Re: [Qemu-devel] [PATCH] docs/memory.txt: Improve list of different memory regions

[Paolo Bonzini]

On 28/01/2016 19:54, Peter Maydell wrote:
> Improve the part of the memory region documentation which describes
> the various different kinds of memory region:
>  * add the missing types ROM, IOMMU and reservation
>  * mention the functions used to initialize each type, as a hint
>    for finding the API docs and examples of use
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  docs/memory.txt | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/memory.txt b/docs/memory.txt
> index 2ceb348..8745f76 100644
> --- a/docs/memory.txt
> +++ b/docs/memory.txt
> @@ -26,14 +26,28 @@ These represent memory as seen from the CPU or a device's 
> viewpoint.
>  Types of regions
>  ----------------
>  
> -There are four types of memory regions (all represented by a single C type
> +There are multiple types of memory regions (all represented by a single C 
> type
>  MemoryRegion):
>  
>  - RAM: a RAM region is simply a range of host memory that can be made 
> available
>    to the guest.
> +  You typically initialize these with memory_region_init_ram().  Some special
> +  purposes require the variants memory_region_init_resizeable_ram(),
> +  memory_region_init_ram_from_file(), or memory_region_init_ram_ptr().
>  
>  - MMIO: a range of guest memory that is implemented by host callbacks;
>    each read or write causes a callback to be called on the host.
> +  You initialize these with memory_region_io(), passing it a MemoryRegionOps
> +  structure describing the callbacks.
> +
> +- ROM: a ROM memory region works like RAM for reads (directly accessing
> +  a region of host memory), but like MMIO for writes (invoking a callback).
> +  You initialize these with memory_region_init_rom_device().
> +
> +- IOMMU region: an IOMMU region translates addresses of accesses made to it
> +  and forwards them to some other target memory region.  As the name 
> suggests,
> +  these are only needed for modelling an IOMMU, not for simple devices.
> +  You initialize these with memory_region_init_iommu().
>  
>  - container: a container simply includes other memory regions, each at
>    a different offset.  Containers are useful for grouping several regions
> @@ -45,12 +59,22 @@ MemoryRegion):
>    can overlay a subregion of RAM with MMIO or ROM, or a PCI controller
>    that does not prevent card from claiming overlapping BARs.
>  
> +  You initialize a pure container with memory_region_init().
> +
>  - alias: a subsection of another region.  Aliases allow a region to be
>    split apart into discontiguous regions.  Examples of uses are memory banks
>    used when the guest address space is smaller than the amount of RAM
>    addressed, or a memory controller that splits main memory to expose a "PCI
>    hole".  Aliases may point to any type of region, including other aliases,
>    but an alias may not point back to itself, directly or indirectly.
> +  You initialize these with memory_region_init_alias().
> +
> +- reservation region: a reservation region is primarily for debugging.
> +  It claims I/O space that is not supposed to be handled by QEMU itself.
> +  The typical use is to track parts of the address space which will be
> +  handled by the host kernel when KVM is enabled.
> +  You initialize these with memory_region_init_reservation(), or by
> +  passing a NULL callback parameter to memory_region_init_io().
>  
>  It is valid to add subregions to a region which is not a pure container
>  (that is, to an MMIO, RAM or ROM region). This means that the region
> 

Sorry, this missed today's pull request.  The patch is a fine
improvement, feel free to apply it directly.

Paolo