Re: How to get system localtime/wall time from eBPF?

On Tue, Mar 21, 2023 at 10:27 AM Vincent Li <[email protected]> wrote:
>
> On Mon, Mar 20, 2023 at 2:57 PM Vincent Li <[email protected]> wrote:
> >
> > On Mon, Mar 20, 2023 at 10:15 AM Jesper Dangaard Brouer
> > <[email protected]> wrote:
> > >
> > >
> > > On 20/03/2023 16.33, Vincent Li wrote:
> > > >
> > > > if I have a XDP based firewall to block ip  access based on system
> > > > localtime/wall time, is it still impossible like what mentioned here
> > > > https://github.com/xdp-project/xdp-tutorial/issues/204#issuecomment-819419800?
> > > > If so, is there any way to workaround this?
> > >
> > > You could use the BPF-helper named: bpf_ktime_get_tai_ns()
> > >
> > > See man clock_gettime(2). It is the same as CLOCK_TAI, which is
> > > (currently) offset with 37 sec to CLOCK_REALTIME which is wall-clock.
> > >
>
> sorry a follow-up question, the bpf_ktime_get_tai_ns will return time
> as nano seconds, right?
> I do not need the nanoseconds precision, I only need HH:MM like hours
> and minutes of the day, for example 10:30 = 10 * 60 + 30 is good
> enough,
>  any trick get that from bpf_ktime_get_tai_ns()
>

so I guess I just do bpf_ktime_get_tai_ns() / 60000000000  to convert
to  minutes ?

> > > Perhaps kernel should be extended with a bpf_ktime_get_wall_ns() ?
> > >
> > I guess it would be useful, I have a scenario that only allow ip
> > access between 07:00AM - 10:30PM for middle school kids everyday. now
> > I use cron job to run an user space program to add/delete IP from eBPF
> > map pinned by the XDP firewall program :)
> >
> > > --Jesper
> > >