[RFC PATCH] advapi32: Use Windows APIs to read /dev/urandom.

[Jacek Caban]

Hi Hans,


On 04/09/2020 13:15, Hans Leidekker wrote:
> This will cause a performance regression. SystemFunction036 (RtlGenRandom)
> is already an order of magnitude slower than native because it opens and closes
> /dev/urandom on every call. Going through wineserver makes it 2 orders of
> magnitude slower:
>
> int buf[4], i;
> for (i = 0; i < 100000; i++) RtlGenRandom(buf, sizeof(buf));
>
> Windows:                      16 ticks
> Wine/open():                 209 ticks
> Wine/NtCreateFile():        3612 ticks
> Wine/NtCreateFile()/cached:   96 ticks
>
> We could cache the file handle to mitigate that, but then there's the risk that
> an application accidentally closes the handle.


The difference would be probably even larger with NtClose() calls. 
Caching the handle seems good to me. With that, it's essentially a 
wrapped read syscall. To go beyond that, you could try to read larger 
chunks and cache the data.


Is there /dev/urandom equivalent on Windows? I'm wondering if a 
create_unix_device-based solution similar to /dev/null handling would be 
suitable to expose /dev/urandom as a Windows file.


Thanks,

Jacek