mm/damon/sysfs: add a file for listing available monitoring ops

DAMON programming interface users can know if specific monitoring ops set
is registered or not using 'damon_is_registered_ops()', but there is no
such method for the user space.  To help the case, this commit adds a new
DAMON sysfs file called 'avail_operations' under each context directory
for listing available monitoring ops.  Reading the file will list each
registered monitoring ops on each line.

Link: https://lkml.kernel.org/r/20220426203843.45238-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 48e434c..6ad6364 100644 (file)
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1810,6 +1810,21 @@ static void damon_sysfs_context_rm_dirs(struct damon_sysfs_context *context)
        kobject_put(&context->schemes->kobj);
 }
 
+static ssize_t avail_operations_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       enum damon_ops_id id;
+       int len = 0;
+
+       for (id = 0; id < NR_DAMON_OPS; id++) {
+               if (!damon_is_registered_ops(id))
+                       continue;
+               len += sysfs_emit_at(buf, len, "%s\n",
+                               damon_sysfs_ops_strs[id]);
+       }
+       return len;
+}
+
 static ssize_t operations_show(struct kobject *kobj,
                struct kobj_attribute *attr, char *buf)
 {
@@ -1840,10 +1855,14 @@ static void damon_sysfs_context_release(struct kobject *kobj)
        kfree(container_of(kobj, struct damon_sysfs_context, kobj));
 }
 
+static struct kobj_attribute damon_sysfs_context_avail_operations_attr =
+               __ATTR_RO_MODE(avail_operations, 0400);
+
 static struct kobj_attribute damon_sysfs_context_operations_attr =
                __ATTR_RW_MODE(operations, 0600);
 
 static struct attribute *damon_sysfs_context_attrs[] = {
+       &damon_sysfs_context_avail_operations_attr.attr,
        &damon_sysfs_context_operations_attr.attr,
        NULL,
 };