src/compat-smp.h

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
   6  */
   7
   8 #include <assert.h>
   9 #include <ctype.h>
  10 #include <dirent.h>
  11 #include <errno.h>
  12 #include <fcntl.h>
  13 #include <limits.h>
  14 #include <pthread.h>
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <string.h>
  18 #include <unistd.h>
  19
  20 #include <urcu/compiler.h>
  21
  22 #define URCU_CPUMASK_SIZE 4096
  23
  24 #if defined(HAVE_SYSCONF)
  25 static inline int get_num_possible_cpus_sysconf(void)
  26 {
  27         return sysconf(_SC_NPROCESSORS_CONF);
  28 }
  29 #else
  30 /*
  31  * On platforms without sysconf(), always return -1.
  32  */
  33 static inline int get_num_possible_cpus_sysconf(void)
  34 {
  35         return -1;
  36 }
  37 #endif
  38
  39 #ifdef __linux__
  40 /*
  41  * Get the highest CPU id from sysfs.
  42  *
  43  * Iterate on all the folders in "/sys/devices/system/cpu" that start with
  44  * "cpu" followed by an integer, keep the highest CPU id encountered during
  45  * this iteration and add 1 to get a number of CPUs.
  46  *
  47  * Returns the highest CPU id, or -1 on error.
  48  */
  49 static inline int _get_max_cpuid_from_sysfs(const char *path)
  50 {
  51         long max_cpuid = -1;
  52
  53         DIR *cpudir;
  54         struct dirent *entry;
  55
  56         assert(path);
  57
  58         cpudir = opendir(path);
  59         if (cpudir == NULL)
  60                 goto end;
  61
  62         /*
  63          * Iterate on all directories named "cpu" followed by an integer.
  64          */
  65         while ((entry = readdir(cpudir))) {
  66                 if (entry->d_type == DT_DIR &&
  67                         strncmp(entry->d_name, "cpu", 3) == 0) {
  68
  69                         char *endptr;
  70                         long cpu_id;
  71
  72                         cpu_id = strtol(entry->d_name + 3, &endptr, 10);
  73                         if ((cpu_id < LONG_MAX) && (endptr != entry->d_name + 3)
  74                                         && (*endptr == '\0')) {
  75                                 if (cpu_id > max_cpuid)
  76                                         max_cpuid = cpu_id;
  77                         }
  78                 }
  79         }
  80
  81         if (closedir(cpudir))
  82                 perror("closedir");
  83
  84         /*
  85          * If the max CPU id is out of bound, set it to -1 so it results in a
  86          * CPU num of 0.
  87          */
  88         if (max_cpuid < 0 || max_cpuid > INT_MAX)
  89                 max_cpuid = -1;
  90
  91 end:
  92         return max_cpuid;
  93 }
  94
  95 static inline int get_max_cpuid_from_sysfs(void)
  96 {
  97         return _get_max_cpuid_from_sysfs("/sys/devices/system/cpu");
  98 }
  99
 100
 101 /*
 102  * As a fallback to parsing the CPU mask in "/sys/devices/system/cpu/possible",
 103  * iterate on all the folders in "/sys/devices/system/cpu" that start with
 104  * "cpu" followed by an integer, keep the highest CPU id encountered during
 105  * this iteration and add 1 to get a number of CPUs.
 106  *
 107  * Then get the value from sysconf(_SC_NPROCESSORS_CONF) as a fallback and
 108  * return the highest one.
 109  *
 110  * On Linux, using the value from sysconf can be unreliable since the way it
 111  * counts CPUs varies between C libraries and even between versions of the same
 112  * library. If we used it directly, getcpu() could return a value greater than
 113  * this sysconf, in which case the arrays indexed by processor would overflow.
 114  *
 115  * As another example, the MUSL libc implementation of the _SC_NPROCESSORS_CONF
 116  * sysconf does not return the number of configured CPUs in the system but
 117  * relies on the cpu affinity mask of the current task.
 118  *
 119  * Returns 0 or less on error.
 120  */
 121 static inline int get_num_possible_cpus_fallback(void)
 122 {
 123         /*
 124          * Get the sysconf value as a last resort. Keep the highest number.
 125          */
 126         return caa_max(get_num_possible_cpus_sysconf(), get_max_cpuid_from_sysfs() + 1);
 127 }
 128
 129 /*
 130  * Get a CPU mask string from sysfs.
 131  *
 132  * buf: the buffer where the mask will be read.
 133  * max_bytes: the maximum number of bytes to write in the buffer.
