[RFC PATCH 15/60] hyper_dmabuf: reusing previously released hyper_dmabuf_id

[Dongwon Kim]

Now, released hyper_dmabuf_ids are stored in a stack -
(hyper_dmabuf_private.id_queue) for reuse. This is to prevent
overflow of ids for buffers. We also limit maximum number for
the id to 1000 for the stability and optimal performance.

Signed-off-by: Dongwon Kim <dongwon.kim@xxxxxxxxx>
---
 drivers/xen/hyper_dmabuf/Makefile                  |  1 +
 drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.c        |  5 ++
 drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.h        |  6 ++
 drivers/xen/hyper_dmabuf/hyper_dmabuf_id.c         | 76 ++++++++++++++++++++++
 drivers/xen/hyper_dmabuf/hyper_dmabuf_id.h         | 24 +++++++
 drivers/xen/hyper_dmabuf/hyper_dmabuf_imp.c        |  1 +
 drivers/xen/hyper_dmabuf/hyper_dmabuf_ioctl.c      | 15 ++---
 .../xen/hyper_dmabuf/hyper_dmabuf_remote_sync.c    |  3 +
 drivers/xen/hyper_dmabuf/hyper_dmabuf_struct.h     |  9 ---
 9 files changed, 120 insertions(+), 20 deletions(-)
 create mode 100644 drivers/xen/hyper_dmabuf/hyper_dmabuf_id.c
 create mode 100644 drivers/xen/hyper_dmabuf/hyper_dmabuf_id.h

diff --git a/drivers/xen/hyper_dmabuf/Makefile b/drivers/xen/hyper_dmabuf/Makefile
index 3459382..c9b8b7f 100644
--- a/drivers/xen/hyper_dmabuf/Makefile
+++ b/drivers/xen/hyper_dmabuf/Makefile
@@ -7,6 +7,7 @@ ifneq ($(KERNELRELEASE),)
                                  hyper_dmabuf_list.o \
 				 hyper_dmabuf_imp.o \
 				 hyper_dmabuf_msg.o \
+				 hyper_dmabuf_id.o \
 				 hyper_dmabuf_remote_sync.o \
 				 xen/hyper_dmabuf_xen_comm.o \
 				 xen/hyper_dmabuf_xen_comm_list.o
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.c b/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.c
index 5a7cfa5..66d6cb9 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.c
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.c
@@ -5,6 +5,7 @@
 #include "hyper_dmabuf_drv.h"
 #include "hyper_dmabuf_conf.h"
 #include "hyper_dmabuf_list.h"
+#include "hyper_dmabuf_id.h"
 #include "xen/hyper_dmabuf_xen_comm_list.h"
 #include "xen/hyper_dmabuf_xen_comm.h"
 
@@ -67,6 +68,10 @@ static void hyper_dmabuf_drv_exit(void)
 	if (hyper_dmabuf_private.work_queue)
 		destroy_workqueue(hyper_dmabuf_private.work_queue);
 
+	/* destroy id_queue */
+	if (hyper_dmabuf_private.id_queue)
+		destroy_reusable_list();
+
 	hyper_dmabuf_destroy_data_dir();
 	printk( KERN_NOTICE "dma_buf-src_sink model: Exiting" );
 	unregister_device();
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.h b/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.h
index ff883e1..37b0cc1 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.h
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_drv.h
@@ -1,10 +1,16 @@
 #ifndef __LINUX_PUBLIC_HYPER_DMABUF_DRV_H__
 #define __LINUX_PUBLIC_HYPER_DMABUF_DRV_H__
 
+struct list_reusable_id {
+	int id;
+	struct list_head list;
+};
+
 struct hyper_dmabuf_private {
         struct device *device;
 	int domid;
 	struct workqueue_struct *work_queue;
+	struct list_reusable_id *id_queue;
 };
 
