xen/xenbus: Add 'will_handle' callback support in xenbus_watch_path()

Some code does not directly make 'xenbus_watch' object and call
'register_xenbus_watch()' but use 'xenbus_watch_path()' instead.  This
commit adds support of 'will_handle' callback in the
'xenbus_watch_path()' and it's wrapper, 'xenbus_watch_pathfmt()'.

This is part of XSA-349

Cc: stable@vger.kernel.org
Signed-off-by: SeongJae Park <sjpark@amazon.de>
Reported-by: Michael Kurth <mku@amazon.de>
Reported-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/block/xen-blkback/xenbus.c

@@ -675,7 +675,8 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
 	/* setup back pointer */
 	be->blkif->be = be;
 
-	err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
+	err = xenbus_watch_pathfmt(dev, &be->backend_watch, NULL,
+				   backend_changed,
 				   "%s/%s", dev->nodename, "physical-device");
 	if (err)
 		goto fail;

drivers/net/xen-netback/xenbus.c

@@ -824,7 +824,7 @@ static void connect(struct backend_info *be)
 	xenvif_carrier_on(be->vif);
 
 	unregister_hotplug_status_watch(be);
-	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
+	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch, NULL,
 				   hotplug_status_changed,
 				   "%s/%s", dev->nodename, "hotplug-status");
 	if (!err)

drivers/xen/xen-pciback/xenbus.c

@@ -689,7 +689,7 @@ static int xen_pcibk_xenbus_probe(struct xenbus_device *dev,
 
 	/* watch the backend node for backend configuration information */
 	err = xenbus_watch_path(dev, dev->nodename, &pdev->be_watch,
-				xen_pcibk_be_watch);
+				NULL, xen_pcibk_be_watch);
 	if (err)
 		goto out;
 

drivers/xen/xenbus/xenbus_client.c

@@ -127,19 +127,22 @@ EXPORT_SYMBOL_GPL(xenbus_strstate);
  */
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
+		      bool (*will_handle)(struct xenbus_watch *,
+					  const char *, const char *),
 		      void (*callback)(struct xenbus_watch *,
 				       const char *, const char *))
 {
 	int err;
 
 	watch->node = path;
-	watch->will_handle = NULL;
+	watch->will_handle = will_handle;
 	watch->callback = callback;
 
 	err = register_xenbus_watch(watch);
 
 	if (err) {
 		watch->node = NULL;
+		watch->will_handle = NULL;
 		watch->callback = NULL;
 		xenbus_dev_fatal(dev, err, "adding watch on %s", path);
 	}
@@ -166,6 +169,8 @@ EXPORT_SYMBOL_GPL(xenbus_watch_path);
  */
 int xenbus_watch_pathfmt(struct xenbus_device *dev,
 			 struct xenbus_watch *watch,
+			 bool (*will_handle)(struct xenbus_watch *,
+					const char *, const char *),
 			 void (*callback)(struct xenbus_watch *,
 					  const char *, const char *),
 			 const char *pathfmt, ...)
@@ -182,7 +187,7 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev,
 		xenbus_dev_fatal(dev, -ENOMEM, "allocating path for watch");
 		return -ENOMEM;
 	}
-	err = xenbus_watch_path(dev, path, watch, callback);
+	err = xenbus_watch_path(dev, path, watch, will_handle, callback);
 
 	if (err)
 		kfree(path);

drivers/xen/xenbus/xenbus_probe.c

@@ -136,7 +136,7 @@ static int watch_otherend(struct xenbus_device *dev)
 		container_of(dev->dev.bus, struct xen_bus_type, bus);
 
 	return xenbus_watch_pathfmt(dev, &dev->otherend_watch,
-				    bus->otherend_changed,
+				    NULL, bus->otherend_changed,
 				    "%s/%s", dev->otherend, "state");
 }
 

include/xen/xenbus.h

@@ -204,10 +204,14 @@ void xenbus_probe(struct work_struct *);
 
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
+		      bool (*will_handle)(struct xenbus_watch *,
+					  const char *, const char *),
 		      void (*callback)(struct xenbus_watch *,
 				       const char *, const char *));
-__printf(4, 5)
+__printf(5, 6)
 int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch,
+			 bool (*will_handle)(struct xenbus_watch *,
+					     const char *, const char *),
 			 void (*callback)(struct xenbus_watch *,
 					  const char *, const char *),
 			 const char *pathfmt, ...);