MINOR: cpuset: centralize a reliable bound cpu detection

Till now the CPUs that were bound were only retrieved in
thread_cpus_enabled() in order to count the number of CPUs allowed,
and it relied on arch-specific code.

Let's slightly arrange this into ha_cpuset_detect_bound() that
reuses the ha_cpuset struct and the accompanying code. This makes
the code much clearer without having to carry along some arch-specific
stuff out of this area.

Note that the macos-specific code used in thread.c to only count
online CPUs but not retrieve a mask, so for now we can't infer
anything from it and can't implement it.

In addition and more importantly, this function is reliable in that
it will only return a value when the detection is accurate, and will
not return incomplete sets on operating systems where we don't have
an exact list, such as online CPUs.

include/haproxy/cpuset.h

@@ -48,6 +48,11 @@ void ha_cpuset_assign(struct hap_cpuset *dst, struct hap_cpuset *src);
  */
 int ha_cpuset_size(void);
 
+/* Detects CPUs that are bound to the current process. Returns the number of
+ * CPUs detected or 0 if the detection failed.
+ */
+int ha_cpuset_detect_bound(struct hap_cpuset *set);
+
 /* Returns true if at least one cpu-map directive was configured, otherwise
  * false.
  */

src/cpuset.c

@@ -147,6 +147,30 @@ int ha_cpuset_size()
 #endif
 }
 
+/* Detects CPUs that are bound to the current process. Returns the number of
+ * CPUs detected or 0 if the detection failed.
+ */
+int ha_cpuset_detect_bound(struct hap_cpuset *set)
+{
+	ha_cpuset_zero(set);
+
+	/* detect bound CPUs depending on the OS's API */
+	if (0
+#if defined(__linux__)
+	    || sched_getaffinity(0, sizeof(set->cpuset), &set->cpuset) != 0
+#elif defined(__FreeBSD__)
+	    || cpuset_getaffinity(CPU_LEVEL_CPUSET, CPU_WHICH_PID, -1, sizeof(set->cpuset), &set->cpuset) != 0
+#else
+	    || 1 // unhandled platform
+#endif
+	    ) {
+		/* detection failed */
+		return 0;
+	}
+
+	return ha_cpuset_count(set);
+}
+
 /* Returns true if at least one cpu-map directive was configured, otherwise
  * false.
  */