linux-kernel - [PATCH 02/12] xen: make use of xenbus_read

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Date:   Mon, 31 Oct 2016 17:48:20 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org
Cc:     david.vrabel@...rix.com, boris.ostrovsky@...cle.com,
        Juergen Gross <jgross@...e.com>, konrad.wilk@...cle.com,
        roger.pau@...rix.com
Subject: [PATCH 02/12] xen: make use of xenbus_read_unsigned() in xen-blkback

Use xenbus_read_unsigned() instead of xenbus_scanf() when possible.
This requires to change the type of one read from int to unsigned,
but this case has been wrong before: negative values are not allowed
for the modified case.

Cc: konrad.wilk@...cle.com
Cc: roger.pau@...rix.com

Signed-off-by: Juergen Gross <jgross@...e.com>
---
 drivers/block/xen-blkback/xenbus.c | 36 ++++++++++++++----------------------
 1 file changed, 14 insertions(+), 22 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 3cc6d1d..415e79b 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -533,13 +533,11 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info
 	struct xenbus_device *dev = be->dev;
 	struct xen_blkif *blkif = be->blkif;
 	int err;
-	int state = 0, discard_enable;
+	int state = 0;
 	struct block_device *bdev = be->blkif->vbd.bdev;
 	struct request_queue *q = bdev_get_queue(bdev);
 
-	err = xenbus_scanf(XBT_NIL, dev->nodename, "discard-enable", "%d",
-			   &discard_enable);
-	if (err == 1 && !discard_enable)
+	if (!xenbus_read_unsigned(dev->nodename, "discard-enable", 1))
 		return;
 
 	if (blk_queue_discard(q)) {
@@ -1039,30 +1037,24 @@ static int connect_ring(struct backend_info *be)
 		xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
 		return -ENOSYS;
 	}
-	err = xenbus_scanf(XBT_NIL, dev->otherend,
-			   "feature-persistent", "%u", &pers_grants);
-	if (err <= 0)
-		pers_grants = 0;
-
+	pers_grants = xenbus_read_unsigned(dev->otherend, "feature-persistent",
+					   0);
 	be->blkif->vbd.feature_gnt_persistent = pers_grants;
 	be->blkif->vbd.overflow_max_grants = 0;
 
 	/*
 	 * Read the number of hardware queues from frontend.
 	 */
-	err = xenbus_scanf(XBT_NIL, dev->otherend, "multi-queue-num-queues",
-			   "%u", &requested_num_queues);
-	if (err < 0) {
-		requested_num_queues = 1;
-	} else {
-		if (requested_num_queues > xenblk_max_queues
-		    || requested_num_queues == 0) {
-			/* Buggy or malicious guest. */
-			xenbus_dev_fatal(dev, err,
-					"guest requested %u queues, exceeding the maximum of %u.",
-					requested_num_queues, xenblk_max_queues);
-			return -ENOSYS;
-		}
+	requested_num_queues = xenbus_read_unsigned(dev->otherend,
+						    "multi-queue-num-queues",
+						    1);
+	if (requested_num_queues > xenblk_max_queues
+	    || requested_num_queues == 0) {
+		/* Buggy or malicious guest. */
+		xenbus_dev_fatal(dev, err,
+				"guest requested %u queues, exceeding the maximum of %u.",
+				requested_num_queues, xenblk_max_queues);
+		return -ENOSYS;
 	}
 	be->blkif->nr_rings = requested_num_queues;
 	if (xen_blkif_alloc_rings(be->blkif))
-- 
2.6.6