From 9acebec0b9b707bd8f525d3eb668f97d0d925094 Mon Sep 17 00:00:00 2001
From: "cl349@firebug.cl.cam.ac.uk" <cl349@firebug.cl.cam.ac.uk>
Date: Wed, 24 Aug 2005 20:11:07 +0000
Subject: [PATCH] Avoid calling device_unregister from device_register
 callback. Also simplify code. Signed-off-by: Christian Limpach
 <Christian.Limpach@cl.cam.ac.uk>

---
 .../drivers/xen/blkback/xenbus.c              | 102 ++++++++----------
 1 file changed, 46 insertions(+), 56 deletions(-)

diff --git a/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c b/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c
index 2f2fdfc3cd..2a445a3983 100644
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/xenbus.c
@@ -64,7 +64,7 @@ static void frontend_changed(struct xenbus_watch *watch, const char *node)
 		= container_of(watch, struct backend_info, watch);
 
 	/* If other end is gone, delete ourself. */
-	if (!xenbus_exists(be->frontpath, "")) {
+	if (node && !xenbus_exists(be->frontpath, "")) {
 		xenbus_rm(be->dev->nodename, "");
 		device_unregister(&be->dev->dev);
 		return;
@@ -139,62 +139,22 @@ static void backend_changed(struct xenbus_watch *watch, const char *node)
 {
 	int err;
 	char *p;
-	char *frontend;
 	long int handle, pdev;
 	struct backend_info *be
 		= container_of(watch, struct backend_info, backend_watch);
 	struct xenbus_device *dev = be->dev;
 
-	frontend = NULL;
-	err = xenbus_gather(dev->nodename,
-			    "frontend-id", "%li", &be->frontend_id,
-			    "frontend", NULL, &frontend,
-			    NULL);
-	if (XENBUS_EXIST_ERR(err) ||
-	    strlen(frontend) == 0 || !xenbus_exists(frontend, "")) {
-		/* If we can't get a frontend path and a frontend-id,
-		 * then our bus-id is no longer valid and we need to
-		 * destroy the backend device.
-		 */
-		goto device_fail;
-	}
-	if (err < 0) {
-		xenbus_dev_error(dev, err,
-				 "reading %s/frontend or frontend-id",
-				 dev->nodename);
-		goto device_fail;
-	}
-
-	if (!be->frontpath || strcmp(frontend, be->frontpath)) {
-		if (be->watch.node)
-			unregister_xenbus_watch(&be->watch);
-		if (be->frontpath)
-			kfree(be->frontpath);
-		be->frontpath = frontend;
-		frontend = NULL;
-		be->watch.node = be->frontpath;
-		be->watch.callback = frontend_changed;
-		err = register_xenbus_watch(&be->watch);
-		if (err) {
-			be->watch.node = NULL;
-			xenbus_dev_error(dev, err,
-					 "adding frontend watch on %s",
-					 be->frontpath);
-			goto device_fail;
-		}
-	}
-
 	err = xenbus_scanf(dev->nodename, "physical-device", "%li", &pdev);
 	if (XENBUS_EXIST_ERR(err))
-		goto out;
+		return;
 	if (err < 0) {
 		xenbus_dev_error(dev, err, "reading physical-device");
-		goto device_fail;
+		return;
 	}
 	if (be->pdev && be->pdev != pdev) {
 		printk(KERN_WARNING
 		       "changing physical-device not supported\n");
-		goto device_fail;
+		return;
 	}
 	be->pdev = pdev;
 
@@ -215,32 +175,25 @@ static void backend_changed(struct xenbus_watch *watch, const char *node)
 			err = PTR_ERR(be->blkif);
 			be->blkif = NULL;
 			xenbus_dev_error(dev, err, "creating block interface");
-			goto device_fail;
+			return;
 		}
 
 		err = vbd_create(be->blkif, handle, be->pdev, be->readonly);
 		if (err) {
 			xenbus_dev_error(dev, err, "creating vbd structure");
-			goto device_fail;
+			return;
 		}
 
-		frontend_changed(&be->watch, be->frontpath);
+		/* Pass in NULL node to skip exist test. */
+		frontend_changed(&be->watch, NULL);
 	}
-
- out:
-	if (frontend)
-		kfree(frontend);
-	return;
-
- device_fail:
-	device_unregister(&be->dev->dev);
-	goto out;
 }
 
 static int blkback_probe(struct xenbus_device *dev,
 			 const struct xenbus_device_id *id)
 {
 	struct backend_info *be;
+	char *frontend;
 	int err;
 
 	be = kmalloc(sizeof(*be), GFP_KERNEL);
@@ -263,9 +216,46 @@ static int blkback_probe(struct xenbus_device *dev,
 
 	dev->data = be;
 
+	frontend = NULL;
+	err = xenbus_gather(dev->nodename,
+			    "frontend-id", "%li", &be->frontend_id,
+			    "frontend", NULL, &frontend,
+			    NULL);
+	if (XENBUS_EXIST_ERR(err))
+		goto free_be;
+	if (frontend &&
+	    (strlen(frontend) == 0 || !xenbus_exists(frontend, ""))) {
+		/* If we can't get a frontend path and a frontend-id,
+		 * then our bus-id is no longer valid and we need to
+		 * destroy the backend device.
+		 */
+		goto free_be;
+	}
+	if (err < 0) {
+		xenbus_dev_error(dev, err,
+				 "reading %s/frontend or frontend-id",
+				 dev->nodename);
+		goto free_be;
+	}
+
+	be->frontpath = frontend;
+	be->watch.node = be->frontpath;
+	be->watch.callback = frontend_changed;
+	err = register_xenbus_watch(&be->watch);
+	if (err) {
+		be->watch.node = NULL;
+		xenbus_dev_error(dev, err,
+				 "adding frontend watch on %s",
+				 be->frontpath);
+		goto free_be;
+	}
+
 	backend_changed(&be->backend_watch, dev->nodename);
 	return err;
+
  free_be:
+	if (frontend)
+		kfree(frontend);
 	kfree(be);
 	return err;
 }
-- 
2.30.2