Re: Getting time in realtime kernel driver

On 12.05.26 18:20, François Legal wrote:
> Hello,
> 
> I think I already asked about the same question some time ago, but I think I did not get a working answer, so here I am again.
> 
> On xenomai 3.2 + Ipipe (linux 5.4), I need to be able to get in a RT driver the current linux wall clock (impacted from NTP or PTP).
> I found out I get the correct value with ktime_get_real_ts64. Was willing to use __ktime_get_real_seconds but this one is not precise enought for my application.
> 
> So my question is : is it safe to use ktime_get_real_ts64 from within an RT driver ioctl function, and if not, which API in xenomai gives the exact same time as this one ?
> 

Nope, it's not safe, neither under legacy I-pipe (your kernel is dead
BTW) nor latest dovetail. Userspace access to the wallclock was hardened
for out-of-band accesses, but in-kernel had no use case, thus was never
considered.

For userland, the easiest answer is moving to a dovetail kernel and then
using CLOCK_REALTIME. Over I-pipe, we had to model this via a separate
clock named CLOCK_HOST_REALTIME.

Jan

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