compat: work around broken _SC_NPROCESSORS_CONF on MUSL libc

On MUSL libc the _SC_NPROCESSORS_CONF sysconf will report the number of
CPUs allocated to the task based on the affinity mask instead of the
total number of CPUs configured on the system.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/libringbuffer/smp.c b/libringbuffer/smp.c
index 9e7114be8a40f3349b8a8942131f440ce0514311..656a75da2787a40d6ac1188263863069f42745cd 100644 (file)
--- a/libringbuffer/smp.c
+++ b/libringbuffer/smp.c
@@ -2,6 +2,7 @@
  * libringbuffer/smp.c
  *
  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -26,6 +27,7 @@
 
 int __num_possible_cpus;
 
+#if (defined(__GLIBC__) || defined( __UCLIBC__))
 void _get_num_possible_cpus(void)
 {
        int result;
@@ -43,3 +45,67 @@ void _get_num_possible_cpus(void)
                return;
        __num_possible_cpus = result;
 }
+
+#else
+
+/*
+ * 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.
+ *
+ * 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.
+ */
+
+#include <dirent.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#define __max(a,b) ((a)>(b)?(a):(b))
+
+void _get_num_possible_cpus(void)
+{
+       int result, count = 0;
+       DIR *cpudir;
+       struct dirent *entry;
+
+       cpudir = opendir("/sys/devices/system/cpu");
+       if (cpudir == NULL)
+               goto end;
+
+       /*
+        * Count the number of directories named "cpu" followed by and
+        * integer. This is the same strategy as glibc uses.
+        */
+       while ((entry = readdir(cpudir))) {
+               if (entry->d_type == DT_DIR &&
+                       strncmp(entry->d_name, "cpu", 3) == 0) {
+
+                       char *endptr;
+                       unsigned long cpu_num;
+
+                       cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
+                       if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
+                                       && (*endptr == '\0')) {
+                               count++;
+                       }
+               }
+       }
+
+end:
+       /*
+        * Get the sysconf value as a fallback. Keep the highest number.
+        */
+       result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
+
+       /*
+        * If both methods failed, don't store the value.
+        */
+       if (result < 1)
+               return;
+       __num_possible_cpus = result;
+}
+#endif