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From: Vincent Donnefort <vincent.donnefort@arm.com>
To: musl@lists.openwall.com
Cc: Vincent Donnefort <vincent.donnefort@arm.com>
Date: Wed,  5 May 2021 13:06:15 +0000
Message-Id: <20210505130615.6222-1-vincent.donnefort@arm.com>
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Subject: [musl] [PATCH] sysconf: add _SC_NPROCESSORS_CONF support

Currently, _SC_NPROCESSORS_CONF is always equal to _SC_NPROCESSORS_ONLN.
However, it is expected from the first one to give the total number of CPUs
in the system, while the later must return only the number of CPUs which
are currently online. This distinction is important for a software such as
trace-cmd. Trace-cmd is a front-end for the kernel tracing tool ftrace.
When recording traces, trace-cmd needs to get the total number of CPUs
available in the system (_SC_NPROCESSORS_CONF) and not only the online ones
otherwise if a CPU goes offline some data might be missing.

Hence, add a specific method to get _SC_NPROCESSORS_CONF, based on the
sysfs CPU entries /sys/devices/system/cpu/cpu[0-9]

diff --git a/src/conf/sysconf.c b/src/conf/sysconf.c
index 3baaed32..6281cfb6 100644
--- a/src/conf/sysconf.c
+++ b/src/conf/sysconf.c
@@ -1,12 +1,17 @@
+#include <ctype.h>
 #include <unistd.h>
 #include <limits.h>
 #include <errno.h>
 #include <sys/resource.h>
 #include <signal.h>
+#include <string.h>
 #include <sys/sysinfo.h>
 #include "syscall.h"
 #include "libc.h"
 
+#define _GNU_SOURCE
+#include <dirent.h>
+
 #define JT(x) (-256|(x))
 #define VER JT(1)
 #define JT_ARG_MAX JT(2)
@@ -22,6 +27,42 @@
 
 #define RLIM(x) (-32768|(RLIMIT_ ## x))
 
+static inline int get_nrprocessors_conf(void)
+{
+	DIR *d = opendir("/sys/devices/system/cpu");
+	struct dirent *de;
+	unsigned int cnt = 0;
+
+	if (!d)
+		return -1;
+
+	while ((de = readdir(d))) {
+		if (de->d_type == DT_DIR &&
+		    strlen(de->d_name) > 3 &&
+		    de->d_name[0] == 'c' &&
+		    de->d_name[1] == 'p' &&
+		    de->d_name[2] == 'u' &&
+		    isdigit(de->d_name[3]))
+			cnt++;
+	}
+
+	closedir(d);
+
+	return cnt;
+}
+
+static inline int get_nrprocessors_onln(void)
+{
+	unsigned char set[128] = {1};
+	int i, cnt;
+
+	__syscall(SYS_sched_getaffinity, 0, sizeof set, set);
+	for (i=cnt=0; i<sizeof set; i++)
+		for (; set[i]; set[i]&=set[i]-1, cnt++);
+
+	return cnt;
+}
+
 long sysconf(int name)
 {
 	static const short values[] = {
@@ -193,14 +234,13 @@ long sysconf(int name)
 		return SEM_VALUE_MAX;
 	case JT_DELAYTIMER_MAX & 255:
 		return DELAYTIMER_MAX;
-	case JT_NPROCESSORS_CONF & 255:
+	case JT_NPROCESSORS_CONF & 255: ;
+		int cnt = get_nrprocessors_conf();
+		if (cnt > 0)
+			return cnt;
+		return get_nrprocessors_onln();
 	case JT_NPROCESSORS_ONLN & 255: ;
-		unsigned char set[128] = {1};
-		int i, cnt;
-		__syscall(SYS_sched_getaffinity, 0, sizeof set, set);
-		for (i=cnt=0; i<sizeof set; i++)
-			for (; set[i]; set[i]&=set[i]-1, cnt++);
-		return cnt;
+		return get_nrprocessors_onln();
 	case JT_PHYS_PAGES & 255:
 	case JT_AVPHYS_PAGES & 255: ;
 		unsigned long long mem;
-- 
2.27.0