linux-kernel - [PATCH v2 2/4] xen-blkback: prefer xenbus_scanf() over xenbus

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Message-Id: <577FB80E02000078000FCA1B@prv-mh.provo.novell.com>
Date:	Fri, 08 Jul 2016 06:26:22 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Roger Pau Monne" <roger.pau@...rix.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	<david.vrabel@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, "Juergen Gross" <JGross@...e.com>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2 2/4] xen-blkback: prefer xenbus_scanf() over
 xenbus_gather()

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@...e.com>
Acked-by: Roger Pau Monné <roger.pau@...rix.com>
---
v2: Avoid commit message to continue from subject.
---
 drivers/block/xen-blkback/xenbus.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- 4.7-rc6-prefer-xenbus_scanf.orig/drivers/block/xen-blkback/xenbus.c
+++ 4.7-rc6-prefer-xenbus_scanf/drivers/block/xen-blkback/xenbus.c
@@ -1022,9 +1022,9 @@ static int connect_ring(struct backend_i
 	pr_debug("%s %s\n", __func__, dev->otherend);
 
 	be->blkif->blk_protocol = BLKIF_PROTOCOL_DEFAULT;
-	err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
-			    "%63s", protocol, NULL);
-	if (err)
+	err = xenbus_scanf(XBT_NIL, dev->otherend, "protocol",
+			   "%63s", protocol);
+	if (err <= 0)
 		strcpy(protocol, "unspecified, assuming default");
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_NATIVE))
 		be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
@@ -1036,10 +1036,9 @@ static int connect_ring(struct backend_i
 		xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
 		return -ENOSYS;
 	}
-	err = xenbus_gather(XBT_NIL, dev->otherend,
-			    "feature-persistent", "%u",
-			    &pers_grants, NULL);
-	if (err)
+	err = xenbus_scanf(XBT_NIL, dev->otherend,
+			   "feature-persistent", "%u", &pers_grants);
+	if (err <= 0)
 		pers_grants = 0;
 
 	be->blkif->vbd.feature_gnt_persistent = pers_grants;