* 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
*/
#define _GNU_SOURCE
-#include <unistd.h>
-#include "usterr.h"
+#define _LGPL_SOURCE
+#include <assert.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
#include <pthread.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+
#include "smp.h"
+#include "usterr-signal-safe.h"
+
+#define __max(a,b) ((a)>(b)?(a):(b))
int __num_possible_cpus;
-void _get_num_possible_cpus(void)
+/*
+ * As a fallback to parsing the CPU mask in "/sys/devices/system/cpu/possible",
+ * iterate on all the folders in "/sys/devices/system/cpu" that start with
+ * "cpu" followed by an integer, keep the highest CPU id encountered during
+ * this iteration and add 1 to get a number of CPUs.
+ *
+ * Then get the value from sysconf(_SC_NPROCESSORS_CONF) as a fallback and
+ * return the highest one.
+ *
+ * On Linux, using the value from sysconf can be unreliable since the way it
+ * counts CPUs varies between C libraries and even between versions of the same
+ * library. If we used it directly, getcpu() could return a value greater than
+ * this sysconf, in which case the arrays indexed by processor would overflow.
+ *
+ * As another example, 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.
+ *
+ * Returns 0 or less on error.
+ */
+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
- * does not. If we used _SC_NPROCESSORS_ONLN,
- * getcpu() could return a value greater than
- * this sysconf, in which case the arrays
- * indexed by processor would overflow.
+ long max_cpuid = -1;
+
+ DIR *cpudir;
+ struct dirent *entry;
+
+ cpudir = opendir("/sys/devices/system/cpu");
+ if (cpudir == NULL)
+ goto end;
+
+ /*
+ * Iterate on all directories named "cpu" followed by an integer.
*/
- result = sysconf(_SC_NPROCESSORS_CONF);
- if (result == -1)
+ while ((entry = readdir(cpudir))) {
+ if (entry->d_type == DT_DIR &&
+ strncmp(entry->d_name, "cpu", 3) == 0) {
+
+ char *endptr;
+ long cpu_id;
+
+ cpu_id = strtol(entry->d_name + 3, &endptr, 10);
+ if ((cpu_id < LONG_MAX) && (endptr != entry->d_name + 3)
+ && (*endptr == '\0')) {
+ if (cpu_id > max_cpuid)
+ max_cpuid = cpu_id;
+ }
+ }
+ }
+
+ if (closedir(cpudir))
+ PERROR("closedir");
+
+ /*
+ * If the max CPU id is out of bound, set it to -1 so it results in a
+ * CPU num of 0.
+ */
+ if (max_cpuid < 0 || max_cpuid > INT_MAX)
+ max_cpuid = -1;
+
+end:
+ /*
+ * Get the sysconf value as a last resort. Keep the highest number.
+ */
+ return __max(sysconf(_SC_NPROCESSORS_CONF), max_cpuid + 1);
+}
+
+/*
+ * 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;
}
projects / lttng-ust.git / blobdiff