Re: [PATCH bpf 1/4] libbpf: Adjust ring buffer size when probing ring buffer map

[sdf@google.com]

On 11/11, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>

> Adjusting the size of ring buffer when probing ring buffer map, else
> the probe may fail on host with 64KB page size (e.g., an ARM64 host).

> After the fix, the output of "bpftool feature" on above host will be
> correct.

> Before :
>      eBPF map_type ringbuf is NOT available
>      eBPF map_type user_ringbuf is NOT available

> After :
>      eBPF map_type ringbuf is available
>      eBPF map_type user_ringbuf is available

> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
>   tools/lib/bpf/libbpf.c          | 2 +-
>   tools/lib/bpf/libbpf_internal.h | 2 ++
>   tools/lib/bpf/libbpf_probes.c   | 2 +-
>   3 files changed, 4 insertions(+), 2 deletions(-)

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 184ce1684dcd..907f735568ae 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2353,7 +2353,7 @@ int parse_btf_map_def(const char *map_name, struct  
> btf *btf,
>   	return 0;
>   }

> -static size_t adjust_ringbuf_sz(size_t sz)
> +size_t adjust_ringbuf_sz(size_t sz)
>   {
>   	__u32 page_sz = sysconf(_SC_PAGE_SIZE);
>   	__u32 mul;
> diff --git a/tools/lib/bpf/libbpf_internal.h  
> b/tools/lib/bpf/libbpf_internal.h
> index 377642ff51fc..99dc4d6a19be 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -576,4 +576,6 @@ static inline bool is_pow_of_2(size_t x)
>   #define PROG_LOAD_ATTEMPTS 5
>   int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int  
> attempts);

> +size_t adjust_ringbuf_sz(size_t sz);
> +
>   #endif /* __LIBBPF_LIBBPF_INTERNAL_H */
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index f3a8e8e74eb8..29a1db2645fd 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -234,7 +234,7 @@ static int probe_map_create(enum bpf_map_type  
> map_type)
>   	case BPF_MAP_TYPE_USER_RINGBUF:
>   		key_size = 0;
>   		value_size = 0;
> -		max_entries = 4096;
> +		max_entries = adjust_ringbuf_sz(4096);

Why not pass PAGE_SIZE directly here? Something like:

max_entries = sysconf(_SC_PAGE_SIZE);

?

>   		break;
>   	case BPF_MAP_TYPE_STRUCT_OPS:
>   		/* we'll get -ENOTSUPP for invalid BTF type ID for struct_ops */
> --
> 2.29.2