From 5de7c318804a7b1edce8562d4891b4c74aac0677 Mon Sep 17 00:00:00 2001 From: Michael Jeanson 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. Signed-off-by: Michael Jeanson Signed-off-by: Mathieu Desnoyers --- 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 + * Copyright (C) 2019 Michael Jeanson * * 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 +#include +#include +#include +#include + +#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 -- 2.34.1