Re: [Xen-devel] [PATCH v5 03/10] IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.05.16 at 17:34, <quan.xu@xxxxxxxxx> wrote:
> On May 23, 2016 10:19 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >>> On 18.05.16 at 10:08, <quan.xu@xxxxxxxxx> wrote:
>> > +                                        unsigned long type,
>> > +                                        int preemptible)
>> >  {
>> >      unsigned long nx, x, y = page->u.inuse.type_info;
>> > -    int rc = 0;
>> > +    int rc = 0, ret = 0;
>> >
>> >      ASSERT(!(type & ~(PGT_type_mask | PGT_pae_xen_l2)));
>> >
>> > @@ -2578,11 +2579,11 @@ static int __get_page_type(struct page_info
>> *page, unsigned long type,
>> >          if ( d && is_pv_domain(d) && unlikely(need_iommu(d)) )
>> >          {
>> >              if ( (x & PGT_type_mask) == PGT_writable_page )
>> > -                iommu_unmap_page(d, mfn_to_gmfn(d, page_to_mfn(page)));
>> > +                ret = iommu_unmap_page(d, mfn_to_gmfn(d,
>> > + page_to_mfn(page)));
>> >              else if ( type == PGT_writable_page )
>> > -                iommu_map_page(d, mfn_to_gmfn(d, page_to_mfn(page)),
>> > -                               page_to_mfn(page),
>> > -                               IOMMUF_readable|IOMMUF_writable);
>> > +                ret = iommu_map_page(d, mfn_to_gmfn(d, page_to_mfn(page)),
>> > +                                     page_to_mfn(page),
>> > +
>> > + IOMMUF_readable|IOMMUF_writable);
>> >          }
>> >      }
>> >
>> > @@ -2599,6 +2600,9 @@ static int __get_page_type(struct page_info
>> *page, unsigned long type,
>> >      if ( (x & PGT_partial) && !(nx & PGT_partial) )
>> >          put_page(page);
>> >
>> > +    if ( !rc )
>> > +        rc = ret;
>> 
>> I know I've seen this a couple of time already, but with the special purpose 
>> of
>> "ret" I really wonder whether a more specific name wouldn't be warranted -
>> e.g. "iommu_rc" or "iommu_ret".
> 
> 
> rc is return value for this function, and no directly association with IOMMU 
> related code ( rc is only for alloc_page_type() ).
> So the rc cannot be "iommu_rc"..
> 
> ret can be "iommu_ret", but I think the pair 'rc' / 'ret' may look good.

Well, I'm not entirely opposed to keeping the names, but I continue
to think that while at the call sites the shorter name is reasonable, it
is quite a bit less clear at the point where you conditionally update rc.

Jan


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