[PATCH] drm/sysfs: Add drm class-wide attribute to get active device clients

[Adrián Larumbe]

Up to this day, all fdinfo-based GPU profilers must traverse the entire
/proc directory structure to find open DRM clients with fdinfo file
descriptors. This is inefficient and time-consuming.

This patch adds a new device class attribute that will install a sysfs file
per DRM device, which can be queried by profilers to get a list of PIDs for
their open clients. This file isn't human-readable, and it's meant to be
queried only by GPU profilers like gputop and nvtop.

Cc: Boris Brezillon <boris.brezillon at collabora.com>
Cc: Tvrtko Ursulin <tursulin at ursulin.net>
Cc: Christopher Healy <healych at amazon.com>
Signed-off-by: Adrián Larumbe <adrian.larumbe at collabora.com>
---
 drivers/gpu/drm/drm_internal.h       |  2 +-
 drivers/gpu/drm/drm_privacy_screen.c |  2 +-
 drivers/gpu/drm/drm_sysfs.c          | 89 ++++++++++++++++++++++------
 3 files changed, 74 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
index 2215baef9a3e..9a399b03d11c 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -145,7 +145,7 @@ bool drm_master_internal_acquire(struct drm_device *dev);
 void drm_master_internal_release(struct drm_device *dev);
 
 /* drm_sysfs.c */
-extern struct class *drm_class;
+extern struct class drm_class;
 
 int drm_sysfs_init(void);
 void drm_sysfs_destroy(void);
diff --git a/drivers/gpu/drm/drm_privacy_screen.c b/drivers/gpu/drm/drm_privacy_screen.c
index 6cc39e30781f..2fbd24ba5818 100644
--- a/drivers/gpu/drm/drm_privacy_screen.c
+++ b/drivers/gpu/drm/drm_privacy_screen.c
@@ -401,7 +401,7 @@ struct drm_privacy_screen *drm_privacy_screen_register(
 	mutex_init(&priv->lock);
 	BLOCKING_INIT_NOTIFIER_HEAD(&priv->notifier_head);
 
-	priv->dev.class = drm_class;
+	priv->dev.class = &drm_class;
 	priv->dev.type = &drm_privacy_screen_type;
 	priv->dev.parent = parent;
 	priv->dev.release = drm_privacy_screen_device_release;
diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
index a953f69a34b6..56ca9e22c720 100644
--- a/drivers/gpu/drm/drm_sysfs.c
+++ b/drivers/gpu/drm/drm_sysfs.c
@@ -58,8 +58,6 @@ static struct device_type drm_sysfs_device_connector = {
 	.name = "drm_connector",
 };
 
-struct class *drm_class;
-
 #ifdef CONFIG_ACPI
 static bool drm_connector_acpi_bus_match(struct device *dev)
 {
@@ -128,6 +126,62 @@ static const struct component_ops typec_connector_ops = {
 
 static CLASS_ATTR_STRING(version, S_IRUGO, "drm 1.1.0 20060810");
 
+static ssize_t clients_show(struct device *cd, struct device_attribute *attr, char *buf)
+{
+	struct drm_minor *minor = cd->driver_data;
+	struct drm_device *ddev = minor->dev;
+	struct drm_file *priv;
+	ssize_t offset = 0;
+	void *pid_buf;
+
+	if (minor->type != DRM_MINOR_RENDER)
+		return 0;
+
+	pid_buf = kvmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!pid_buf)
+		return 0;
+
+	mutex_lock(&ddev->filelist_mutex);
+	list_for_each_entry_reverse(priv, &ddev->filelist, lhead) {
+		struct pid *pid;
+
+		if (drm_WARN_ON(ddev, (PAGE_SIZE - offset) < sizeof(pid_t)))
+			break;
+
+		rcu_read_lock();
+		pid = rcu_dereference(priv->pid);
+		(*(pid_t *)(pid_buf + offset)) = pid_vnr(pid);
+		rcu_read_unlock();
+
+		offset += sizeof(pid_t);
+	}
+	mutex_unlock(&ddev->filelist_mutex);
+
+	if (offset < PAGE_SIZE)
+		(*(pid_t *)(pid_buf + offset)) = 0;
+
+	memcpy(buf, pid_buf, offset);
+
+	kvfree(pid_buf);
+
+	return offset;
+
+}
+static DEVICE_ATTR_RO(clients);
+
+static struct attribute *drm_device_attrs[] = {
+	&dev_attr_clients.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(drm_device);
+
+struct class drm_class = {
+	.name		= "drm",
+	.dev_groups	= drm_device_groups,
+};
+
+static bool drm_class_initialised;
+
 /**
  * drm_sysfs_init - initialize sysfs helpers
  *
@@ -142,18 +196,19 @@ int drm_sysfs_init(void)
 {
 	int err;
 
-	drm_class = class_create("drm");
-	if (IS_ERR(drm_class))
-		return PTR_ERR(drm_class);
+	err = class_register(&drm_class);
+	if (err)
+		return err;
 
-	err = class_create_file(drm_class, &class_attr_version.attr);
+	err = class_create_file(&drm_class, &class_attr_version.attr);
 	if (err) {
-		class_destroy(drm_class);
-		drm_class = NULL;
+		class_destroy(&drm_class);
 		return err;
 	}
 
-	drm_class->devnode = drm_devnode;
+	drm_class.devnode = drm_devnode;
+
+	drm_class_initialised = true;
 
 	drm_sysfs_acpi_register();
 	return 0;
@@ -166,12 +221,12 @@ int drm_sysfs_init(void)
  */
 void drm_sysfs_destroy(void)
 {
-	if (IS_ERR_OR_NULL(drm_class))
+	if (!drm_class_initialised)
 		return;
 	drm_sysfs_acpi_unregister();
-	class_remove_file(drm_class, &class_attr_version.attr);
-	class_destroy(drm_class);
-	drm_class = NULL;
+	class_remove_file(&drm_class, &class_attr_version.attr);
+	class_destroy(&drm_class);
+	drm_class_initialised = false;
 }
 
 static void drm_sysfs_release(struct device *dev)
@@ -372,7 +427,7 @@ int drm_sysfs_connector_add(struct drm_connector *connector)
 		return -ENOMEM;
 
 	device_initialize(kdev);
-	kdev->class = drm_class;
+	kdev->class = &drm_class;
 	kdev->type = &drm_sysfs_device_connector;
 	kdev->parent = dev->primary->kdev;
 	kdev->groups = connector_dev_groups;
@@ -550,7 +605,7 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
 			minor_str = "card%d";
 
 		kdev->devt = MKDEV(DRM_MAJOR, minor->index);
-		kdev->class = drm_class;
+		kdev->class = &drm_class;
 		kdev->type = &drm_sysfs_device_minor;
 	}
 
@@ -579,10 +634,10 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
  */
 int drm_class_device_register(struct device *dev)
 {
-	if (!drm_class || IS_ERR(drm_class))
+	if (!drm_class_initialised)
 		return -ENOENT;
 
-	dev->class = drm_class;
+	dev->class = &drm_class;
 	return device_register(dev);
 }
 EXPORT_SYMBOL_GPL(drm_class_device_register);

base-commit: 45c734fdd43db14444025910b4c59dd2b8be714a
-- 
2.44.0