 typedef int (*hyper_dmabuf_ioctl_t)(void *data);
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.c b/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.c
new file mode 100644
index 0000000..7bbb179
--- /dev/null
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.c
@@ -0,0 +1,76 @@
+#include <linux/list.h>
+#include <linux/slab.h>
+#include "hyper_dmabuf_drv.h"
+#include "hyper_dmabuf_id.h"
+
+extern struct hyper_dmabuf_private hyper_dmabuf_private;
+
+void store_reusable_id(int id)
+{
+	struct list_reusable_id *reusable_head = hyper_dmabuf_private.id_queue;
+	struct list_reusable_id *new_reusable;
+
+	new_reusable = kmalloc(sizeof(*new_reusable), GFP_KERNEL);
+	new_reusable->id = id;
+
+	list_add(&new_reusable->list, &reusable_head->list);
+}
+
+static int retrieve_reusable_id(void)
+{
+	struct list_reusable_id *reusable_head = hyper_dmabuf_private.id_queue;
+
+	/* check there is reusable id */
+	if (!list_empty(&reusable_head->list)) {
+		reusable_head = list_first_entry(&reusable_head->list,
+						 struct list_reusable_id,
+						 list);
+
+		list_del(&reusable_head->list);
+		return reusable_head->id;
+	}
+
+	return -1;
+}
+
+void destroy_reusable_list(void)
+{
+	struct list_reusable_id *reusable_head = hyper_dmabuf_private.id_queue;
+	struct list_reusable_id *temp_head;
+
+	if (reusable_head) {
+		/* freeing mem space all reusable ids in the stack */
+		while (!list_empty(&reusable_head->list)) {
+			temp_head = list_first_entry(&reusable_head->list,
+						     struct list_reusable_id,
+						     list);
+			list_del(&temp_head->list);
+			kfree(temp_head);
+		}
+
+		/* freeing head */
+		kfree(reusable_head);
+	}
+}
+
+int hyper_dmabuf_get_id(void)
+{
+	static int id = 0;
+	struct list_reusable_id *reusable_head;
+	int ret;
+
+	/* first cla to hyper_dmabuf_get_id */
+	if (id == 0) {
+		reusable_head = kmalloc(sizeof(*reusable_head), GFP_KERNEL);
+		reusable_head->id = -1; /* list head have invalid id */
+		INIT_LIST_HEAD(&reusable_head->list);
+		hyper_dmabuf_private.id_queue = reusable_head;
+	}
+
+	ret = retrieve_reusable_id();
+
+	if (ret < 0 && id < HYPER_DMABUF_ID_MAX)
+		return HYPER_DMABUF_ID_CREATE(hyper_dmabuf_private.domid, id++);
+
+	return ret;
+}
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.h b/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.h
new file mode 100644
index 0000000..2c8daf3
--- /dev/null
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_id.h
@@ -0,0 +1,24 @@
+#ifndef __HYPER_DMABUF_ID_H__
+#define __HYPER_DMABUF_ID_H__
+
+/* Importer combine source domain id with given hyper_dmabuf_id
+ * to make it unique in case there are multiple exporters */
+
+#define HYPER_DMABUF_ID_CREATE(domid, id) \
+	((((domid) & 0xFF) << 24) | ((id) & 0xFFFFFF))
+
+#define HYPER_DMABUF_DOM_ID(id) \
+	(((id) >> 24) & 0xFF)
+
+/* currently maximum number of buffers shared
+ * at any given moment is limited to 1000
+ */
+#define HYPER_DMABUF_ID_MAX 1000
+
+void store_reusable_id(int id);
+
+void destroy_reusable_list(void);
+
+int hyper_dmabuf_get_id(void);
+
+#endif /*__HYPER_DMABUF_ID_H*/
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_imp.c b/drivers/xen/hyper_dmabuf/hyper_dmabuf_imp.c
index fa445e5..b109138 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_imp.c
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_imp.c
@@ -7,6 +7,7 @@
 #include <asm/xen/page.h>
 #include "hyper_dmabuf_struct.h"
 #include "hyper_dmabuf_imp.h"
+#include "hyper_dmabuf_id.h"
 #include "xen/hyper_dmabuf_xen_comm.h"
 #include "hyper_dmabuf_msg.h"
 #include "hyper_dmabuf_list.h"
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_ioctl.c b/drivers/xen/hyper_dmabuf/hyper_dmabuf_ioctl.c
index e334b77..5c6d9c8 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_ioctl.c
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_ioctl.c
@@ -11,6 +11,7 @@
 #include "hyper_dmabuf_imp.h"
 #include "hyper_dmabuf_list.h"
 #include "hyper_dmabuf_drv.h"
+#include "hyper_dmabuf_id.h"
 #include "hyper_dmabuf_query.h"
 #include "xen/hyper_dmabuf_xen_comm.h"
 #include "xen/hyper_dmabuf_xen_comm_list.h"
@@ -18,16 +19,6 @@
 
 extern struct hyper_dmabuf_private hyper_dmabuf_private;
 
