block/rnbd-srv: Replace sess_dev_list with index_idr

The structure rnbd_srv_session maintains a list and an xarray of
rnbd_srv_dev. There is no need to keep both as one of them can serve the
purpose.

Since one of the places where the lookup of rnbd_srv_dev using
rnbd_srv_session is IO path, an xarray would serve us better than a list
traversal. Hence remove sess_dev_list from rnbd_srv_session, and replace
its uses from xarray.
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Reviewed-by: Aleksei Marov <aleksei.marov@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20220707143122.460362-3-haris.iqbal@ionos.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-srv.c

@@ -224,7 +224,6 @@ void rnbd_destroy_sess_dev(struct rnbd_srv_sess_dev *sess_dev, bool keep_id)
 	wait_for_completion(&dc); /* wait for inflights to drop to zero */
 
 	rnbd_dev_close(sess_dev->rnbd_dev);
-	list_del(&sess_dev->sess_list);
 	mutex_lock(&sess_dev->dev->lock);
 	list_del(&sess_dev->dev_list);
 	if (sess_dev->open_flags & FMODE_WRITE)
@@ -239,14 +238,14 @@ void rnbd_destroy_sess_dev(struct rnbd_srv_sess_dev *sess_dev, bool keep_id)
 
 static void destroy_sess(struct rnbd_srv_session *srv_sess)
 {
-	struct rnbd_srv_sess_dev *sess_dev, *tmp;
+	struct rnbd_srv_sess_dev *sess_dev;
+	unsigned long index;
 
-	if (list_empty(&srv_sess->sess_dev_list))
+	if (xa_empty(&srv_sess->index_idr))
 		goto out;
 
 	mutex_lock(&srv_sess->lock);
-	list_for_each_entry_safe(sess_dev, tmp, &srv_sess->sess_dev_list,
-				 sess_list)
+	xa_for_each(&srv_sess->index_idr, index, sess_dev)
 		rnbd_srv_destroy_dev_session_sysfs(sess_dev);
 	mutex_unlock(&srv_sess->lock);
 
@@ -281,7 +280,6 @@ static int create_sess(struct rtrs_srv_sess *rtrs)
 
 	srv_sess->queue_depth = rtrs_srv_get_queue_depth(rtrs);
 	xa_init_flags(&srv_sess->index_idr, XA_FLAGS_ALLOC);
-	INIT_LIST_HEAD(&srv_sess->sess_dev_list);
 	mutex_init(&srv_sess->lock);
 	mutex_lock(&sess_lock);
 	list_add(&srv_sess->list, &sess_list);
@@ -667,11 +665,12 @@ static struct rnbd_srv_sess_dev *
 find_srv_sess_dev(struct rnbd_srv_session *srv_sess, const char *dev_name)
 {
 	struct rnbd_srv_sess_dev *sess_dev;
+	unsigned long index;
 
-	if (list_empty(&srv_sess->sess_dev_list))
+	if (xa_empty(&srv_sess->index_idr))
 		return NULL;
 
-	list_for_each_entry(sess_dev, &srv_sess->sess_dev_list, sess_list)
+	xa_for_each(&srv_sess->index_idr, index, sess_dev)
 		if (!strcmp(sess_dev->pathname, dev_name))
 			return sess_dev;
 
@@ -781,8 +780,6 @@ static int process_msg_open(struct rnbd_srv_session *srv_sess,
 	list_add(&srv_sess_dev->dev_list, &srv_dev->sess_dev_list);
 	mutex_unlock(&srv_dev->lock);
 
-	list_add(&srv_sess_dev->sess_list, &srv_sess->sess_dev_list);
-
 	rnbd_srv_info(srv_sess_dev, "Opened device '%s'\n", srv_dev->id);
 
 	kfree(full_path);

drivers/block/rnbd/rnbd-srv.h

@@ -25,8 +25,6 @@ struct rnbd_srv_session {
 	int			queue_depth;
 
 	struct xarray		index_idr;
-	/* List of struct rnbd_srv_sess_dev */
-	struct list_head        sess_dev_list;
 	struct mutex		lock;
 	u8			ver;
 };
@@ -48,8 +46,6 @@ struct rnbd_srv_dev {
 struct rnbd_srv_sess_dev {
 	/* Entry inside rnbd_srv_dev struct */
 	struct list_head		dev_list;
-	/* Entry inside rnbd_srv_session struct */
-	struct list_head		sess_list;
 	struct rnbd_dev			*rnbd_dev;
 	struct rnbd_srv_session		*sess;
 	struct rnbd_srv_dev		*dev;