> -----Original Message-----
> From: Jan Beulich [mailto:jbeul...@suse.com]
> Sent: 24 October 2016 16:08
> To: Paul Durrant <paul.durr...@citrix.com>; Wei Liu <wei.l...@citrix.com>
> Cc: David Vrabel <david.vra...@citrix.com>; xen-de...@lists.xenproject.org;
> boris.ostrov...@oracle.com; Juergen Gross <jgr...@suse.com>;
> net...@vger.kernel.org
> Subject: [PATCH v2 RESEND] 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 <jbeul...@suse.com>
> ---
> v2: Avoid commit message to continue from subject.
> ---
> drivers/net/xen-netback/xenbus.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> --- 4.9-rc2/drivers/net/xen-netback/xenbus.c
> +++ 4.9-rc2-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)
Looking at other uses of xenbus_scanf() in the same code I think the check here
should be if (err < 0). It's a nit, since xenbus_scanf() cannot return 0, but
it would be better for consistency I think.
> 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);
> @@ -919,7 +919,7 @@ done:
> return 0;
>
> fail:
> - return err;
> + return err ?: -ENODATA;
I don't think you need this.
Paul
> }
>
> static void connect(struct backend_info *be)
>
>
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