Re: [Qemu-devel] [RFC v2 00/20] Memory API

Anthony Liguori
2011-06-27T15:37:45Z

On 06/27/2011 08:21 AM, Avi Kivity wrote:
> As expected, this is taking longer than expected, so I'm releasing something
> less complete than I'd have liked. Not even all of the PC machine is
> converted, but the difficult parts are (cirrus). It appears to work well.
>
> The major change compared to v1 is the introduction of
> memory_region_init_alias(), which defines a memory region in terms of another.
> With the current API, the ability to alias is provided by address arithmetic
> on ram_addr_t:
>
> ram_addr = qemu_ram_alloc(...);
> cpu_register_physical_memory(..., ram_addr, size, ...);
> /* alias: */
> cpu_register_physical_memory(..., ram_addr + offset, another_size, ...);
>
> With the new API, you have to create an alias:
>
> memory_region_init_ram(&mem, ...);
> memory_region_register_subregion(...,&mem);
> /* alias: */
> memory_region_init_alias(&alias, ...,&mem, offset, another_size);
> memory_region_register_subregion(...,&alias);

What's the rationale for explicit aliasing verses registering the same
region to two different address spaces?

Regards,

Anthony Liguori