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Re: [Xen-devel] [PATCH for 4.7] Remove HVMMEM_mmio_write_dm from the public interface.

On Thu, Apr 28, 2016 at 07:40:45PM +0800, Yu, Zhang wrote:
> Thanks Jan. And I admire your rigorous thought. :)
> On 4/28/2016 6:57 PM, Jan Beulich wrote:
> >>>>On 28.04.16 at 12:42, <george.dunlap@xxxxxxxxxx> wrote:
> >>On 28/04/16 11:22, Jan Beulich wrote:
> >>>>>>On 28.04.16 at 10:29, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> >>>>@@ -5529,7 +5527,7 @@ long do_hvm_op(unsigned long op,
> >>>>             [HVMMEM_ram_rw]  = p2m_ram_rw,
> >>>>             [HVMMEM_ram_ro]  = p2m_ram_ro,
> >>>>             [HVMMEM_mmio_dm] = p2m_mmio_dm,
> >>>>-            [HVMMEM_mmio_write_dm] = p2m_mmio_write_dm
> >>>>+            [HVMMEM_unused] = p2m_invalid
> >>>
> >>>Why don't you simply delete the old line, without replacement?
> >>
> Well, I did not delete the old line, because in my coming patch(the
> p2m renaming code), I'm planning to introduce the HVMMEM_ioreq_server,
> which is HVMMEM_unused+1. And I do not want the check of a.hvmmem_type
> against HVMMEN_unused later in this routine appear in that patch.
> >>That might have been slightly cleaner; but we're going to have to put it
> >>back as soon as the development window opens anyway, so I don't really
> >>see the point of going through the effort of respinning the patch again.
> >>
> >>Would you be willing to ack this version anyway?
> >
> >I have no problem doing so (and in fact I have it on my to by
> >committed list already), it is just looked slightly confusing (and
> >I had already typed half a reply that this isn't what was discussed
> >until I properly looked at the next hunk), and hence I wanted to
> >understand the motivation. And btw., I'm not convinced it would
> >need to be put there anyway later: I don't view the used
> >mechanism as a good (read: extensible) one to deal with what
> >would be holes in the array above. Indeed we can't leave them
> >uninitialized (as that would mean p2m_ram_rw), but I think we
> >should better find a way to initialize _all_ unused slots without
> >requiring an initializer for each of them. Sadly the desire to allow
> >compilation with clang prohibits the most natural solution:
> >
> >        static const p2m_type_t memtype[] = {
> >            [0 ... <upper-bound> - 1] = p2m_invalid,
> Not sure if this will compile? Can have a try. :)

To answer your question this can compile with gcc but not probably not
with clang. This syntax is gcc extension.

See: https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html


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