linux-kernel - [PATCH v2 1/2] driver: xen-blkfront: move talk_to

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Message-Id: <1432127422-6797-1-git-send-email-bob.liu@oracle.com>
Date:	Wed, 20 May 2015 21:10:21 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	xen-devel@...ts.xen.org
Cc:	david.vrabel@...rix.com, justing@...ctralogic.com,
	konrad.wilk@...cle.com, roger.pau@...rix.com,
	paul.durrant@...rix.com, linux-kernel@...r.kernel.org,
	Bob Liu <bob.liu@...cle.com>
Subject: [PATCH v2 1/2] driver: xen-blkfront: move talk_to_blkback to a more suitable place

The major responsibility of talk_to_blkback() is allocate and initialize the
request ring and writes the ring info stuff out.
But this work should be done after backend entered 'XenbusStateInitWait' as
defined in the protocol file.
See xen/include/public/io/blkif.h in XEN git tree:
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.

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.

Changes in v2:
 - Re-write the commit message to be more clear.

Signed-off-by: Bob Liu <bob.liu@...cle.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

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