Re: [Xen-devel] [PATCH] xl: convert vcpuid to signed in main_vcpupin()

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On mer, 2014-09-03 at 14:52 +0100, Ian Campbell wrote:
> On Wed, 2014-08-20 at 17:36 +0200, Dario Faggioli wrote:
> > No functional changes, it just looks more correct, considering
> > that at some point in the function we assign -1 to it (and
> > at some other later point we check for it to be -1),
> 
> I think that's more than just "looks more correct", it's just wrong to
> compare an unsigned to -1, or to assign it.
> 
> And there may well be a functional change since gcc is no longer allowed
> to assume that the number is +ve and therefore cannot discard some of
> these checks any more. We are probably just lucky that gcc isn't doing
> so already (and unlucky that it isn't generating a warning...)
> 
Right, and thanks for all the details. :-)

Should I change the changelog, if I repost?

> > Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> > ---
> >  tools/libxl/xl_cmdimpl.c |   14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> > diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> > index f1c136a..a29a579 100644
> > --- a/tools/libxl/xl_cmdimpl.c
> > +++ b/tools/libxl/xl_cmdimpl.c
> > @@ -4601,8 +4601,9 @@ int main_vcpupin(int argc, char **argv)
> >      libxl_vcpuinfo *vcpuinfo;
> >      libxl_bitmap cpumap_hard, cpumap_soft;;
> >      libxl_bitmap *soft = &cpumap_soft, *hard = &cpumap_hard;
> > -    uint32_t vcpuid, domid;
> >      const char *vcpu, *hard_str, *soft_str;
> > +    uint32_t domid;
> > +    long vcpuid;
> 
> I think an int would be sufficiently large for this.
> 
The only reason why I used a long is that the function used to do the
actual conversion is strtol(), which returns a long. Strictly speaking,
if using an int, I think I should then be checking for the returned
value to be within [INT_MIN, INT_MAX] and error out if it's not.

That being said, we can probably use int and leave the range checking
alone, as, if someone tries to pin vCPU INT_MAX+1, he/she deserves all
the bad that will happen, but since I was polishing the code... :-P

Just let me know if you want it to be and int, and if you think the
range checking should be there, and I'll copy.

Thanks and regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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