-static uint32_t hyper_dmabuf_id_gen(void) {
-	/* TODO: add proper implementation */
-	static uint32_t id = 1000;
-	static int32_t domid = -1;
-	if (domid == -1) {
-		domid = hyper_dmabuf_get_domid();
-	}
-	return HYPER_DMABUF_ID_IMPORTER(domid, id++);
-}
-
 static int hyper_dmabuf_exporter_ring_setup(void *data)
 {
 	struct ioctl_hyper_dmabuf_exporter_ring_setup *ring_attr;
@@ -133,7 +124,7 @@ static int hyper_dmabuf_export_remote(void *data)
 
 	sgt_info = kmalloc(sizeof(*sgt_info), GFP_KERNEL);
 
-	sgt_info->hyper_dmabuf_id = hyper_dmabuf_id_gen();
+	sgt_info->hyper_dmabuf_id = hyper_dmabuf_get_id();
 	/* TODO: We might need to consider using port number on event channel? */
 	sgt_info->hyper_dmabuf_rdomain = export_remote_attr->remote_domain;
 	sgt_info->dma_buf = dma_buf;
@@ -334,6 +325,8 @@ static int hyper_dmabuf_unexport(void *data)
 		hyper_dmabuf_cleanup_sgt_info(sgt_info, false);
 		hyper_dmabuf_remove_exported(unexport_attr->hyper_dmabuf_id);
 		kfree(sgt_info);
+		/* register hyper_dmabuf_id to the list for reuse */
+		store_reusable_id(unexport_attr->hyper_dmabuf_id);
 	}
 
 	return ret;
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_remote_sync.c b/drivers/xen/hyper_dmabuf/hyper_dmabuf_remote_sync.c
index 5017b17..c5950e0 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_remote_sync.c
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_remote_sync.c
@@ -6,6 +6,7 @@
 #include "hyper_dmabuf_struct.h"
 #include "hyper_dmabuf_list.h"
 #include "hyper_dmabuf_drv.h"
+#include "hyper_dmabuf_id.h"
 #include "xen/hyper_dmabuf_xen_comm.h"
 #include "hyper_dmabuf_msg.h"
 #include "hyper_dmabuf_imp.h"
@@ -124,6 +125,8 @@ int hyper_dmabuf_remote_sync(int id, int ops)
 			hyper_dmabuf_cleanup_sgt_info(sgt_info, false);
 			hyper_dmabuf_remove_exported(id);
 			kfree(sgt_info);
+			/* store hyper_dmabuf_id in the list for reuse */
+			store_reusable_id(id);
 		}
 
 		break;
diff --git a/drivers/xen/hyper_dmabuf/hyper_dmabuf_struct.h b/drivers/xen/hyper_dmabuf/hyper_dmabuf_struct.h
index 92e06ff..b52f958 100644
--- a/drivers/xen/hyper_dmabuf/hyper_dmabuf_struct.h
+++ b/drivers/xen/hyper_dmabuf/hyper_dmabuf_struct.h
@@ -3,15 +3,6 @@
 
 #include <xen/interface/grant_table.h>
 
-/* Importer combine source domain id with given hyper_dmabuf_id
- * to make it unique in case there are multiple exporters */
-
-#define HYPER_DMABUF_ID_IMPORTER(domid, id) \
-	((((domid) & 0xFF) << 24) | ((id) & 0xFFFFFF))
-
-#define HYPER_DMABUF_DOM_ID(id) \
-	(((id) >> 24) & 0xFF)
-
 /* each grant_ref_t is 4 bytes, so total 4096 grant_ref_t can be
  * in this block meaning we can share 4KB*4096 = 16MB of buffer
  * (needs to be increased for large buffer use-cases such as 4K
-- 
2.7.4