linux-kernel - [PATCH AUTOSEL 5.10 04/10] libbpf: Use page size as max

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Date:   Tue,  6 Dec 2022 04:50:21 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Hou Tao <houtao1@...wei.com>, Andrii Nakryiko <andrii@...nel.org>,
        Sasha Levin <sashal@...nel.org>, ast@...nel.org,
        daniel@...earbox.net, bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 04/10] libbpf: Use page size as max_entries when probing ring buffer map

From: Hou Tao <houtao1@...wei.com>

[ 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@...wei.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/bpf/20221116072351.1168938-2-houtao@huaweicloud.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/lib/bpf/libbpf_probes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index d38284a3aaf0..13393f0eab25 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -244,7 +244,7 @@ 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:
-- 
2.35.1