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Re: [Y2038] Question regarding support of old time interfaces beyond y2038
- From: Zack Weinberg <zackw at panix dot com>
- To: Lukasz Majewski <lukma at denx dot de>
- Cc: Arnd Bergmann <arnd at arndb dot de>, Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, Joseph Myers <joseph at codesourcery dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 5 Mar 2019 11:05:52 -0500
- Subject: Re: [Y2038] Question regarding support of old time interfaces beyond y2038
- References: <20190305162351.5aadde66@jawa>
On Tue, Mar 5, 2019 at 10:24 AM Lukasz Majewski <lukma@denx.de> wrote:
> From other discussion [4] - regarding the following system calls:
> time, stime, gettimeofday, settimeofday, adjtimex, nanosleep, alarm,
> getitimer, setitimer, select, utime, utimes, futimesat, and
> {old,new}{l,f,}stat{,64}.
>
> "These all pass 32-bit time_t arguments on 32-bit
> architectures and are replaced by other interfaces (e.g. posix
> timers and clocks, statx). C libraries implementing 64-bit time_t in
> 32-bit architectures have to implement the handles by wrapping
> around the newer interfaces."
1) We should be clear that most of these will continue to be supported
as C library interfaces even if they are not system calls. Some of
them are obsolete enough and/or rarely used enough that we might not
bother (the older ways to set the system clock, for instance).
2) I know of one case where the new interfaces don't cover all of the
functionality of the old ones: timers started by setitimer continue to
run after an execve, timers started by timer_create don't. This means
setitimer(ITIMER_VIRTUAL) can be used to impose a CPU time limit on a
program you didn't write, and timer_create can't. If new kernels are
not going to have setitimer as a primitive, we need some other way of
getting the same effect.
zw