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@oracle.com
Cc: roger.pau@citrix.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 3cc6d1d86f1efc038f451dab3bb3452bed7de92b..415e79b69d347b207f4e1caeecc7e4ce482356d4 100644 (file)
--- 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))