Re: [Xen-devel] [Qemu-devel] [PATCH 01/23] memory: introduce memory_region_find()

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

On 12/19/2011 08:13 AM, Avi Kivity wrote:
> Given an address space (represented by the top-level memory region),
> returns the memory region that maps a given range.  Useful for implementing
> DMA.
>
> The implementation is a simplistic binary search.  Once we have a tree
> representation this can be optimized.
>
> Signed-off-by: Avi Kivity<avi@xxxxxxxxxx>
> ---
>   memory.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   memory.h |   32 ++++++++++++++++++++++++++++++++
>   2 files changed, 94 insertions(+), 0 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index cbd6988..d8b7c27 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -514,6 +514,20 @@ static void as_io_ioeventfd_del(AddressSpace *as, 
> MemoryRegionIoeventfd *fd)
>       .ops =&address_space_ops_io,
>   };
>
> +static AddressSpace *memory_region_to_address_space(MemoryRegion *mr)
> +{
> +    while (mr->parent) {
> +        mr = mr->parent;
> +    }
> +    if (mr == address_space_memory.root) {
> +        return&address_space_memory;
> +    }
> +    if (mr == address_space_io.root) {
> +        return&address_space_io;
> +    }
> +    abort();
> +}
> +
>   /* Render a memory region into the global view.  Ranges in @view obscure
>    * ranges in @mr.
>    */
> @@ -1309,6 +1323,54 @@ void memory_region_del_subregion(MemoryRegion *mr,
>       memory_region_update_topology();
>   }
>
> +static int cmp_flatrange_addr(const void *_addr, const void *_fr)
> +{
> +    const AddrRange *addr = _addr;
> +    const FlatRange *fr = _fr;
Please don't prefix with an underscore.

> +
> +    if (int128_le(addrrange_end(*addr), fr->addr.start)) {
> +        return -1;
> +    } else if (int128_ge(addr->start, addrrange_end(fr->addr))) {
> +        return 1;
> +    }
> +    return 0;
> +}
> +
> +static FlatRange *address_space_lookup(AddressSpace *as, AddrRange addr)
> +{
> +    return bsearch(&addr, as->current_map.ranges, as->current_map.nr,
> +                   sizeof(FlatRange), cmp_flatrange_addr);
> +}
> +
> +MemoryRegionSection memory_region_find(MemoryRegion *address_space,
> +                                       target_phys_addr_t addr, uint64_t size)
> +{
> +    AddressSpace *as = memory_region_to_address_space(address_space);
> +    AddrRange range = addrrange_make(int128_make64(addr),
> +                                     int128_make64(size));
> +    FlatRange *fr = address_space_lookup(as, range);
> +    MemoryRegionSection ret = { .mr = NULL };
> +
> +    if (!fr) {
> +        return ret;
> +    }
> +
> +    while (fr>  as->current_map.ranges
> +&&  addrrange_intersects(fr[-1].addr, range)) {
> +        --fr;
> +    }
> +
> +    ret.mr = fr->mr;
> +    range = addrrange_intersection(range, fr->addr);
> +    ret.offset_within_region = fr->offset_in_region;
> +    ret.offset_within_region += int128_get64(int128_sub(range.start,
> +                                                        fr->addr.start));
> +    ret.size = int128_get64(range.size);
> +    ret.offset_within_address_space = int128_get64(range.start);
> +    return ret;
> +}
> +
> +
>   void set_system_memory_map(MemoryRegion *mr)
>   {
>       address_space_memory.root = mr;
> diff --git a/memory.h b/memory.h
> index beae127..1d5c414 100644
> --- a/memory.h
> +++ b/memory.h
> @@ -146,6 +146,24 @@ struct MemoryRegionPortio {
>
>   #define PORTIO_END_OF_LIST() { }
>
> +typedef struct MemoryRegionSection MemoryRegionSection;
> +
> +/**
> + * MemoryRegionSection: describes a fragment of a #MemoryRegion
> + *
> + * @mr: the region, or %NULL if empty
> + * @offset_within_region: the beginning of the section, relative to @mr's start
> + * @size: the size of the section; will not exceed @mr's boundaries
> + * @offset_within_address_space: the address of the first byte of the section
> + *     relative to the region's address space
> + */
> +struct MemoryRegionSection {
> +    MemoryRegion *mr;
> +    target_phys_addr_t offset_within_region;
> +    uint64_t size;
> +    target_phys_addr_t offset_within_address_space;
> +};
> +
>   /**
>    * memory_region_init: Initialize a memory region
>    *
> @@ -502,6 +520,20 @@ void memory_region_del_subregion(MemoryRegion *mr,
>                                    MemoryRegion *subregion);
>
>   /**
> + * memory_region_find: locate a MemoryRegion in an address space
> + *
> + * Locates the first #MemoryRegion within an address space given by
> + * @address_space that overlaps the range given by @addr and @size.
> + *
> + * @address_space: a top-level (i.e. parentless) region that contains
> + *       the region to be found
> + * @addr: start of the area within @address_space to be searched
> + * @size: size of the area to be searched
> + */
> +MemoryRegionSection memory_region_find(MemoryRegion *address_space,
> +                                       target_phys_addr_t addr, uint64_t size);
Returning structs by value is a bit unexpected.

Otherwise, the patch looks good.

Regards,

Anthony Liguori

> +
> +/**
>    * memory_region_transaction_begin: Start a transaction.
>    *
>    * During a transaction, changes will be accumulated and made visible

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