driver-core/cpu: Expose hotpluggability to the rest of the kernel

When architectures register CPUs, they indicate whether the CPU allows
hotplugging; notably, x86 and ARM don't allow hotplugging CPU 0.
Userspace can easily query the hotpluggability of a CPU via sysfs;
however, the kernel has no convenient way of accessing that property in
an architecture-independent way.  While the kernel can simply try it and
see, some code needs to distinguish between "hotplug failed" and
"hotplug has no hope of working on this CPU"; for example, rcutorture's
CPU hotplug tests want to avoid drowning out real hotplug failures with
expected failures.

Expose this property via a new cpu_is_hotpluggable function, so that the
rest of the kernel can access it in an architecture-independent way.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 251acea..3991502 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -247,6 +247,13 @@ struct sys_device *get_cpu_sysdev(unsigned cpu)
 }
 EXPORT_SYMBOL_GPL(get_cpu_sysdev);
 
+bool cpu_is_hotpluggable(unsigned cpu)
+{
+	struct sys_device *dev = get_cpu_sysdev(cpu);
+	return dev && container_of(dev, struct cpu, sysdev)->hotpluggable;
+}
+EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
+
 int __init cpu_dev_init(void)
 {
 	int err;