linux-kernel - Re: [Y2038] Question regarding support of old time interfaces beyond y2038

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Date:   Thu, 7 Mar 2019 15:43:10 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Zack Weinberg <zackw@...ix.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Joseph Myers <joseph@...esourcery.com>,
        GNU C Library <libc-alpha@...rceware.org>
Subject: Re: [Y2038] Question regarding support of old time interfaces
 beyond y2038

Hi Arnd,

> On Thu, Mar 7, 2019 at 8:53 AM Lukasz Majewski <lukma@...x.de> wrote:
> >
> > Hi Zack,
> >  
> > > On Tue, Mar 5, 2019 at 10:24 AM Lukasz Majewski <lukma@...x.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).  
> >
> > The question here is about the decision if even the old time APIs
> > shall be supported on 32 bit systems which are going to be Y2038
> > proof (like the 'stime').  
> 
> See my other reply. In the kernel, it won't be supported (the old
> syscall is of course still there, but we may have an option to remove
> all time32 interfaces). 

To be more specific:

I'm thinking of settimeofday/gettimeofday syscalls.

In the kernel we use internally do_sys_settimeofday64() to support
clock_settime() and settimeofday()

The internal (in-kernel) representation for those two is struct
timespec64.

If I may ask - why settimeofday64() and gettimeofday64() are not
implemented?

Is it because the same result can be achieved with clock_settime64(tv64)
+ settimeofday(NULL, tz) ?
(The drawback is two syscalls instead of one).




I've also stumbled upon the __kernel_timex introduction on the
playground branch:

"time: Add struct __kernel_timex"
2c620ff93d9fbd5d644760d4c21d389078ec1080

This one introduces the:
struct __kernel_timex_timeval {
	__kernel_time64_t tv_sec;
	long long tv_usec;
};

This code is "protected" by CONFIG_64BIT_TIME. 

Is there any plan to explicitly introduce:

struct __kernel_timeval {
       __kernel_time64_t tv_sec;
       long ong tv_usec;
}

and convert settimeofday()/gettimeofday() ?


Thanks in advance for your help.

> In glibc, it's probably there in a y2038-safe
> way since it is there now, other C libraries may take other decisions
> that are independent of y2038.
> 
>       Arnd




Best regards,

Lukasz Majewski

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