[SCSI] bsg: add release callback support

This patch adds release callback support, which is called when a bsg
device goes away. bsg_register_queue() takes a pointer to a callback
function. This feature is useful for stuff like sas_host that can't
use the release callback in struct device.

If a caller doesn't need bsg's release callback, it can call
bsg_register_queue() with NULL pointer (e.g. scsi devices can use
release callback in struct device so they don't need bsg's callback).

With this patch, bsg uses kref for refcounts on bsg devices instead of
get/put_device in fops->open/release. bsg calls put_device and the
caller's release callback (if it was registered) in kref_put's
release.

Signed-off-by: FUJITA Tomonori <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

block/bsg.c

···
 	return bd;
 }
 
+static void bsg_kref_release_function(struct kref *kref)
+{
+	struct bsg_class_device *bcd =
+		container_of(kref, struct bsg_class_device, ref);
+
+	if (bcd->release)
+		bcd->release(bcd->parent);
+
+	put_device(bcd->parent);
+}
+
 static int bsg_put_device(struct bsg_device *bd)
 {
-	int ret = 0;
-	struct device *dev = bd->queue->bsg_dev.dev;
+	int ret = 0, do_free;
+	struct request_queue *q = bd->queue;
 
 	mutex_lock(&bsg_mutex);
 
-	if (!atomic_dec_and_test(&bd->ref_count))
+	do_free = atomic_dec_and_test(&bd->ref_count);
+	if (!do_free)
 		goto out;
 
 	dprintk("%s: tearing down\n", bd->name);
···
 	 */
 	ret = bsg_complete_all_commands(bd);
 
-	blk_put_queue(bd->queue);
 	hlist_del(&bd->dev_list);
 	kfree(bd);
 out:
 	mutex_unlock(&bsg_mutex);
-	put_device(dev);
+	kref_put(&q->bsg_dev.ref, bsg_kref_release_function);
+	if (do_free)
+		blk_put_queue(q);
 	return ret;
 }
 
···
 	mutex_lock(&bsg_mutex);
 	bcd = idr_find(&bsg_minor_idr, iminor(inode));
 	if (bcd)
-		get_device(bcd->dev);
+		kref_get(&bcd->ref);
 	mutex_unlock(&bsg_mutex);
 
 	if (!bcd)
···
 
 	bd = bsg_add_device(inode, bcd->queue, file);
 	if (IS_ERR(bd))
-		put_device(bcd->dev);
+		kref_put(&bcd->ref, bsg_kref_release_function);
 
 	return bd;
 }
···
 	idr_remove(&bsg_minor_idr, bcd->minor);
 	sysfs_remove_link(&q->kobj, "bsg");
 	device_unregister(bcd->class_dev);
-	put_device(bcd->dev);
 	bcd->class_dev = NULL;
+	kref_put(&bcd->ref, bsg_kref_release_function);
 	mutex_unlock(&bsg_mutex);
 }
 EXPORT_SYMBOL_GPL(bsg_unregister_queue);
 
-int bsg_register_queue(struct request_queue *q, struct device *gdev,
-		       const char *name)
+int bsg_register_queue(struct request_queue *q, struct device *parent,
+		       const char *name, void (*release)(struct device *))
 {
 	struct bsg_class_device *bcd;
 	dev_t dev;
···
 	if (name)
 		devname = name;
 	else
-		devname = gdev->bus_id;
+		devname = parent->bus_id;
 
 	/*
 	 * we need a proper transport to send commands, not a stacked device
···
 
 	bcd->minor = minor;
 	bcd->queue = q;
-	bcd->dev = get_device(gdev);
+	bcd->parent = get_device(parent);
+	bcd->release = release;
+	kref_init(&bcd->ref);
 	dev = MKDEV(bsg_major, bcd->minor);
-	class_dev = device_create(bsg_class, gdev, dev, "%s", devname);
+	class_dev = device_create(bsg_class, parent, dev, "%s", devname);
 	if (IS_ERR(class_dev)) {
 		ret = PTR_ERR(class_dev);
 		goto put_dev;
···
 unregister_class_dev:
 	device_unregister(class_dev);
 put_dev:
-	put_device(gdev);
+	put_device(parent);
 remove_idr:
 	idr_remove(&bsg_minor_idr, minor);
 unlock:

drivers/scsi/scsi_sysfs.c

···
 		goto out;
 	}
 
-	error = bsg_register_queue(rq, &sdev->sdev_gendev, NULL);
+	error = bsg_register_queue(rq, &sdev->sdev_gendev, NULL, NULL);
 
 	if (error)
 		sdev_printk(KERN_INFO, sdev,

drivers/scsi/scsi_transport_sas.c

···
 	if (!q)
 		return -ENOMEM;
 
-	error = bsg_register_queue(q, dev, name);
+	error = bsg_register_queue(q, dev, name, NULL);
 	if (error) {
 		blk_cleanup_queue(q);
 		return -ENOMEM;

include/linux/bsg.h

···
 #if defined(CONFIG_BLK_DEV_BSG)
 struct bsg_class_device {
 	struct device *class_dev;
-	struct device *dev;
+	struct device *parent;
 	int minor;
 	struct request_queue *queue;
+	struct kref ref;
+	void (*release)(struct device *);
 };
 
-extern int bsg_register_queue(struct request_queue *, struct device *, const char *);
+extern int bsg_register_queue(struct request_queue *q,
+			      struct device *parent, const char *name,
+			      void (*release)(struct device *));
 extern void bsg_unregister_queue(struct request_queue *);
 #else
-static inline int bsg_register_queue(struct request_queue * rq, struct device *dev, const char *name)
+static inline int bsg_register_queue(struct request_queue *q,
+				     struct device *parent, const char *name,
+				     void (*release)(struct device *))
 {
 	return 0;
 }
-static inline void bsg_unregister_queue(struct request_queue *rq)
+static inline void bsg_unregister_queue(struct request_queue *q)
 {
 }
 #endif