X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=libringbuffer%2Fsmp.c;h=966556dcee15cf38b0a4b6e86d1f47ccd878169b;hb=bb6e798cb47c1a16dbeaae168903ae9760838815;hp=9e7114be8a40f3349b8a8942131f440ce0514311;hpb=3fbec7dc3645facd9e809cf161ba3435a377ce56;p=lttng-ust.git

diff --git a/libringbuffer/smp.c b/libringbuffer/smp.c
index 9e7114be..966556dc 100644
--- a/libringbuffer/smp.c
+++ b/libringbuffer/smp.c
@@ -2,6 +2,7 @@
  * libringbuffer/smp.c
  *
  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -20,16 +21,24 @@
 
 #define _GNU_SOURCE
 #define _LGPL_SOURCE
-#include <unistd.h>
+#include <assert.h>
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
 #include <pthread.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "align.h"
 #include "smp.h"
+#include "usterr-signal-safe.h"
 
 int __num_possible_cpus;
 
-void _get_num_possible_cpus(void)
+#if (defined(__GLIBC__) || defined( __UCLIBC__))
+int get_num_possible_cpus_fallback(void)
 {
-	int result;
-
 	/* On Linux, when some processors are offline
 	 * _SC_NPROCESSORS_CONF counts the offline
 	 * processors, whereas _SC_NPROCESSORS_ONLN
@@ -38,8 +47,186 @@ void _get_num_possible_cpus(void)
 	 * this sysconf, in which case the arrays
 	 * indexed by processor would overflow.
 	 */
-	result = sysconf(_SC_NPROCESSORS_CONF);
-	if (result == -1)
+	return sysconf(_SC_NPROCESSORS_CONF);
+}
+
+#else
+
+/*
+ * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
+ * return the number of configured CPUs in the system but relies on the cpu
+ * affinity mask of the current task.
+ *
+ * So instead we use a strategy similar to GLIBC's, counting the cpu
+ * directories in "/sys/devices/system/cpu" and fallback on the value from
+ * sysconf if it fails.
+ */
+
+#include <dirent.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#define __max(a,b) ((a)>(b)?(a):(b))
+
+int get_num_possible_cpus_fallback(void)
+{
+	int count = 0;
+	DIR *cpudir;
+	struct dirent *entry;
+
+	cpudir = opendir("/sys/devices/system/cpu");
+	if (cpudir == NULL)
+		goto end;
+
+	/*
+	 * Count the number of directories named "cpu" followed by and
+	 * integer. This is the same strategy as glibc uses.
+	 */
+	while ((entry = readdir(cpudir))) {
+		if (entry->d_type == DT_DIR &&
+			strncmp(entry->d_name, "cpu", 3) == 0) {
+
+			char *endptr;
+			unsigned long cpu_num;
+
+			cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
+			if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
+					&& (*endptr == '\0')) {
+				count++;
+			}
+		}
+	}
+
+end:
+	/*
+	 * Get the sysconf value as a fallback. Keep the highest number.
+	 */
+	return __max(sysconf(_SC_NPROCESSORS_CONF), count);
+}
+#endif
+
+/*
+ * Get the CPU possible mask string from sysfs.
+ *
+ * buf: the buffer where the mask will be read.
+ * max_bytes: the maximum number of bytes to write in the buffer.
+ *
+ * Returns the number of bytes read or -1 on error.
+ */
+int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)
+{
+	ssize_t bytes_read = 0;
+	size_t total_bytes_read = 0;
+	int fd = -1, ret = -1;
+
+	if (buf == NULL)
+		goto end;
+
+	fd = open("/sys/devices/system/cpu/possible", O_RDONLY);
+	if (fd < 0)
+		goto end;
+
+	do {
+		bytes_read = read(fd, buf + total_bytes_read,
+				max_bytes - total_bytes_read);
+
+		if (bytes_read < 0) {
+			if (errno == EINTR) {
+				continue;	/* retry operation */
+			} else {
+				goto end;
+			}
+		}
+
+		total_bytes_read += bytes_read;
+		assert(total_bytes_read <= max_bytes);
+	} while (max_bytes > total_bytes_read && bytes_read > 0);
+
+	/*
+	 * Make sure the mask read is a null terminated string.
+	 */
+	if (total_bytes_read < max_bytes)
+		buf[total_bytes_read] = '\0';
+	else
+		buf[max_bytes - 1] = '\0';
+
+	if (total_bytes_read > INT_MAX)
+		goto end;
+
+	ret = (int) total_bytes_read;
+
+end:
+	if (fd >= 0 && close(fd) < 0)
+		PERROR("close");
+
+	return ret;
+}
+
+/*
+ * Get the number of CPUs from the possible cpu mask.
+ *
+ * pmask: the mask to parse.
+ * len: the len of the mask excluding '\0'.
+ *
+ * Returns the number of possible CPUs from the mask or 0 on error.
+ */
+int get_num_possible_cpus_from_mask(const char *pmask, size_t len)
+{
+	ssize_t i;
+	unsigned long cpu_index;
+	char *endptr;
+
+	/* We need at least one char to read */
+	if (len < 1)
+		goto error;
+
+	/* Start from the end to read the last CPU index. */
+	for (i = len - 1; i > 0; i--) {
+		/* Break when we hit the first separator. */
+		if ((pmask[i] == ',') || (pmask[i] == '-')) {
+			i++;
+			break;
+		}
+	}
+
+	cpu_index = strtoul(&pmask[i], &endptr, 10);
+
+	/*
+	 * If we read a CPU index, increment it by one to return a number of
+	 * CPUs.
+	 */
+	if ((&pmask[i] != endptr) && (cpu_index < INT_MAX))
+		return (int) cpu_index + 1;
+
+error:
+	return 0;
+}
+
+void _get_num_possible_cpus(void)
+{
+	int ret;
+	char buf[LTTNG_UST_CPUMASK_SIZE];
+
+	/* Get the possible cpu mask from sysfs, fallback to sysconf. */
+	ret = get_possible_cpu_mask_from_sysfs((char *) &buf, LTTNG_UST_CPUMASK_SIZE);
+	if (ret <= 0)
+		goto fallback;
+
+	/* Parse the possible cpu mask, on failure fallback to sysconf. */
+	ret = get_num_possible_cpus_from_mask((char *) &buf, ret);
+	if (ret > 0)
+		goto end;
+
+fallback:
+	/* Fallback to sysconf. */
+	ret = get_num_possible_cpus_fallback();
+
+end:
+	/* If all methods failed, don't store the value. */
+	if (ret < 1)
 		return;
-	__num_possible_cpus = result;
+
+	__num_possible_cpus = ret;
 }