show isolated cpus in sysfs

After system bootup, there is no totally reliable way to see
which CPUs are isolated, because the kernel may modify the
CPUs specified on the isolcpus= kernel command line option.

Export the CPU list that actually got isolated in sysfs,
specifically in the file /sys/devices/system/cpu/isolated

This can be used by system management tools like libvirt,
openstack, and others to ensure proper placement of tasks.

Suggested-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Acked-by: Chris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index f160ea44a86d68a26b689b5ff7c5f0bcaf5ec74e..ea23ee7b545b17f10c8bed3d826b49de15a978b0 100644 (file)
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -265,6 +265,17 @@ static ssize_t print_cpus_offline(struct device *dev,
 }
 static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
 
+static ssize_t print_cpus_isolated(struct device *dev,
+                                 struct device_attribute *attr, char *buf)
+{
+       int n = 0, len = PAGE_SIZE-2;
+
+       n = scnprintf(buf, len, "%*pbl\n", cpumask_pr_args(cpu_isolated_map));
+
+       return n;
+}
+static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL);
+
 static void cpu_device_release(struct device *dev)
 {
        /*
@@ -431,6 +442,7 @@ static struct attribute *cpu_root_attrs[] = {
        &cpu_attrs[2].attr.attr,
        &dev_attr_kernel_max.attr,
        &dev_attr_offline.attr,
+       &dev_attr_isolated.attr,
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
        &dev_attr_modalias.attr,
 #endif