[PATCH] posix: Fix generic p{read,write}v buffer allocation (BZ#22457)

[Adhemerval Zanella]

On 23/11/2017 17:08, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> +  size_t mmap_size = ALIGN_UP (bytes, GLRO(dl_pagesize));
>> +  void *buffer = __mmap (NULL, mmap_size, PROT_READ | PROT_WRITE,
>> +		         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>> +  if (__glibc_unlikely (buffer == MAP_FAILED)
>> +      || __glibc_unlikely (!PTR_IS_ALIGNED (buffer, GLRO(dl_pagesize))))
>>      return -1;
> 
> I don't think POSIX requires that the length of the mapping is a
> multiple of the page size.  You could probably drop the alignment
> check, too, because I don't really see any reason why the alignment
> requirement would be related to the page size.
> 

Indeed we do not need to align to page size, however the alignment
requirement was the motivation to actually change its implementation
(check commit message for c79a72aa5cb8357c216a71015c7448a9259c8531).