think just defining RESOLVE_IN_ROOT if it's not available should be
fine. And yes the test will always compile when you stub everything out,
but it also won't do anything at all. This will prevent running this
test case on a host with old headers, but with a current kernel. How
about the below, hopefully that should do it. That'll keep the test
functional, rather than wrap it all in a define that just disables it
entirely.

diff --git a/test/cbpf_filter.c b/test/cbpf_filter.c
index 41fd284e4434..b80b15033662 100644
--- a/test/cbpf_filter.c
+++ b/test/cbpf_filter.c
@@ -15,12 +15,15 @@
 #include <sys/wait.h>
 #include <sys/prctl.h>
 #include <linux/filter.h>
-#include <linux/openat2.h>
 
 #include "liburing.h"
 #include "liburing/io_uring/bpf_filter.h"
 #include "helpers.h"
 
+#ifndef RESOLVE_IN_ROOT
+#define RESOLVE_IN_ROOT	0x10
+#endif
+
 /*
  * cBPF filter context layout (struct io_uring_bpf_ctx):
  *   offset 0:  user_data (u64)

-- 
Jens Axboe