 134  * path: file path to read the mask from.
 135  *
 136  * Returns the number of bytes read or -1 on error.
 137  */
 138 static inline int get_cpu_mask_from_sysfs(char *buf, size_t max_bytes, const char *path)
 139 {
 140         ssize_t bytes_read = 0;
 141         size_t total_bytes_read = 0;
 142         int fd = -1, ret = -1;
 143
 144         assert(path);
 145
 146         if (buf == NULL)
 147                 goto end;
 148
 149         fd = open(path, O_RDONLY);
 150         if (fd < 0)
 151                 goto end;
 152
 153         do {
 154                 bytes_read = read(fd, buf + total_bytes_read,
 155                                 max_bytes - total_bytes_read);
 156
 157                 if (bytes_read < 0) {
 158                         if (errno == EINTR) {
 159                                 continue;       /* retry operation */
 160                         } else {
 161                                 goto end;
 162                         }
 163                 }
 164
 165                 total_bytes_read += bytes_read;
 166                 assert(total_bytes_read <= max_bytes);
 167         } while (max_bytes > total_bytes_read && bytes_read != 0);
 168
 169         /*
 170          * Make sure the mask read is a null terminated string.
 171          */
 172         if (total_bytes_read < max_bytes)
 173                 buf[total_bytes_read] = '\0';
 174         else
 175                 buf[max_bytes - 1] = '\0';
 176
 177         if (total_bytes_read > INT_MAX)
 178                 goto end;
 179
 180         ret = (int) total_bytes_read;
 181
 182 end:
 183         if (fd >= 0 && close(fd) < 0)
 184                 perror("close");
 185
 186         return ret;
 187 }
 188
 189 /*
 190  * Get the CPU possible mask string from sysfs.
 191  *
 192  * buf: the buffer where the mask will be read.
 193  * max_bytes: the maximum number of bytes to write in the buffer.
 194  *
 195  * Returns the number of bytes read or -1 on error.
 196  */
 197 static inline int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)
 198 {
 199         return get_cpu_mask_from_sysfs(buf, max_bytes,
 200                         "/sys/devices/system/cpu/possible");
 201 }
 202
 203 /*
 204  * Get the highest CPU id from the possible CPU mask.
 205  *
 206  * pmask: the mask to parse.
 207  * len: the len of the mask excluding '\0'.
 208  *
 209  * Returns the highest CPU id from the mask or -1 on error.
 210  */
 211 static inline int get_max_cpuid_from_mask(const char *pmask, size_t len)
 212 {
 213         ssize_t i;
 214         unsigned long cpu_index;
 215         char *endptr;
 216
 217         /* We need at least one char to read */
 218         if (len < 1)
 219                 goto error;
 220
 221         /* Start from the end to read the last CPU index. */
 222         for (i = len - 1; i > 0; i--) {
 223                 /* Break when we hit the first separator. */
 224                 if ((pmask[i] == ',') || (pmask[i] == '-')) {
 225                         i++;
 226                         break;
 227                 }
 228         }
 229
 230         cpu_index = strtoul(&pmask[i], &endptr, 10);
 231
 232         if ((&pmask[i] != endptr) && (cpu_index < INT_MAX))
 233                 return (int) cpu_index;
 234
 235 error:
 236         return -1;
 237 }
 238
 239 /*
 240  * On Linux try sysfs first and fallback to sysconf.
 241  */
 242 static inline int get_possible_cpus_array_len(void)
 243 {
 244         int ret;
 245         char buf[URCU_CPUMASK_SIZE];
 246
 247         /* Get the possible cpu mask from sysfs, fallback to sysconf. */
 248         ret = get_possible_cpu_mask_from_sysfs((char *) &buf, URCU_CPUMASK_SIZE);
 249         if (ret <= 0)
 250                 goto fallback;
 251
 252         /* Parse the possible cpu mask, on failure fallback to sysconf. */
 253         ret = get_max_cpuid_from_mask((char *) &buf, ret);
 254         if (ret >= 0) {
 255                 /* Add 1 to convert from max cpuid to an array len. */
 256                 ret++;
 257                 goto end;
 258         }
 259
 260 fallback:
 261         /* Fallback to sysconf. */
 262         ret = get_num_possible_cpus_fallback();
 263
 264 end:
 265         return ret;
 266 }
 267 #else
 268 /*
 269  * On other platforms, only use sysconf.
 270  */
 271 static inline int get_possible_cpus_array_len(void)
 272 {
 273         return get_num_possible_cpus_sysconf();
 274 }
 275 #endif