Date: Thu, 3 Dec 2020 22:05:53 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Cy Schubert <Cy.Schubert@cschubert.com> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-arch@freebsd.org Subject: Re: struct timex and Linux adjtimex() Message-ID: <X8lFIX8n7gKMoDk3@kib.kiev.ua> In-Reply-To: <202012031717.0B3HHalx003916@slippy.cwsent.com> References: <202012030523.0B35NsG7003810@slippy.cwsent.com> <X8i4UIzzH7vxkKvH@kib.kiev.ua> <60532.1606990671@critter.freebsd.dk> <X8i715mJUphnxXEo@kib.kiev.ua> <60612.1606991186@critter.freebsd.dk> <202012031717.0B3HHalx003916@slippy.cwsent.com>
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On Thu, Dec 03, 2020 at 09:17:36AM -0800, Cy Schubert wrote:
> In message <60612.1606991186@critter.freebsd.dk>, "Poul-Henning Kamp"
> writes:
> > --------
> > Konstantin Belousov writes:
> > > On Thu, Dec 03, 2020 at 10:17:51AM +0000, Poul-Henning Kamp wrote:
> > > > --------
> > > > Konstantin Belousov writes:
> > > >
> > > > > 1. Implement new syscall, which would take extended struct timex.
> > > > > ntp_adjtimex() perhaps should be kept for backward compatibility.
> > > > > [It does not matter where struct timeval is placed in the updated
> > > > > struct timex, see below].
> > > >
> > > > That would break all ports with timekeeping software.
> > > Why ?
> >
> > Last I looked they all had "#ifdef FreeBSD use ntp_adjtim()", so if
> > you rename it to ntp_adjtimex() you break them.
>
> There was no discussion about renaming ntp_adjtime() to ntp_adjtimex().
> ntp_adjtime() would remain. A new adjtimex() would be added.
As discussed, we should stay with ntp_adjtime(), it seems.
Libc may provide adjtimex() as an alias if this makes some porting easier.
BTW, I can code the syscall and compat layers, if this would make thinks
easier for everybody. I can do the addition of the actual flag if you
describe the semantic in more details.
I see the description of ADJ_SETOFFSET in the Linux adjtimex(2) man page:
ADJ_SETOFFSET (since Linux 2.6.39)
Add buf.time to the current time. If buf.status includes the
ADJ_NANO flag, then buf.time.tv_usec is interpreted as a
nanosecond value; otherwise it is interpreted as microseconds.
The value of buf.time is the sum of its two fields, but the
field buf.time.tv_usec must always be nonnegative. The follow‐
ing example shows how to normalize a timeval with nanosecond
resolution.
while (buf.time.tv_usec < 0) {
buf.time.tv_sec -= 1;
buf.time.tv_usec += 1000000000;
}
I do not quite understand the context and internal meaning of the second
paragraph, though. Kernel should not allow negative tv_usec as the input
parameter, right ?
>
> >
> > I see no problem having a #define to alias timex() to ntp_adjtime(),
> > but I doubt it would make life easier for anybody. (I think we used
> > to have that and it got GC'ed.)
> >
> > *If* we want to do this, the right way is to extend struct timex and
> > let ntpadjtime(2) handle the new modes.
> >
> > --
> > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> > phk@FreeBSD.ORG | TCP/IP since RFC 956
> > FreeBSD committer | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by incompetence.
>
>
> --
> Cheers,
> Cy Schubert <Cy.Schubert@cschubert.com>
> FreeBSD UNIX: <cy@FreeBSD.org> Web: https://FreeBSD.org
> NTP: <cy@nwtime.org> Web: https://nwtime.org
>
> The need of the many outweighs the greed of the few.
>
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