Implement a new sysfs file, nr_producers, under the producers/
directory.  The file will be used for generating directories for each
report producer, in a manner that is similar to the nr_kdamonds file.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 75701ed662222..d3a7cb170975a 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -2983,6 +2983,7 @@ static const struct kobj_type damon_sysfs_kdamonds_ktype = {
 
 struct damon_sysfs_producers {
 	struct kobject kobj;
+	int nr;
 };
 
 static struct damon_sysfs_producers *damon_sysfs_producers_alloc(void)
@@ -2990,12 +2991,62 @@ static struct damon_sysfs_producers *damon_sysfs_producers_alloc(void)
 	return kzalloc_obj(struct damon_sysfs_producers);
 }
 
+static void damon_sysfs_producers_rm_dirs(
+		struct damon_sysfs_producers *producers)
+{
+	producers->nr = 0;
+}
+
+static int damon_sysfs_producers_add_dirs(
+		struct damon_sysfs_producers *producers, int nr_producers)
+{
+	damon_sysfs_producers_rm_dirs(producers);
+	producers->nr = nr_producers;
+	return 0;
+}
+
+static ssize_t nr_producers_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_producers *producers = container_of(kobj,
+			struct damon_sysfs_producers, kobj);
+
+	return sysfs_emit(buf, "%d\n", producers->nr);
+}
+
+static ssize_t nr_producers_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_producers *producers;
+	int nr, err = kstrtoint(buf, 0, &nr);
+
+	if (err)
+		return err;
+	if (nr < 0)
+		return -EINVAL;
+
+	producers = container_of(kobj, struct damon_sysfs_producers, kobj);
+
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return -EBUSY;
+	err = damon_sysfs_producers_add_dirs(producers, nr);
+	mutex_unlock(&damon_sysfs_lock);
+	if (err)
+		return err;
+
+	return count;
+}
+
 static void damon_sysfs_producers_release(struct kobject *kobj)
 {
 	kfree(container_of(kobj, struct damon_sysfs_producers, kobj));
 }
 
+static struct kobj_attribute damon_sysfs_producers_nr_attr =
+__ATTR_RW_MODE(nr_producers, 0600);
+
 static struct attribute *damon_sysfs_producers_attrs[] = {
+	&damon_sysfs_producers_nr_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_producers);
-- 
2.47.3