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* [musl] [PATCH] sysconf: add _SC_NPROCESSORS_CONF support
@ 2021-05-05 13:06 Vincent Donnefort
  2021-05-05 14:04 ` Alexander Monakov
  0 siblings, 1 reply; 4+ messages in thread
From: Vincent Donnefort @ 2021-05-05 13:06 UTC (permalink / raw)
  To: musl; +Cc: Vincent Donnefort

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


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-05-05 17:21 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-05 13:06 [musl] [PATCH] sysconf: add _SC_NPROCESSORS_CONF support Vincent Donnefort
2021-05-05 14:04 ` Alexander Monakov
2021-05-05 17:05   ` Vincent Donnefort
2021-05-05 17:20   ` James Y Knight

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