Re: [Xen-devel] [PATCH 4/5] xen: events, exposes evtchn_alloc_unbound_domain

[Jean Guyader <jean.guyader@xxxxxxxxxx>]

On 09/08 11:40, Jean Guyader wrote:
> On 9 August 2012 11:35, Tim Deegan <tim@xxxxxxx> wrote:
> > At 11:23 +0100 on 09 Aug (1344511426), Ian Campbell wrote:
> >> On Thu, 2012-08-09 at 11:06 +0100, Tim Deegan wrote:
> >> > At 20:50 +0100 on 03 Aug (1344027053), Jean Guyader wrote:
> >> > >
> >> > > Exposes evtchn_alloc_unbound_domain to the rest of
> >> > > Xen so we can create allocated unbound evtchn within Xen.
> >> > >
> >> > > Signed-off-by: Jean Guyader <jean.guyader@xxxxxxxxxx>
> >> >
> >> > > @@ -161,18 +163,18 @@ static long 
> >> > > evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc)
> >> > >  {
> >> > >      struct evtchn *chn;
> >> > >      struct domain *d;
> >> > > -    int            port;
> >> > > +    evtchn_port_t  port;
> >> > >      domid_t        dom = alloc->dom;
> >> > > -    long           rc;
> >> > > +    int            rc;
> >> >
> >> > The function returns long; if you're tidying this up to be an int, might
> >> > as well change the return type too.
> >>
> >> I'm not sure if this is relevant but Jan just sent a patch to "make all
> >> (native) hypercalls consistently have "long" return type". I
> >> think/suspect this rc here turns into the result of the hypercall?
> >>
> >> Jan's patch was motivated by something to do with sign extension when a
> >> hypercall's int return is written to the long in the multicall arg
> >> struct which causes strangeness. Perhaps not totally relevant to
> >> evtchn_alloc which is unlikely to be in a MC.
> >
> > Yes, this eventually ends up in a hypercall handler, but s/long/int/
> > here doesn't cause problems because
> >  - rc is only ever set to an 'int' value here so we can't lose data
> >    from the type being too narrow; and
> >  - Those int values get cast up to long (either in here or in the
> >    caller) directly, which will sign-extend the.
> >
> > It really doesn't matter whether this function returns an int or a long,
> > but it's a bit untidy to change it half-way.
> >
> 
> The main reason why I changed it only base ERROR_EXIT_DOM expects an int based
> on the format string. I guess I could cast the long in int for the
> call to ERROR_EXIT_DOM
> but that doesn't really look nice either.
> 

Hi,

Here is a new version that should address the comments from Tim and Jan.

Signed-off-by: Jean Guyader <jean.guyader@xxxxxxxxxx>

Jean

Attachment: evtchn_alloc_unbound_domain.patch
Description: Text Data

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