[PATCH 1/2] driver: xen-blkfront: move talk_to_blkback to the correct place

[Bob Liu <bob.liu@oracle.com>]

The right place for talk_to_blkback() to query backend features and transport
parameters is after backend entered XenbusStateInitWait. There is no problem
with this yet, but it is an violation of the design and furthermore it would not
allow frontend/backend to negotiate 'multi-page' and 'multi-queue' features
which require this.

This patch move talk_to_blkback() to blkback_changed() after backend entered
XenbusStateInitWait just like blkif.h defined:

See: xen/include/public/io/blkif.h
Front                                Back
=================================    =====================================
XenbusStateInitialising              XenbusStateInitialising
 o Query virtual device               o Query backend device identification
   properties.                          data.
 o Setup OS device instance.          o Open and validate backend device.
                                      o Publish backend features and
                                        transport parameters.
                                                     |
                                                     |
                                                     V
                                     XenbusStateInitWait

o Query backend features and
  transport parameters.
o Allocate and initialize the
  request ring.
o Publish transport parameters
  that will be in effect during
  this connection.
             |
             |
             V
XenbusStateInitialised

                                      o Query frontend transport parameters.
                                      o Connect to the request ring and
                                        event channel.
                                      o Publish backend device properties.
                                                     |
                                                     |
                                                     V
                                     XenbusStateConnected

 o Query backend device properties.
 o Finalize OS virtual device
   instance.
             |
             |
             V
XenbusStateConnected

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 drivers/block/xen-blkfront.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2c61cf8..88e23fd 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1430,13 +1430,6 @@ static int blkfront_probe(struct xenbus_device *dev,
 	info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
 	dev_set_drvdata(&dev->dev, info);
 
-	err = talk_to_blkback(dev, info);
-	if (err) {
-		kfree(info);
-		dev_set_drvdata(&dev->dev, NULL);
-		return err;
-	}
-
 	return 0;
 }
 
@@ -1906,8 +1899,13 @@ static void blkback_changed(struct xenbus_device *dev,
 	dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);
 
 	switch (backend_state) {
-	case XenbusStateInitialising:
 	case XenbusStateInitWait:
+		if (talk_to_blkback(dev, info)) {
+			kfree(info);
+			dev_set_drvdata(&dev->dev, NULL);
+			break;
+		}
+	case XenbusStateInitialising:
 	case XenbusStateInitialised:
 	case XenbusStateReconfiguring:
 	case XenbusStateReconfigured:
-- 
1.8.3.1