improve bsg device allocation

This patch addresses on two issues on bsg device allocation.

- the current maxium number of bsg devices is 256. It's too small if
we allocate bsg devices to all SCSI devices, transport entities, etc.
This increses the maxium number to 32768 (taken from the sg driver).

- SCSI devices are dynamically added and removed. Currently, bsg can't
handle it well since bsd_device->minor is simply increased.

This is dependent on the patchset that I posted yesterday:

http://marc.info/?l=linux-scsi&m=117440208726755&w=2

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/bsg.c

@@ -58,6 +58,7 @@ enum {
 };
 
 #define BSG_DEFAULT_CMDS	64
+#define BSG_MAX_DEVS		32768
 
 #undef BSG_DEBUG
 
@@ -75,7 +76,7 @@ enum {
 #define BSG_MAJOR	(240)
 
 static DEFINE_MUTEX(bsg_mutex);
-static int bsg_device_nr;
+static int bsg_device_nr, bsg_minor_idx;
 
 #define BSG_LIST_SIZE	(8)
 #define bsg_list_idx(minor)	((minor) & (BSG_LIST_SIZE - 1))
@@ -957,14 +958,15 @@ void bsg_unregister_queue(struct request_queue *q)
 	class_device_destroy(bsg_class, MKDEV(BSG_MAJOR, bcd->minor));
 	bcd->class_dev = NULL;
 	list_del_init(&bcd->list);
+	bsg_device_nr--;
 	mutex_unlock(&bsg_mutex);
 }
 
 int bsg_register_queue(struct request_queue *q, char *name)
 {
-	struct bsg_class_device *bcd;
+	struct bsg_class_device *bcd, *__bcd;
 	dev_t dev;
-	int ret;
+	int ret = -EMFILE;
 	struct class_device *class_dev = NULL;
 
 	/*
@@ -978,10 +980,27 @@ int bsg_register_queue(struct request_queue *q, char *name)
 	INIT_LIST_HEAD(&bcd->list);
 
 	mutex_lock(&bsg_mutex);
-	dev = MKDEV(BSG_MAJOR, bsg_device_nr);
-	bcd->minor = bsg_device_nr;
-	bsg_device_nr++;
+	if (bsg_device_nr == BSG_MAX_DEVS) {
+		printk(KERN_ERR "bsg: too many bsg devices\n");
+		goto err;
+	}
+
+retry:
+	list_for_each_entry(__bcd, &bsg_class_list, list) {
+		if (__bcd->minor == bsg_minor_idx) {
+			bsg_minor_idx++;
+			if (bsg_minor_idx == BSG_MAX_DEVS)
+				bsg_minor_idx = 0;
+			goto retry;
+		}
+	}
+
+	bcd->minor = bsg_minor_idx++;
+	if (bsg_minor_idx == BSG_MAX_DEVS)
+		bsg_minor_idx = 0;
+
 	bcd->queue = q;
+	dev = MKDEV(BSG_MAJOR, bcd->minor);
 	class_dev = class_device_create(bsg_class, NULL, dev, bcd->dev, "%s", name);
 	if (IS_ERR(class_dev)) {
 		ret = PTR_ERR(class_dev);
@@ -996,11 +1015,11 @@ int bsg_register_queue(struct request_queue *q, char *name)
 	}
 
 	list_add_tail(&bcd->list, &bsg_class_list);
+	bsg_device_nr++;
 
 	mutex_unlock(&bsg_mutex);
 	return 0;
 err:
-	bsg_device_nr--;
 	if (class_dev)
 		class_device_destroy(bsg_class, MKDEV(BSG_MAJOR, bcd->minor));
 	mutex_unlock(&bsg_mutex);
@@ -1030,6 +1049,11 @@ static struct class_interface bsg_intf = {
 	.remove	= bsg_remove,
 };
 
+static struct cdev bsg_cdev = {
+	.kobj   = {.name = "bsg", },
+	.owner  = THIS_MODULE,
+};
+
 static int __init bsg_init(void)
 {
 	int ret, i;
@@ -1050,10 +1074,19 @@ static int __init bsg_init(void)
 		return PTR_ERR(bsg_class);
 	}
 
-	ret = register_chrdev(BSG_MAJOR, "bsg", &bsg_fops);
+	ret = register_chrdev_region(MKDEV(BSG_MAJOR, 0), BSG_MAX_DEVS, "bsg");
+	if (ret) {
+		kmem_cache_destroy(bsg_cmd_cachep);
+		class_destroy(bsg_class);
+		return ret;
+	}
+
+	cdev_init(&bsg_cdev, &bsg_fops);
+	ret = cdev_add(&bsg_cdev, MKDEV(BSG_MAJOR, 0), BSG_MAX_DEVS);
 	if (ret) {
 		kmem_cache_destroy(bsg_cmd_cachep);
 		class_destroy(bsg_class);
+		unregister_chrdev_region(MKDEV(BSG_MAJOR, 0), BSG_MAX_DEVS);
 		return ret;
 	}