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

[Anthony Liguori <anthony@codemonkey.ws>]

On 12/19/2011 09:04 AM, Avi Kivity wrote:
> On 12/19/2011 04:50 PM, Anthony Liguori wrote:
>>> +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.
>
> Why not?  It's legal according to the standards, if that's your concern
> (only _[_A-Z]+ are reserved).

http://www.gnu.org/s/hello/manual/libc/Reserved-Names.html

"In addition to the names documented in this manual, reserved names include all 
external identifiers (global functions and variables) that begin with an 
underscore (‘_’)"

Now that might just mean that you're shadowing a global name, so maybe that's 
okay, but I think it's easier to just enforce a consistent rule of, "don't start 
identifiers with an underscore".

>
>>> @@ -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.
>
> It's just prejudice, here's the call sequence:

It's not about whether it's fast or slow.  It's just unexpected.

Instead of returning a NULL pointer on error, you set .mr to NULL if an error 
occurs (which isn't documented by the comment btw).  Returning a pointer, or 
taking a pointer and returning a 0/-1 return value makes for a more consistent 
semantic with the rest of the code base.

Regards,

Anthony Liguori