Subject: Re: [PATCH] selftests/bpf: Fix bpf selftest build error

From: Venkat Rao Bagalkote <[email-masked]>
Date: Mon, 12 May 2025 09:24:10 +0530

On 09/05/25 5:53 pm, Saket Kumar Bhaskar wrote:
> On linux-next, build for bpf selftest displays an error due to
> mismatch in the expected function signature of bpf_testmod_test_read
> and bpf_testmod_test_write.
>
> Commit 97d06802d10a ("sysfs: constify bin_attribute argument of bin_attribute::read/write()")
> changed the required type for struct bin_attribute to const struct bin_attribute.
>
> To resolve the error, update corresponding signature for the callback.
>
> Reported-by: Venkat Rao Bagalkote <[email-masked]>
> Closes: https://lore.kernel.org/all/[email-masked]/
> Signed-off-by: Saket Kumar Bhaskar <[email-masked]>
> ---
>   tools/testing/selftests/bpf/test_kmods/bpf_testmod.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> index 2e54b95ad898..194c442580ee 100644
> --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> @@ -385,7 +385,7 @@ int bpf_testmod_fentry_ok;
>   
>   noinline ssize_t
>   bpf_testmod_test_read(struct file *file, struct kobject *kobj,
> -		      struct bin_attribute *bin_attr,
> +		      const struct bin_attribute *bin_attr,
>   		      char *buf, loff_t off, size_t len)
>   {
>   	struct bpf_testmod_test_read_ctx ctx = {
> @@ -465,7 +465,7 @@ ALLOW_ERROR_INJECTION(bpf_testmod_test_read, ERRNO);
>   
>   noinline ssize_t
>   bpf_testmod_test_write(struct file *file, struct kobject *kobj,
> -		      struct bin_attribute *bin_attr,
> +		      const struct bin_attribute *bin_attr,
>   		      char *buf, loff_t off, size_t len)
>   {
>   	struct bpf_testmod_test_write_ctx ctx = {

Tested this patch by applying on top of next-20250508 and if fixes the 
build issue. Hence,

Tested-by: Venkat Rao Bagalkote <[email-masked]>

commit f48887a98b78880b7711aca311fbbbcaad6c4e3b (tag: next-20250508, 
origin/master, origin/HEAD, bpf_arena)
Author: Stephen Rothwell <[email-masked]>
Date:   Thu May 8 18:45:50 2025 +1000

     Add linux-next specific files for 20250508

After this patch:

   TEST-OBJ [test_progs-cpuv4] xdp_flowtable.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_info.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_link.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_metadata.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_noinline.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_perf.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_synproxy.test.o
   TEST-OBJ [test_progs-cpuv4] xdp_vlan.test.o
   TEST-OBJ [test_progs-cpuv4] xdpwall.test.o
   TEST-OBJ [test_progs-cpuv4] xfrm_info.test.o
   BINARY   bench
   BINARY   test_maps
   BINARY   test_progs
   BINARY   test_progs-no_alu32
   BINARY   test_progs-cpuv4

Before this patch:

   CLANG 
/root/linux-next/tools/testing/selftests/bpf/tools/build/bpftool/profiler.bpf.o
bpf_testmod.c:494:17: error: initialization of ‘ssize_t (*)(struct file 
*, struct kobject *, const struct bin_attribute *, char *, loff_t,  
size_t)’ {aka ‘long int (*)(struct file *, struct kobject *, const 
struct bin_attribute *, char *, long long int,  long unsigned int)’} 
from incompatible pointer type ‘ssize_t (*)(struct file *, struct 
kobject *, struct bin_attribute *, char *, loff_t, size_t)’ {aka ‘long 
int (*)(struct file *, struct kobject *, struct bin_attribute *, char *, 
long long int,  long unsigned int)’} [-Wincompatible-pointer-types]
   494 |         .read = bpf_testmod_test_read,
       |                 ^~~~~~~~~~~~~~~~~~~~~
bpf_testmod.c:494:17: note: (near initialization for 
‘bin_attr_bpf_testmod_file.read’)
bpf_testmod.c:495:18: error: initialization of ‘ssize_t (*)(struct file 
*, struct kobject *, const struct bin_attribute *, char *, loff_t,  
size_t)’ {aka ‘long int (*)(struct file *, struct kobject *, const 
struct bin_attribute *, char *, long long int,  long unsigned int)’} 
from incompatible pointer type ‘ssize_t (*)(struct file *, struct 
kobject *, struct bin_attribute *, char *, loff_t, size_t)’ {aka ‘long 
int (*)(struct file *, struct kobject *, struct bin_attribute *, char *, 
long long int,  long unsigned int)’} [-Wincompatible-pointer-types]
   495 |         .write = bpf_testmod_test_write,
       |                  ^~~~~~~~~~~~~~~~~~~~~~
bpf_testmod.c:495:18: note: (near initialization for 
‘bin_attr_bpf_testmod_file.write’)
make[4]: *** [/root/linux-next/scripts/Makefile.build:203: 
bpf_testmod.o] Error 1
make[3]: *** [/root/linux-next/Makefile:2009: .] Error 2
make[2]: *** [Makefile:248: __sub-make] Error 2
make[1]: *** [Makefile:18: all] Error 2
make: *** [Makefile:282: test_kmods/bpf_testmod.ko] Error 2

Regards,

Venkat.