[PATCH v3] xen-netback: prefer xenbus_scanf() over xenbus_gather()

[PATCH v3] xen-netback: prefer xenbus_scanf() over xenbus_gather()

[Jan Beulich]

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@suse.com>
---
v3: For consistency with other code don't consider zero an error
    (utilizing that xenbus_scanf() at present won't return zero).
v2: Avoid commit message to continue from subject.
---
 drivers/net/xen-netback/xenbus.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- 4.9-rc4/drivers/net/xen-netback/xenbus.c
+++ 4.9-rc4-xen-netback-prefer-xenbus_scanf/drivers/net/xen-netback/xenbus.c
@@ -889,16 +889,16 @@ static int connect_ctrl_ring(struct back
 	unsigned int evtchn;
 	int err;
 
-	err = xenbus_gather(XBT_NIL, dev->otherend,
-			    "ctrl-ring-ref", "%u", &val, NULL);
-	if (err)
+	err = xenbus_scanf(XBT_NIL, dev->otherend,
+			   "ctrl-ring-ref", "%u", &val);
+	if (err < 0)
 		goto done; /* The frontend does not have a control ring */
 
 	ring_ref = val;
 
-	err = xenbus_gather(XBT_NIL, dev->otherend,
-			    "event-channel-ctrl", "%u", &val, NULL);
-	if (err) {
+	err = xenbus_scanf(XBT_NIL, dev->otherend,
+			   "event-channel-ctrl", "%u", &val);
+	if (err < 0) {
 		xenbus_dev_fatal(dev, err,
 				 "reading %s/event-channel-ctrl",
 				 dev->otherend);

RE: [PATCH v3] xen-netback: prefer xenbus_scanf() over xenbus_gather()

[Paul Durrant]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 08 November 2016 07:46
> To: Paul Durrant <Paul.Durrant@citrix.com>; Wei Liu <wei.liu2@citrix.com>
> Cc: xen-devel <xen-devel@lists.xenproject.org>; netdev@vger.kernel.org
> Subject: [PATCH v3] xen-netback: 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@suse.com>

LGTM

Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

> ---
> v3: For consistency with other code don't consider zero an error
>     (utilizing that xenbus_scanf() at present won't return zero).
> v2: Avoid commit message to continue from subject.
> ---
>  drivers/net/xen-netback/xenbus.c |   12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> --- 4.9-rc4/drivers/net/xen-netback/xenbus.c
> +++ 4.9-rc4-xen-netback-prefer-xenbus_scanf/drivers/net/xen-
> netback/xenbus.c
> @@ -889,16 +889,16 @@ static int connect_ctrl_ring(struct back
>  	unsigned int evtchn;
>  	int err;
> 
> -	err = xenbus_gather(XBT_NIL, dev->otherend,
> -			    "ctrl-ring-ref", "%u", &val, NULL);
> -	if (err)
> +	err = xenbus_scanf(XBT_NIL, dev->otherend,
> +			   "ctrl-ring-ref", "%u", &val);
> +	if (err < 0)
>  		goto done; /* The frontend does not have a control ring */
> 
>  	ring_ref = val;
> 
> -	err = xenbus_gather(XBT_NIL, dev->otherend,
> -			    "event-channel-ctrl", "%u", &val, NULL);
> -	if (err) {
> +	err = xenbus_scanf(XBT_NIL, dev->otherend,
> +			   "event-channel-ctrl", "%u", &val);
> +	if (err < 0) {
>  		xenbus_dev_fatal(dev, err,
>  				 "reading %s/event-channel-ctrl",
>  				 dev->otherend);
> 
> 

Re: [PATCH v3] xen-netback: prefer xenbus_scanf() over xenbus_gather()

[David Miller]

From: "Jan Beulich" <JBeulich@suse.com>
Date: Tue, 08 Nov 2016 00:45:53 -0700

> 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@suse.com>
> ---
> v3: For consistency with other code don't consider zero an error
>     (utilizing that xenbus_scanf() at present won't return zero).
> v2: Avoid commit message to continue from subject.

Applied to net-next, thanks.