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Message-Id: <20210706095524.1883-1-vincent.donnefort@arm.com>
Date: Tue, 6 Jul 2021 09:55:24 +0000
From: Vincent Donnefort <vincent.donnefort@....com>
To: musl@...ts.openwall.com
Cc: jyknight@...gle.com,
Vincent Donnefort <vincent.donnefort@....com>
Subject: [PATCH v3] 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 that the system can contain, 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
otal 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 file /sys/devices/system/cpu/possible. This static file will not
change during the lifespan of the Linux kernel and contains a CPU mask
with all the CPUs that can be brought online.
diff --git a/src/conf/sysconf.c b/src/conf/sysconf.c
index 3baaed32..b4b842f5 100644
--- a/src/conf/sysconf.c
+++ b/src/conf/sysconf.c
@@ -1,8 +1,10 @@
+#include <ctype.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <sys/resource.h>
#include <signal.h>
+#include <stdbool.h>
#include <sys/sysinfo.h>
#include "syscall.h"
#include "libc.h"
@@ -22,6 +24,73 @@
#define RLIM(x) (-32768|(RLIMIT_ ## x))
+#define POSSIBLE_MAX_READ 128
+#define char_to_int(prev, num) (10 * prev + (num - '0'))
+
+static inline int get_nrprocessors_conf(void)
+{
+ FILE *f;
+ char buffer[POSSIBLE_MAX_READ];
+ int start_chunk = 0, end_chunk = -1;
+ unsigned int cnt = 0, i = 0;
+ size_t ret;
+
+ f = fopen("/sys/devices/system/cpu/possible", "r");
+ if (!f)
+ return 0;
+
+ ret = fread(buffer, sizeof(*buffer),
+ sizeof(buffer) / sizeof(*buffer), f);
+ if (!feof(f) || ferror(f) || ret < 2)
+ goto end;
+
+ /*
+ * Count the number of CPUs in the CPU mask. A CPU Mask is described by
+ * chunks. Chunks have the following format: "<start>-<end>" and are
+ * separated by ",". A chunk can be composed of a single CPU.
+ *
+ * e.g. "0-1,4" -> 3 CPUs
+ */
+ while (i < POSSIBLE_MAX_READ) {
+ if (buffer[i] == ',' || buffer[i] == '\0') {
+ if (end_chunk > -1)
+ cnt += (end_chunk - start_chunk) + 1;
+ else
+ cnt++;
+ start_chunk = 0;
+ end_chunk = -1;
+ if (buffer[i] == '\0')
+ break;
+ } else if (buffer[i] == '-') {
+ end_chunk = 0;
+ } else if (isdigit(buffer[i])) {
+ if (end_chunk == -1)
+ start_chunk =
+ char_to_int(start_chunk, buffer[i]);
+ else
+ end_chunk = char_to_int(end_chunk, buffer[i]);
+ }
+ i++;
+ }
+
+end:
+ fclose(f);
+
+ 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 +262,13 @@ 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
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