#define __max(a,b) ((a)>(b)?(a):(b))
-static int num_possible_cpus_cache;
+static int possible_cpus_array_len_cache;
/*
- * 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
+ * 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.
*
- * 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.
+ * Returns the highest CPU id, or -1 on error.
*/
-int get_num_possible_cpus_fallback(void)
+int get_max_cpuid_from_sysfs(void)
+{
+ return _get_max_cpuid_from_sysfs("/sys/devices/system/cpu");
+}
+
+int _get_max_cpuid_from_sysfs(const char *path)
{
long max_cpuid = -1;
DIR *cpudir;
struct dirent *entry;
- cpudir = opendir("/sys/devices/system/cpu");
+ assert(path);
+
+ cpudir = opendir(path);
if (cpudir == NULL)
goto end;
max_cpuid = -1;
end:
+ return max_cpuid;
+}
+
+/*
+ * 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)
+{
/*
* Get the sysconf value as a last resort. Keep the highest number.
*/
- return __max(sysconf(_SC_NPROCESSORS_CONF), max_cpuid + 1);
+ return __max(sysconf(_SC_NPROCESSORS_CONF), get_max_cpuid_from_sysfs() + 1);
}
/*
* Returns the number of bytes read or -1 on error.
*/
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 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.
+ */
+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("/sys/devices/system/cpu/possible", O_RDONLY);
+ fd = open(path, O_RDONLY);
if (fd < 0)
goto end;
}
/*
- * 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;
char buf[LTTNG_UST_CPUMASK_SIZE];
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