linux-kernel - [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible

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Date:   Tue, 21 Sep 2021 11:34:34 +0530
From:   Muhammad Falak R Wani <falakreyaz@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Muhammad Falak R Wani <falakreyaz@...il.com>
Subject: [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus

Simplify libbpf_num_possible_cpus by using sysconf(_SC_NPROCESSORS_CONF)
instead of parsing a file.
This patch is a part of libbpf-1.0 milestone.

Reference: https://github.com/libbpf/libbpf/issue/383

Signed-off-by: Muhammad Falak R Wani <falakreyaz@...il.com>
---
 tools/lib/bpf/libbpf.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index da65a1666a5e..1d730b08ee44 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10765,25 +10765,15 @@ int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz)
 
 int libbpf_num_possible_cpus(void)
 {
-	static const char *fcpu = "/sys/devices/system/cpu/possible";
 	static int cpus;
-	int err, n, i, tmp_cpus;
-	bool *mask;
+	int tmp_cpus;
 
 	tmp_cpus = READ_ONCE(cpus);
 	if (tmp_cpus > 0)
 		return tmp_cpus;
 
-	err = parse_cpu_mask_file(fcpu, &mask, &n);
-	if (err)
-		return libbpf_err(err);
-
-	tmp_cpus = 0;
-	for (i = 0; i < n; i++) {
-		if (mask[i])
-			tmp_cpus++;
-	}
-	free(mask);
+	tmp_cpus = sysconf(_SC_NPROCESSORS_CONF);
+	/* sysconf sets errno; no need to use libbpf_err */
 
 	WRITE_ONCE(cpus, tmp_cpus);
 	return tmp_cpus;
-- 
2.17.1