[PATCH bpf-next] libbpf: Skip the pinning of global data map for old kernels.

[PATCH bpf-next] libbpf: Skip the pinning of global data map for old kernels.

[Shuyi Cheng]

Fix error: "failed to pin map: Bad file descriptor, path:
/sys/fs/bpf/_rodata_str1_1."

In the old kernel, the global data map will not be created, see [0]. So
we should skip the pinning of the global data map to avoid 
bpf_object__pin_maps returning error.

[0]: https://lore.kernel.org/bpf/20211123200105.387855-1-andrii@kernel.org

Signed-off-by: Shuyi Cheng <chengshuyi@linux.alibaba.com>
---
  tools/lib/bpf/libbpf.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6db0b5e8540e..d96cf49cebab 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7884,6 +7884,10 @@ int bpf_object__pin_maps(struct bpf_object *obj, 
const char *path)
  		char *pin_path = NULL;
  		char buf[PATH_MAX];

+		if (bpf_map__is_internal(map) &&
+		    !kernel_supports(obj, FEAT_GLOBAL_DATA))
+			continue;
+
  		if (path) {
  			int len;

-- 
2.19.1.6.gb485710b

Re: [PATCH bpf-next] libbpf: Skip the pinning of global data map for old kernels.

[Andrii Nakryiko]

On Thu, Dec 9, 2021 at 12:44 AM Shuyi Cheng
<chengshuyi@linux.alibaba.com> wrote:
>
>
> Fix error: "failed to pin map: Bad file descriptor, path:
> /sys/fs/bpf/_rodata_str1_1."
>
> In the old kernel, the global data map will not be created, see [0]. So
> we should skip the pinning of the global data map to avoid
> bpf_object__pin_maps returning error.
>
> [0]: https://lore.kernel.org/bpf/20211123200105.387855-1-andrii@kernel.org
>
> Signed-off-by: Shuyi Cheng <chengshuyi@linux.alibaba.com>
> ---
>   tools/lib/bpf/libbpf.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6db0b5e8540e..d96cf49cebab 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7884,6 +7884,10 @@ int bpf_object__pin_maps(struct bpf_object *obj,
> const char *path)
>                 char *pin_path = NULL;
>                 char buf[PATH_MAX];
>
> +               if (bpf_map__is_internal(map) &&
> +                   !kernel_supports(obj, FEAT_GLOBAL_DATA))


doing the same check in 3 different places sucks. Let's add "bool
skipped" to struct bpf_map, which will be set in one place (at the map
creation time) and then check during relocation and during pinning?

> +                       continue;
> +
>                 if (path) {
>                         int len;
>
> --
> 2.19.1.6.gb485710b

Re: [PATCH bpf-next] libbpf: Skip the pinning of global data map for old kernels.

[Shuyi Cheng]

On 12/10/21 1:26 AM, Andrii Nakryiko wrote:
> On Thu, Dec 9, 2021 at 12:44 AM Shuyi Cheng
> <chengshuyi@linux.alibaba.com> wrote:
>>
>>
>> Fix error: "failed to pin map: Bad file descriptor, path:
>> /sys/fs/bpf/_rodata_str1_1."
>>
>> In the old kernel, the global data map will not be created, see [0]. So
>> we should skip the pinning of the global data map to avoid
>> bpf_object__pin_maps returning error.
>>
>> [0]: https://lore.kernel.org/bpf/20211123200105.387855-1-andrii@kernel.org
>>
>> Signed-off-by: Shuyi Cheng <chengshuyi@linux.alibaba.com>
>> ---
>>    tools/lib/bpf/libbpf.c | 4 ++++
>>    1 file changed, 4 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 6db0b5e8540e..d96cf49cebab 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7884,6 +7884,10 @@ int bpf_object__pin_maps(struct bpf_object *obj,
>> const char *path)
>>                  char *pin_path = NULL;
>>                  char buf[PATH_MAX];
>>
>> +               if (bpf_map__is_internal(map) &&
>> +                   !kernel_supports(obj, FEAT_GLOBAL_DATA))
> 
> 
> doing the same check in 3 different places sucks. Let's add "bool
> skipped" to struct bpf_map, which will be set in one place (at the map
> creation time) and then check during relocation and during pinning?
>

Agree, thanks.

regards,
Shuyi



>> +                       continue;
>> +
>>                  if (path) {
>>                          int len;
>>
>> --
>> 2.19.1.6.gb485710b