Re: [Qemu-devel] [RFC] Memory API

[Avi Kivity <avi@redhat.com>]

On 05/18/2011 06:47 PM, Stefan Weil wrote:
>> I'm not a fan of having per-access type function pointers.
>
>
> Do you think of something like these declaration:
>
> typedef uint64_t (*MemoryReadFunc)(MemoryRegion *mr, 
> target_phys_addr_t addr, size_t size);
> typedef void (*MemoryWriteFunc)(MemoryRegion *mr, target_phys_addr_t 
> addr, uint64_t data, size_tsize);
>
> For 32 bit host / target, this would mean some unnecessary overhead.

Frankly, the overhead is pretty low.  I think we can neglect it.

>
> What about passing values by address:
>
> typedef void (*MemoryReadFunc)(MemoryRegion *mr, target_phys_addr_t 
> addr, void *data, size_t size);
> typedef void (*MemoryWriteFunc)(MemoryRegion *mr, target_phys_addr_t 
> addr, const void *data, size_t size);

Those void *s will be quite annoying.  Especially on hosts which don't 
allow misaligned data, you'll never know how to reference them.

>
> If we keep per-access type function pointers, they should use 
> individual prototypes
> for the different access types:
>
> typedef uint8_t  (*MemoryReadbFunc)(MemoryRegion *mr, 
> target_phys_addr_t addr);
> typedef uint16_t (*MemoryReadwFunc)(MemoryRegion *mr, 
> target_phys_addr_t addr);
> typedef uint32_t (*MemoryReadlFunc)(MemoryRegion *mr, 
> target_phys_addr_t addr);
> typedef uint64_t (*MemoryReadllFunc)(MemoryRegion *mr, 
> target_phys_addr_t addr);
> ...

I prefer having size as an argument.

Something else I though about:

    void memory_region_set_access_sizes(MemoryRegion *mr, int min, int max);

if, for example, min=2 and max=4, then byte accesses will be emulated as 
word accesses (RMW for writes) and quad accesses will be emulated as two 
long accesses.  So a device that emulates 32-bit registers can set 
min=max=4 and get all the other sizes for free.

-- 
error compiling committee.c: too many arguments to function