Introduce a new DAMON sysfs file for letting users setup the target
memory cgroup of the belonging memory cgroup attribute monitoring.  The
file is named 'filter', located under the probe filter directory.  Users
can set the target memory cgroup by writing the path to the memory
cgroup from the cgroup mount point to the file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index e4dbf85feadc2..2b68e1a7de451 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -756,6 +756,7 @@ struct damon_sysfs_filter {
 	enum damon_filter_type type;
 	bool matching;
 	bool allow;
+	char *path;
 };
 
 static struct damon_sysfs_filter *damon_sysfs_filter_alloc(void)
@@ -774,6 +775,10 @@ damon_sysfs_filter_type_names[] = {
 		.type = DAMON_FILTER_TYPE_ANON,
 		.name = "anon",
 	},
+	{
+		.type = DAMON_FILTER_TYPE_MEMCG,
+		.name = "memcg",
+	},
 };
 
 static ssize_t type_show(struct kobject *kobj,
@@ -862,11 +867,46 @@ static ssize_t allow_store(struct kobject *kobj,
 	return count;
 }
 
+static ssize_t path_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+	int len;
+
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return -EBUSY;
+	len = sysfs_emit(buf, "%s\n", filter->path ? filter->path : "");
+	mutex_unlock(&damon_sysfs_lock);
+	return len;
+}
+
+static ssize_t path_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+	char *path = kmalloc_objs(*path, size_add(count, 1));
+
+	if (!path)
+		return -ENOMEM;
+	strscpy(path, buf, size_add(count, 1));
+	if (!mutex_trylock(&damon_sysfs_lock)) {
+		kfree(path);
+		return -EBUSY;
+	}
+	kfree(filter->path);
+	filter->path = path;
+	mutex_unlock(&damon_sysfs_lock);
+	return count;
+}
+
 static void damon_sysfs_filter_release(struct kobject *kobj)
 {
 	struct damon_sysfs_filter *filter = container_of(kobj,
 			struct damon_sysfs_filter, kobj);
 
+	kfree(filter->path);
 	kfree(filter);
 }
 
@@ -879,10 +919,14 @@ static struct kobj_attribute damon_sysfs_filter_matching_attr =
 static struct kobj_attribute damon_sysfs_filter_allow_attr =
 		__ATTR_RW_MODE(allow, 0600);
 
+static struct kobj_attribute damon_sysfs_filter_path_attr =
+		__ATTR_RW_MODE(path, 0600);
+
 static struct attribute *damon_sysfs_filter_attrs[] = {
 	&damon_sysfs_filter_type_attr.attr,
 	&damon_sysfs_filter_matching_attr.attr,
 	&damon_sysfs_filter_allow_attr.attr,
+	&damon_sysfs_filter_path_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_filter);
-- 
2.47.3