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Date: Mon, 27 Jun 2011 10:37:42 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC v2 00/20] Memory API
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

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