Re: [Qemu-devel] [PATCH RFC v2 1/2] memory: allow MemoryRegion's priority field to accept negative values

[Peter Maydell]

On 9 September 2013 12:11, Marcel Apfelbaum <address@hidden> wrote:
> Priority is used to make visible some subregions by obscuring
> the parent MemoryRegion addresses overlapping with the subregion.
>
> By allowing the priority to be negative the opposite can be done:
> Allow a subregion to be visible on all the addresses not covered
> by the parent MemoryRegion or other subregions.
>
> Signed-off-by: Marcel Apfelbaum <address@hidden>
> ---
>  include/exec/memory.h | 6 +++---
>  memory.c              | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index ebe0d24..6995087 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -153,7 +153,7 @@ struct MemoryRegion {
>      bool flush_coalesced_mmio;
>      MemoryRegion *alias;
>      hwaddr alias_offset;
> -    unsigned priority;
> +    int priority;
>      bool may_overlap;
>      QTAILQ_HEAD(subregions, MemoryRegion) subregions;
>      QTAILQ_ENTRY(MemoryRegion) subregions_link;
> @@ -193,7 +193,7 @@ struct MemoryListener {
>      void (*coalesced_mmio_del)(MemoryListener *listener, MemoryRegionSection 
> *section,
>                                 hwaddr addr, hwaddr len);
>      /* Lower = earlier (during add), later (during del) */
> -    unsigned priority;
> +    int priority;

You haven't addressed any of the points I made reviewing
the first version of this. Please don't just ignore
code review, or people will stop reviewing your code.

I think it would also be nice to update docs/memory.txt
to say explicitly that priority is signed and why this
is useful, something like this:

====begin====
Priority values are signed, and the default value is
zero. This means that you can use
memory_region_add_subregion_overlap() both to specify
a region that must sit 'above' any others (with a
positive priority) and also a background region that
sits 'below' others (with a negative priority).
====endit====

(in the 'Overlapping regions and priority' section
of that document).

thanks
-- PMM