[fulafel]

There's no standard for this - Linux folks came up & implemented it first and other platforms have taken that as compatibility target. So "non-portable implementation details" is all there is, and it works fine for CSPRNG.

[throwaway092834]

You're hinting that it's not in POSIX, and this is true.

There are many standards and cross-platform interfaces defined outside of POSIX. Some explicit and top-down, some organically evolved.

The spec for /dev/*random is here, as was published in the mid-90s: http://git.kernel.org/cgit/linux/kernel/git/stable/linux-sta...

[fulafel]

That's a comment block in the Linux random.c code titled "Theory of Operation"...

[throwaway092834]

Correct.