Re: [PATCH] xen: check return value of xenbus_printf

Julien Grall
2015-10-15T18:21:44Z

Hi Insu,

On 15/10/15 19:12, Insu Yun wrote:
>
>
> On Thu, Oct 15, 2015 at 12:40 PM, David Vrabel <david.vrabel@citrix.com
> <mailto:david.vrabel@citrix.com>> wrote:
>
> On 15/10/15 17:25, Insu Yun wrote:
> > Internally, xenbus_printf uses memory allocation, so it can be failed in
> > memory pressure.Therefore, xenbus_printf's return should be checked
> > and properly handled.
> [...]
> > --- a/drivers/input/misc/xen-kbdfront.c
> > +++ b/drivers/input/misc/xen-kbdfront.c
> > @@ -129,8 +129,11 @@ static int xenkbd_probe(struct xenbus_device *dev,
> >
> > if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-abs-pointer", "%d", &abs) < 0)
> > abs = 0;
> > - if (abs)
> > - xenbus_printf(XBT_NIL, dev->nodename, "request-abs-pointer", "1");
> > + if (abs) {
> > + ret = xenbus_printf(XBT_NIL, dev->nodename, "request-abs-pointer", "1");
> > + if (ret)
>
> > + pr_warning("xenkbd: can't request abs-pointer");
>
>
> This error handling is from other code .
> I am not sure that it is right error handling.
>
>
>
> I think you want abs = 0 here or input device will be configured as
> absolute but the backend will supply relative coordinates.
>
>
> I cannot understand

If the frontend is not able to write the node "request-abs-pointer" in
the xenstore, the backend will always supply relative coordinates.

Although, as abs = 1, the frontend will be configured to handle absolute
coordinate. So the backend and frontend won't be able to understand each
other.

So you have to set abs to 0 if xebus_printf fails.

Regards,

--
Julien Grall