[PATCH v2 1/1] drm: Add ioctl for querying a DRM device's list of open client PIDs

[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 DRM ioctl that allows users to obtain a list of PIDs
for clients who have opened the DRM device. Output from the ioctl isn't
human-readable, and it's meant to be retrieved only by GPU profilers like
gputop and nvtop.

Cc: Rob Clark <robdclark@xxxxxxxxx>
Cc: Tvrtko Ursulin <tursulin@xxxxxxxxxxx>
Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_internal.h |  1 +
 drivers/gpu/drm/drm_ioctl.c    | 89 ++++++++++++++++++++++++++++++++++
 include/uapi/drm/drm.h         |  7 +++
 3 files changed, 97 insertions(+)

diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
index 690505a1f7a5..6f78954cae16 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -243,6 +243,7 @@ static inline void drm_debugfs_encoder_remove(struct drm_encoder *encoder)
 drm_ioctl_t drm_version;
 drm_ioctl_t drm_getunique;
 drm_ioctl_t drm_getclient;
+drm_ioctl_t drm_getclients;
 
 /* drm_syncobj.c */
 void drm_syncobj_open(struct drm_file *file_private);
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index e368fc084c77..da7057376581 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -207,6 +207,93 @@ int drm_getclient(struct drm_device *dev, void *data,
 	}
 }
 
+/*
+ * Get list of client PIDs who have opened a DRM file
+ *
+ * \param dev DRM device we are querying
+ * \param data IOCTL command input.
+ * \param file_priv DRM file private.
+ *
+ * \return zero on success or a negative number on failure.
+ *
+ * Traverses list of open clients for the given DRM device, and
+ * copies them into userpace as an array of PIDs
+ */
+int drm_getclients(struct drm_device *dev, void *data,
+		   struct drm_file *file_priv)
+
+{
+	struct drm_get_clients *get_clients = data;
+	ssize_t size = get_clients->len;
+	char __user *pid_buf;
+	ssize_t offset = 0;
+	int ret = 0;
+
+	/*
+	 * We do not want to show clients of display only devices so
+	 * as to avoid confusing UM GPU profilers
+	 */
+	if (!dev->render) {
+		get_clients->len = 0;
+		return 0;
+	}
+
+	/*
+	 * An input size of zero means UM wants to know the size of the PID buffer
+	 * We round it up to the nearest multiple of the page size so that we can have
+	 * some spare headroom in case more clients came in between successive calls
+	 * of this ioctl, and also to simplify parsing of the PIDs buffer, because
+	 * sizeof(pid_t) will hopefully always divide PAGE_SIZE
+	 */
+	if (size == 0) {
+		get_clients->len =
+			roundup(atomic_read(&dev->open_count) * sizeof(pid_t), PAGE_SIZE);
+		return 0;
+	}
+
+	pid_buf = (char *)(void *)get_clients->user_data;
+
+	if (!pid_buf)
+		return -EINVAL;
+
+	mutex_lock(&dev->filelist_mutex);
+	list_for_each_entry_reverse(file_priv, &dev->filelist, lhead) {
+		pid_t pid_num;
+
+		if ((size - offset) < sizeof(pid_t))
+			break;
+
+		rcu_read_lock();
+		pid_num = pid_vnr(rcu_dereference(file_priv->pid));
+		rcu_read_unlock();
+
+		/* We do not want to return the profiler's PID */
+		if (pid_vnr(task_tgid(current)) == pid_num)
+			continue;
+
+		ret = copy_to_user(pid_buf + offset, &pid_num, sizeof(pid_t));
+		if (ret)
+			break;
+
+		offset += sizeof(pid_t);
+	}
+	mutex_unlock(&dev->filelist_mutex);
+
+	if (ret)
+		return -EFAULT;
+
+	if ((size - offset) >= sizeof(pid_t)) {
+		pid_t pid_zero = 0;
+
+		ret = copy_to_user(pid_buf + offset,
+				   &pid_zero, sizeof(pid_t));
+		if (ret)
+			return -EFAULT;
+	}
+
+	return 0;
+}
+
 /*
  * Get statistics information.
  *
@@ -672,6 +759,8 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_LIST_LESSEES, drm_mode_list_lessees_ioctl, DRM_MASTER),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GET_LEASE, drm_mode_get_lease_ioctl, DRM_MASTER),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_REVOKE_LEASE, drm_mode_revoke_lease_ioctl, DRM_MASTER),
+
+	DRM_IOCTL_DEF(DRM_IOCTL_GET_CLIENTS, drm_getclients, DRM_RENDER_ALLOW),
 };
 
 #define DRM_CORE_IOCTL_COUNT	ARRAY_SIZE(drm_ioctls)
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 16122819edfe..c47aa9de51ab 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -1024,6 +1024,11 @@ struct drm_crtc_queue_sequence {
 	__u64 user_data;	/* user data passed to event */
 };
 
+struct drm_get_clients {
+	__u64 user_data;
+	__kernel_size_t len;
+};
+
 #if defined(__cplusplus)
 }
 #endif
@@ -1236,6 +1241,8 @@ extern "C" {
 #define DRM_IOCTL_SYNCOBJ_TRANSFER	DRM_IOWR(0xCC, struct drm_syncobj_transfer)
 #define DRM_IOCTL_SYNCOBJ_TIMELINE_SIGNAL	DRM_IOWR(0xCD, struct drm_syncobj_timeline_array)
 
+#define DRM_IOCTL_GET_CLIENTS		DRM_IOWR(0xD1, struct drm_get_clients)
+
 /**
  * DRM_IOCTL_MODE_GETFB2 - Get framebuffer metadata.
  *
-- 
2.44.0