[Xen-devel] [PATCH v2 3/4] xen-blkfront: prefer xenbus_scanf() over xenbus_gather()

["Jan Beulich" <JBeulich@xxxxxxxx>]

For single items being collected this should be preferred as being more
typesafe (as the compiler can check format string and to-be-written-to
variable match) and more efficient (requiring one less parameter to be
passed).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
v2: Avoid commit message to continue from subject.
---
 drivers/block/xen-blkfront.c |   43 +++++++++++++++++++------------------------
 1 file changed, 19 insertions(+), 24 deletions(-)

--- 4.7-rc6-prefer-xenbus_scanf.orig/drivers/block/xen-blkfront.c
+++ 4.7-rc6-prefer-xenbus_scanf/drivers/block/xen-blkfront.c
@@ -2208,10 +2208,9 @@ static void blkfront_setup_discard(struc
                info->discard_granularity = discard_granularity;
                info->discard_alignment = discard_alignment;
        }
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                   "discard-secure", "%d", &discard_secure,
-                   NULL);
-       if (!err)
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "discard-secure", "%u", &discard_secure);
+       if (err > 0)
                info->feature_secdiscard = !!discard_secure;
 }
 
@@ -2310,9 +2309,8 @@ static void blkfront_gather_backend_feat
 
        info->feature_flush = 0;
 
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                       "feature-barrier", "%d", &barrier,
-                       NULL);
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "feature-barrier", "%d", &barrier);
 
        /*
         * If there's no "feature-barrier" defined, then it means
@@ -2321,38 +2319,35 @@ static void blkfront_gather_backend_feat
         *
         * If there are barriers, then we use flush.
         */
-       if (!err && barrier)
+       if (err > 0 && barrier)
                info->feature_flush = REQ_FLUSH | REQ_FUA;
        /*
         * And if there is "feature-flush-cache" use that above
         * barriers.
         */
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                       "feature-flush-cache", "%d", &flush,
-                       NULL);
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "feature-flush-cache", "%d", &flush);
 
-       if (!err && flush)
+       if (err > 0 && flush)
                info->feature_flush = REQ_FLUSH;
 
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                       "feature-discard", "%d", &discard,
-                       NULL);
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "feature-discard", "%d", &discard);
 
-       if (!err && discard)
+       if (err > 0 && discard)
                blkfront_setup_discard(info);
 
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                       "feature-persistent", "%u", &persistent,
-                       NULL);
-       if (err)
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "feature-persistent", "%d", &persistent);
+       if (err <= 0)
                info->feature_persistent = 0;
        else
                info->feature_persistent = persistent;
 
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-max-indirect-segments", "%u", 
&indirect_segments,
-                           NULL);
-       if (err)
+       err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+                          "feature-max-indirect-segments", "%u",
+                          &indirect_segments);
+       if (err <= 0)
                info->max_indirect_segments = 0;
        else
                info->max_indirect_segments = min(indirect_segments,



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