fix: num_possible_cpus() with hot-unplugged CPUs

[lttng-ust.git] / src / common / smp.h

diff --git a/src/common/smp.h b/src/common/smp.h
index 5f81094fc802c7f6559d876c03ae6af6f4be13a4..b6dd5707819af414a4c4a203e1e3d998ad983cf3 100644 (file)
--- a/src/common/smp.h
+++ b/src/common/smp.h
@@ -7,11 +7,43 @@
 #ifndef _UST_COMMON_SMP_H
 #define _UST_COMMON_SMP_H
 
+/*
+ * 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)
+       __attribute__((visibility("hidden")));
+
+/*
+ * Get the number of possible CPUs in the system from either
+ * sysconf(_SC_NPROCESSORS_CONF) or some other mechanism depending on the libc.
+ *
+ * Returns the number of possible CPUs in the system or 0 on error.
+ */
+int get_num_possible_cpus_fallback(void)
+       __attribute__((visibility("hidden")));
+
+/*
+ * 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)
+       __attribute__((visibility("hidden")));
+
 /*
  * Returns the total number of CPUs in the system. If the cache is not yet
- * initialized, get the value from the system through sysconf and cache it.
+ * initialized, get the value from "/sys/devices/system/cpu/possible" or
+ * fallback to sysconf and cache it.
  *
- * If the sysconf call fails, don't populate the cache and return 0.
+ * If all methods fail, don't populate the cache and return 0.
  */
 int num_possible_cpus(void)
        __attribute__((visibility("hidden")));