--- /dev/null
+From 5de7c318804a7b1edce8562d4891b4c74aac0677 Mon Sep 17 00:00:00 2001
+From: Michael Jeanson <mjeanson@efficios.com>
+Date: Wed, 20 Mar 2019 11:07:35 -0400
+Subject: [PATCH] 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.
+
+Upstream-Status: Accepted [1] [5de7c318804a7b1edce8562d4891b4c74aac0677]
+[1] https://lists.lttng.org/pipermail/lttng-dev/2019-March/028616.html
+
+Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
+Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+---
+ libringbuffer/smp.c | 66 +++++++++++++++++++++++++++++++++++++++++++++
+ 1 file changed, 66 insertions(+)
+
+diff --git a/libringbuffer/smp.c b/libringbuffer/smp.c
+index 9e7114be..656a75da 100644
+--- 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
+--
+2.17.1
+
