[PATCH v3 3/7] drivers/base/node: Add support to write node_states[] via sysfs

[Jagdish Gediya <jvgediya@linux.ibm.com>]

Current /sys/devices/system/node/* interface doesn't support
to write node_states[], however write support is needed in case
users want to set them manually e.g. when user want to override
default N_DEMOTION_TARGETS found by the kernel.

Rename existing _NODE_ATTR to _NODE_ATTR_RO and introduce new
_NODE_ATTR_RW which can be used for node_states[] which can
be written from sysfs.

It may be necessary to validate written values and take action
based on them in a state specific way so a callback 'write' is
introduced in 'struct node_attr'.

A new function demotion_targets_write() is added to validate
the input nodes for N_DEMOTION_TARGETS which should be subset
of N_MEMORY and to build new demotion list based on new nodes.

Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
---
 drivers/base/node.c | 62 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 49 insertions(+), 13 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 6eef22e6413e..e03eedbc421b 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -20,6 +20,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/swap.h>
 #include <linux/slab.h>
+#include <linux/migrate.h>
 
 static struct bus_type node_subsys = {
 	.name = "node",
@@ -1013,6 +1014,7 @@ void unregister_one_node(int nid)
 struct node_attr {
 	struct device_attribute attr;
 	enum node_states state;
+	int (*write)(nodemask_t nodes);
 };
 
 static ssize_t show_node_state(struct device *dev,
@@ -1024,23 +1026,57 @@ static ssize_t show_node_state(struct device *dev,
 			  nodemask_pr_args(&node_states[na->state]));
 }
 
-#define _NODE_ATTR(name, state) \
-	{ __ATTR(name, 0444, show_node_state, NULL), state }
+static ssize_t store_node_state(struct device *s,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	nodemask_t nodes;
+	struct node_attr *na = container_of(attr, struct node_attr, attr);
+
+	if (nodelist_parse(buf, nodes))
+		return -EINVAL;
+
+	if (na->write) {
+		if (na->write(nodes))
+			return -EINVAL;
+	} else {
+		node_states[na->state] = nodes;
+	}
+
+	return count;
+}
+
+static int demotion_targets_write(nodemask_t nodes)
+{
+	if (nodes_subset(nodes, node_states[N_MEMORY])) {
+		node_states[N_DEMOTION_TARGETS] = nodes;
+		set_migration_target_nodes();
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+#define _NODE_ATTR_RO(name, state) \
+	{ __ATTR(name, 0444, show_node_state, NULL), state, NULL }
+
+#define _NODE_ATTR_RW(name, state, write_fn) \
+	{ __ATTR(name, 0644, show_node_state, store_node_state), state, write_fn }
 
 static struct node_attr node_state_attr[] = {
-	[N_POSSIBLE] = _NODE_ATTR(possible, N_POSSIBLE),
-	[N_ONLINE] = _NODE_ATTR(online, N_ONLINE),
-	[N_NORMAL_MEMORY] = _NODE_ATTR(has_normal_memory, N_NORMAL_MEMORY),
+	[N_POSSIBLE] = _NODE_ATTR_RO(possible, N_POSSIBLE),
+	[N_ONLINE] = _NODE_ATTR_RO(online, N_ONLINE),
+	[N_NORMAL_MEMORY] = _NODE_ATTR_RO(has_normal_memory, N_NORMAL_MEMORY),
 #ifdef CONFIG_HIGHMEM
-	[N_HIGH_MEMORY] = _NODE_ATTR(has_high_memory, N_HIGH_MEMORY),
+	[N_HIGH_MEMORY] = _NODE_ATTR_RO(has_high_memory, N_HIGH_MEMORY),
 #endif
-	[N_MEMORY] = _NODE_ATTR(has_memory, N_MEMORY),
-	[N_CPU] = _NODE_ATTR(has_cpu, N_CPU),
-	[N_GENERIC_INITIATOR] = _NODE_ATTR(has_generic_initiator,
-					   N_GENERIC_INITIATOR),
-	[N_DEMOTION_TARGETS] = _NODE_ATTR(demotion_targets,
-					  N_DEMOTION_TARGETS),
-
+	[N_MEMORY] = _NODE_ATTR_RO(has_memory, N_MEMORY),
+	[N_CPU] = _NODE_ATTR_RO(has_cpu, N_CPU),
+	[N_GENERIC_INITIATOR] = _NODE_ATTR_RO(has_generic_initiator,
+					      N_GENERIC_INITIATOR),
+	[N_DEMOTION_TARGETS] = _NODE_ATTR_RW(demotion_targets,
+					     N_DEMOTION_TARGETS,
+					     demotion_targets_write),
 };
 
 static struct attribute *node_state_attrs[] = {
-- 
2.35.1