libbpf: Use page size as max_entries when probing ring buffer map

[ Upstream commit 689eb2f1ba46b4b02195ac2a71c55b96d619ebf8 ]

Using page size as max_entries 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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221116072351.1168938-2-houtao@huaweicloud.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index cd8c703..8f42547 100644 (file)
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -245,7 +245,7 @@ bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
        case BPF_MAP_TYPE_RINGBUF:
                key_size = 0;
                value_size = 0;
-               max_entries = 4096;
+               max_entries = sysconf(_SC_PAGE_SIZE);
                break;
        case BPF_MAP_TYPE_UNSPEC:
        case BPF_MAP_TYPE_HASH: