Re: [Qemu-devel] [RFC][PATCH 09/15] memory: Introduce address_space_lookup_region

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-05-06 16:39, Paolo Bonzini wrote:
> Il 06/05/2013 16:26, Jan Kiszka ha scritto:
>> This new service so far only replaces phys_page_find as public API. In a
>> follow-up step, it will return the effective memory region for the
>> specified address, i.e. after resolving what are currently sub-pages.
>> Moreover, it will also once encapsulate locking and reference counting
>> when we introduce BQL-free dispatching.
> 
> In my IOMMU rebase I have a similar function:
> 
> /* address_space_translate: translate an address range into an address space
>  * into a MemoryRegionSection and an address range into that section.
>  *
>  * @as: #AddressSpace to be accessed
>  * @addr: address within that address space
>  * @xlat: pointer to address within the returned memory region section's
>  * #MemoryRegion.
>  * @len: pointer to length
>  * @is_write: indicates the transfer direction
>  */
> MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
>                                              hwaddr *xlat, hwaddr *len,
>                                              bool is_write);
> 
> It wraps (actually, replaces) both phys_page_find and
> memory_region_section_addr.

Good, looks like we are heading in similar directions. What is the
purpose of len? When does is_write matter?

In a later step, this should become something like
address_space_get_region_ref (to be paired with memory_region_unref,
once done). So this one also takes care of incrementing the reference
counter or acquiring the BQL, as necessary. Currently, it asks the
caller to specify if the BQL is already held, but that will change.

Jan

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