Re: [Qemu-devel] [PATCH RFC 1/3] memory: allow MemoryRegion's priority field to accept negative values

[Peter Maydell]

On 2 September 2013 15:13, 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.

This comment is not exactly accurate. Allowing priority to
be signed is just a convenience: you can achieve exactly
the same effect by specifying some positive priority for
everything you map into the region and having the background
region be priority zero. (If you care at all about priorities
then everything being mapped into the region should be
happening under the control of your code anyway.)


> 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;

This is unrelated to MemoryRegion priorities -- it controls the
order in which listener callbacks are called. Don't try to change
both at once (and you only need the MR priorities anyway.)

>      AddressSpace *address_space_filter;
>      QTAILQ_ENTRY(MemoryListener) link;
>  };
> @@ -779,7 +779,7 @@ void memory_region_add_subregion(MemoryRegion *mr,
>  void memory_region_add_subregion_overlap(MemoryRegion *mr,
>                                           hwaddr offset,
>                                           MemoryRegion *subregion,
> -                                         unsigned priority);
> +                                         int priority);
>
>  /**
>   * memory_region_get_ram_addr: Get the ram address associated with a memory
> diff --git a/memory.c b/memory.c
> index 886f838..dfb3ae6 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1473,7 +1473,7 @@ void memory_region_add_subregion(MemoryRegion *mr,
>  void memory_region_add_subregion_overlap(MemoryRegion *mr,
>                                           hwaddr offset,
>                                           MemoryRegion *subregion,
> -                                         unsigned priority)
> +                                         int priority)
>  {
>      subregion->may_overlap = true;
>      subregion->priority = priority;

This isn't a complete set of changes. For instance
memory_region_set_address() has a local variable 'priority'
which should be signed now.

sysbus_mmio_map_common() and sysbus_mmio_map_overlap()
have priority arguments which need to change to match.

thanks
-- PMM