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Re: [Xen-devel] [PATCH v2 39/52] xen: check parameter validity when parsing command line

On Tue, Aug 15, 2017 at 02:54:07PM +0200, Juergen Gross wrote:
> On 14/08/17 14:46, Jan Beulich wrote:
> >>>> On 14.08.17 at 09:08, <jgross@xxxxxxxx> wrote:
> >> --- a/xen/common/kernel.c
> >> +++ b/xen/common/kernel.c
> >>                      optval[-1] = '\0';
> >> +                    break;
> > 
> > Why? Applies to further break-s you add: At least in the past we
> > had command line options with two handlers, where each of them
> > needed to be invoked. I don't think we should make such impossible
> > even if right now there aren't any such examples. Yet if you really
> > mean to, then the behavioral change needs to be called out in the
> > description.
> While working on this I realized that this functionality has been
> working only in some cases. The custom parsing functions are being
> called with a copy of the option value, which they modify in some
> cases. So a second handler being called would see another value as
> the first handler, as long as modifying the option value keeps to be
> allowed.
> I see three possibilities here:
> 1. don't allow multiple handlers for the same parameter
> 2. restore the option value before calling each handler (as the
>    error message I'm adding with this patch requires access to the
>    whole option value this wouldn't be too hard)
> 3. don't allow a handler to modify the option value (solves my error
>    message problem, too)

Either 2 or 3 please.

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