On Wed, Apr 13, 2022 at 01:54:01PM +0200, Jason A. Donenfeld wrote:
The addition of random_get_entropy_fallback() provides access to whichever time source has the highest frequency, which is useful for gathering entropy on platforms without available cycle counters. It's not necessarily as good as being able to quickly access a cycle counter that the CPU has, but it's still something, even when it falls back to being jiffies-based. In the event that a given arch does not define get_cycles(), falling back to the get_cycles() default implementation that returns 0 is really not the best we can do. Instead, at least calling random_get_entropy_fallback() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though random_get_entropy_fallback() is super high precision or guaranteed to be entropic, but basically anything that's not zero all the time is better than returning zero all the time. Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Theodore Ts'o <tytso@xxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- include/linux/timex.h | 8 ++++++++ kernel/time/timekeeping.c | 10 ++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/timex.h b/include/linux/timex.h index 5745c90c8800..fbbe34226044 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -62,6 +62,8 @@ #include <linux/types.h> #include <linux/param.h> +extern unsigned long random_get_entropy_fallback(void);
Hi I'm surprised this didn't trigger checkpatch to warn. From coding-style: 6.1) Function prototypes Do not use the ``extern`` keyword with function declarations as this makes lines longer and isn't strictly necessary. Thanks! -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
