[RFC 4/5] cpu/cpuns: Make sysfs CPU namespace aware

["Pratik R. Sampat" <psampat@xxxxxxxxxxxxx>]

The commit adds support to sysfs files like online, offline, present to
be CPU namespace context aware. It presents virtualized CPU information
which is coherent to the cgroup cpuset restrictions that are set upon
the tasks.

Signed-off-by: Pratik R. Sampat <psampat@xxxxxxxxxxxxx>
---
 drivers/base/cpu.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 5ef14db97904..1487b23e5472 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -20,6 +20,7 @@
 #include <linux/tick.h>
 #include <linux/pm_qos.h>
 #include <linux/sched/isolation.h>
+#include <linux/cpu_namespace.h>
 
 #include "base.h"
 
@@ -203,6 +204,24 @@ struct cpu_attr {
 	const struct cpumask *const map;
 };
 
+#ifdef CONFIG_CPU_NS
+static ssize_t show_cpuns_cpus_attr(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct cpu_attr *ca = container_of(attr, struct cpu_attr, attr);
+
+	if (current->nsproxy->cpu_ns == &init_cpu_ns)
+		return cpumap_print_to_pagebuf(true, buf, ca->map);
+
+	return cpumap_print_to_pagebuf(true, buf,
+				       &current->nsproxy->cpu_ns->v_cpuset_cpus);
+}
+
+#define _CPU_CPUNS_ATTR(name, map) \
+	{ __ATTR(name, 0444, show_cpuns_cpus_attr, NULL), map }
+#endif
+
 static ssize_t show_cpus_attr(struct device *dev,
 			      struct device_attribute *attr,
 			      char *buf)
@@ -217,9 +236,14 @@ static ssize_t show_cpus_attr(struct device *dev,
 
 /* Keep in sync with cpu_subsys_attrs */
 static struct cpu_attr cpu_attrs[] = {
+#ifdef CONFIG_CPU_NS
+	_CPU_CPUNS_ATTR(online, &__cpu_online_mask),
+	_CPU_CPUNS_ATTR(present, &__cpu_present_mask),
+#else
 	_CPU_ATTR(online, &__cpu_online_mask),
-	_CPU_ATTR(possible, &__cpu_possible_mask),
 	_CPU_ATTR(present, &__cpu_present_mask),
+#endif
+	_CPU_ATTR(possible, &__cpu_possible_mask),
 };
 
 /*
@@ -244,7 +268,16 @@ static ssize_t print_cpus_offline(struct device *dev,
 	/* display offline cpus < nr_cpu_ids */
 	if (!alloc_cpumask_var(&offline, GFP_KERNEL))
 		return -ENOMEM;
+#ifdef CONFIG_CPU_NS
+	if (current->nsproxy->cpu_ns == &init_cpu_ns) {
+		cpumask_andnot(offline, cpu_possible_mask, cpu_online_mask);
+	} else {
+		cpumask_andnot(offline, cpu_possible_mask,
+			       &current->nsproxy->cpu_ns->v_cpuset_cpus);
+	}
+#else
 	cpumask_andnot(offline, cpu_possible_mask, cpu_online_mask);
+#endif
 	len += sysfs_emit_at(buf, len, "%*pbl", cpumask_pr_args(offline));
 	free_cpumask_var(offline);
 
-- 
2.31.1