#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 <sys/types.h>
#include <urcu/compiler.h>
-#include "common/align.h"
#include "common/logging.h"
#include "common/smp.h"
-static int num_possible_cpus_cache;
-
-#if (defined(__GLIBC__) || defined( __UCLIBC__))
-int get_num_possible_cpus_fallback(void)
-{
- /* 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.
- */
- return sysconf(_SC_NPROCESSORS_CONF);
-}
+#define __max(a,b) ((a)>(b)?(a):(b))
-#else
+static int possible_cpus_array_len_cache;
/*
- * 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.
+ * 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.
*
- * 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.
+ * 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.
*/
-
-#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;
+ long max_cpuid = -1;
+
DIR *cpudir;
struct dirent *entry;
goto end;
/*
- * Count the number of directories named "cpu" followed by and
- * integer. This is the same strategy as glibc uses.
+ * 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;
- unsigned long cpu_num;
+ long cpu_id;
- cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
- if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
+ cpu_id = strtol(entry->d_name + 3, &endptr, 10);
+ if ((cpu_id < LONG_MAX) && (endptr != entry->d_name + 3)
&& (*endptr == '\0')) {
- count++;
+ if (cpu_id > max_cpuid)
+ max_cpuid = cpu_id;
}
}
}
+ /*
+ * 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 fallback. Keep the highest number.
+ * Get the sysconf value as a last resort. Keep the highest number.
*/
- return __max(sysconf(_SC_NPROCESSORS_CONF), count);
+ return __max(sysconf(_SC_NPROCESSORS_CONF), max_cpuid + 1);
}
-#endif
/*
* Get the CPU possible mask string from sysfs.
{
ssize_t bytes_read = 0;
size_t total_bytes_read = 0;
- int fd = 0;
+ int fd = -1, ret = -1;
if (buf == NULL)
- return -1;
+ goto end;
fd = open("/sys/devices/system/cpu/possible", O_RDONLY);
if (fd < 0)
- return -1;
+ goto end;
do {
bytes_read = read(fd, buf + total_bytes_read,
if (errno == EINTR) {
continue; /* retry operation */
} else {
- return -1;
+ goto end;
}
}
assert(total_bytes_read <= max_bytes);
} while (max_bytes > total_bytes_read && bytes_read > 0);
- if (close(fd))
- PERROR("close");
-
/*
* Make sure the mask read is a null terminated string.
*/
else
buf[max_bytes - 1] = '\0';
- return total_bytes_read;
+ 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.
+ * Get the highest CPU id from a 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.
+ * Returns the highest CPU id from the mask or -1 on error.
*/
-int get_num_possible_cpus_from_mask(const char *pmask, size_t len)
+int get_max_cpuid_from_mask(const char *pmask, size_t len)
{
ssize_t i;
unsigned long cpu_index;
* CPUs.
*/
if ((&pmask[i] != endptr) && (cpu_index < INT_MAX))
- return (int) cpu_index + 1;
+ return (int) cpu_index;
error:
- return 0;
+ return -1;
}
-static void _get_num_possible_cpus(void)
+static void update_possible_cpus_array_len_cache(void)
{
int ret;
- int buf_len = LTTNG_UST_PAGE_SIZE;
- char buf[buf_len];
+ 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, buf_len);
+ 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)
+ 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. */
if (ret < 1)
return;
- num_possible_cpus_cache = ret;
+ possible_cpus_array_len_cache = ret;
}
/*
- * Returns the total number of CPUs in the system. If the cache is not yet
- * initialized, get the value from "/sys/devices/system/cpu/possible" or
- * fallback to sysconf and cache it.
+ * 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 num_possible_cpus(void)
+int get_possible_cpus_array_len(void)
{
- if (caa_unlikely(!num_possible_cpus_cache))
- _get_num_possible_cpus();
+ if (caa_unlikely(!possible_cpus_array_len_cache))
+ update_possible_cpus_array_len_cache();
- return num_possible_cpus_cache;
+ return possible_cpus_array_len_cache;
}
projects / lttng-ust.git / blobdiff