dma-buf: Do not build debugfs related code when !CONFIG_DEBUG_FS

There is no point in compiling in the list and mutex operations which are
only used from the dma-buf debugfs code, if debugfs is not compiled in.

Put the code in questions behind some kconfig guards and so save some text
and maybe even a pointer per object at runtime when not enabled.

Signed-off-by: Tvrtko Ursulin <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Reviewed-by: T.J. Mercier <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Maíra Canal <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/dma-buf.c

···
 
 static inline int is_dma_buf_file(struct file *);
 
-struct dma_buf_list {
-	struct list_head head;
-	struct mutex lock;
-};
+#if IS_ENABLED(CONFIG_DEBUG_FS)
+static DEFINE_MUTEX(debugfs_list_mutex);
+static LIST_HEAD(debugfs_list);
 
-static struct dma_buf_list db_list;
+static void __dma_buf_debugfs_list_add(struct dma_buf *dmabuf)
+{
+	mutex_lock(&debugfs_list_mutex);
+	list_add(&dmabuf->list_node, &debugfs_list);
+	mutex_unlock(&debugfs_list_mutex);
+}
+
+static void __dma_buf_debugfs_list_del(struct dma_buf *dmabuf)
+{
+	if (!dmabuf)
+		return;
+
+	mutex_lock(&debugfs_list_mutex);
+	list_del(&dmabuf->list_node);
+	mutex_unlock(&debugfs_list_mutex);
+}
+#else
+static void __dma_buf_debugfs_list_add(struct dma_buf *dmabuf)
+{
+}
+
+static void __dma_buf_debugfs_list_del(struct file *file)
+{
+}
+#endif
 
 static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
 {
···
 
 static int dma_buf_file_release(struct inode *inode, struct file *file)
 {
-	struct dma_buf *dmabuf;
-
 	if (!is_dma_buf_file(file))
 		return -EINVAL;
 
-	dmabuf = file->private_data;
-	if (dmabuf) {
-		mutex_lock(&db_list.lock);
-		list_del(&dmabuf->list_node);
-		mutex_unlock(&db_list.lock);
-	}
+	__dma_buf_debugfs_list_del(file->private_data);
 
 	return 0;
 }
···
 	file->f_path.dentry->d_fsdata = dmabuf;
 	dmabuf->file = file;
 
-	mutex_lock(&db_list.lock);
-	list_add(&dmabuf->list_node, &db_list.head);
-	mutex_unlock(&db_list.lock);
+	__dma_buf_debugfs_list_add(dmabuf);
 
 	return dmabuf;
 
···
 	size_t size = 0;
 	int ret;
 
-	ret = mutex_lock_interruptible(&db_list.lock);
+	ret = mutex_lock_interruptible(&debugfs_list_mutex);
 
 	if (ret)
 		return ret;
···
 	seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\t%-8s\tname\n",
 		   "size", "flags", "mode", "count", "ino");
 
-	list_for_each_entry(buf_obj, &db_list.head, list_node) {
+	list_for_each_entry(buf_obj, &debugfs_list, list_node) {
 
 		ret = dma_resv_lock_interruptible(buf_obj->resv, NULL);
 		if (ret)
···
 
 	seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);
 
-	mutex_unlock(&db_list.lock);
+	mutex_unlock(&debugfs_list_mutex);
 	return 0;
 
 error_unlock:
-	mutex_unlock(&db_list.lock);
+	mutex_unlock(&debugfs_list_mutex);
 	return ret;
 }
 
···
 	if (IS_ERR(dma_buf_mnt))
 		return PTR_ERR(dma_buf_mnt);
 
-	mutex_init(&db_list.lock);
-	INIT_LIST_HEAD(&db_list.head);
 	dma_buf_init_debugfs();
 	return 0;
 }

include/linux/dma-buf.h

···
 	 */
 	struct module *owner;
 
+#if IS_ENABLED(CONFIG_DEBUG_FS)
 	/** @list_node: node for dma_buf accounting and debugging. */
 	struct list_head list_node;
+#endif
 
 	/** @priv: exporter specific private data for this buffer object. */
 	void *priv;