--- /dev/null
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
+ */
+
+#define _LGPL_SOURCE
+#include <assert.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <side/macros.h>
+
+#include "smp.h"
+
+#define __max(a,b) ((a)>(b)?(a):(b))
+
+#define SIDE_CPUMASK_SIZE 4096
+
+static int possible_cpus_array_len_cache;
+
+static
+int _get_max_cpuid_from_sysfs(const char *path)
+{
+ long max_cpuid = -1;
+
+ DIR *cpudir;
+ struct dirent *entry;
+
+ assert(path);
+
+ cpudir = opendir(path);
+ if (cpudir == NULL)
+ goto end;
+
+ /*
+ * Iterate on all directories named "cpu" followed by an integer.
+ */
+ 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:
+ return max_cpuid;
+}
+
+/*
+ * Get the highest CPU id from sysfs.
+ *
+ * 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.
+ *
+ * Returns the highest CPU id, or -1 on error.
+ */
+static
+int get_max_cpuid_from_sysfs(void)
+{
+ return _get_max_cpuid_from_sysfs("/sys/devices/system/cpu");
+}
+
+/*
+ * 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.
+ */
+static
+int get_num_possible_cpus_fallback(void)
+{
+ /*
+ * Get the sysconf value as a last resort. Keep the highest number.
+ */
+ return __max(sysconf(_SC_NPROCESSORS_CONF), get_max_cpuid_from_sysfs() + 1);
+}
+
+/*
+ * Get a CPU 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.
+ * path: file path to read the mask from.
+ *
+ * Returns the number of bytes read or -1 on error.
+ */
+static
+int get_cpu_mask_from_sysfs(char *buf, size_t max_bytes, const char *path)
+{
+ ssize_t bytes_read = 0;
+ size_t total_bytes_read = 0;
+ int fd = -1, ret = -1;
+
+ assert(path);
+
+ if (buf == NULL)
+ goto end;
+
+ fd = open(path, 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 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.
+ */
+static
+int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)
+{
+ return get_cpu_mask_from_sysfs(buf, max_bytes,
+ "/sys/devices/system/cpu/possible");
+}
+
+/*
+ * Get the highest CPU id from a CPU mask.
+ *
+ * pmask: the mask to parse.
+ * len: the len of the mask excluding '\0'.
+ *
+ * Returns the highest CPU id from the mask or -1 on error.
+ */
+static
+int get_max_cpuid_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 ((&pmask[i] != endptr) && (cpu_index < INT_MAX))
+ return (int) cpu_index;
+
+error:
+ return -1;
+}
+
+static void update_possible_cpus_array_len_cache(void)
+{
+ char buf[SIDE_CPUMASK_SIZE];
+ int ret;
+
+ /* Get the possible cpu mask from sysfs, fallback to sysconf. */
+ ret = get_possible_cpu_mask_from_sysfs((char *) &buf, SIDE_CPUMASK_SIZE);
+ if (ret <= 0)
+ goto fallback;
+
+ /* Parse the possible cpu mask, on failure fallback to sysconf. */
+ ret = get_max_cpuid_from_mask((char *) &buf, ret);
+ if (ret >= 0) {
+ /* Add 1 to convert from max cpuid to an array len. */
+ ret++;
+ 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;
+
+ possible_cpus_array_len_cache = ret;
+}
+
+/*
+ * Returns the length of an array that could contain a per-CPU element for each
+ * possible CPU id for the lifetime of the process.
+ *
+ * We currently assume CPU ids are contiguous up the maximum CPU id.
+ *
+ * If the cache is not yet initialized, get the value from
+ * "/sys/devices/system/cpu/possible" or fallback to sysconf and cache it.
+ *
+ * If all methods fail, don't populate the cache and return 0.
+ */
+int get_possible_cpus_array_len(void)
+{
+ if (side_unlikely(!possible_cpus_array_len_cache))
+ update_possible_cpus_array_len_cache();
+
+ return possible_cpus_array_len_cache;
+}
projects / libside.git / commitdiff
