mm/damon/sysfs-schemes: support target damos filter

Extend DAMON sysfs interface to support the DAMON monitoring target based
DAMOS filter. Users can use it via writing 'target' to the filter's
'type' file and specifying the index of the target from the corresponding
DAMON context's monitoring targets list to 'target_idx' sysfs file.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: SeongJae Park <[e-mail]>
Cc: Brendan Higgins <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/damon/sysfs-schemes.c

···
 	bool matching;
 	char *memcg_path;
 	struct damon_addr_range addr_range;
+	int target_idx;
 };
 
 static struct damon_sysfs_scheme_filter *damon_sysfs_scheme_filter_alloc(void)
···
 	"anon",
 	"memcg",
 	"addr",
+	"target",
 };
 
 static ssize_t type_show(struct kobject *kobj,
···
 	return err ? err : count;
 }
 
+static ssize_t damon_target_idx_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_scheme_filter *filter = container_of(kobj,
+			struct damon_sysfs_scheme_filter, kobj);
+
+	return sysfs_emit(buf, "%d\n", filter->target_idx);
+}
+
+static ssize_t damon_target_idx_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_scheme_filter *filter = container_of(kobj,
+			struct damon_sysfs_scheme_filter, kobj);
+	int err = kstrtoint(buf, 0, &filter->target_idx);
+
+	return err ? err : count;
+}
+
 static void damon_sysfs_scheme_filter_release(struct kobject *kobj)
 {
 	struct damon_sysfs_scheme_filter *filter = container_of(kobj,
···
 static struct kobj_attribute damon_sysfs_scheme_filter_addr_end_attr =
 		__ATTR_RW_MODE(addr_end, 0600);
 
+static struct kobj_attribute damon_sysfs_scheme_filter_damon_target_idx_attr =
+		__ATTR_RW_MODE(damon_target_idx, 0600);
+
 static struct attribute *damon_sysfs_scheme_filter_attrs[] = {
 	&damon_sysfs_scheme_filter_type_attr.attr,
 	&damon_sysfs_scheme_filter_matching_attr.attr,
 	&damon_sysfs_scheme_filter_memcg_path_attr.attr,
 	&damon_sysfs_scheme_filter_addr_start_attr.attr,
 	&damon_sysfs_scheme_filter_addr_end_attr.attr,
+	&damon_sysfs_scheme_filter_damon_target_idx_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_scheme_filter);
···
 				return -EINVAL;
 			}
 			filter->addr_range = sysfs_filter->addr_range;
+		} else if (filter->type == DAMOS_FILTER_TYPE_TARGET) {
+			filter->target_idx = sysfs_filter->target_idx;
 		}
 
 		damos_add_filter(scheme, filter);