linux-kernel - Re: [PATCH v3 0/7] Isolate time_t data types for clock/timer syscalls

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Date:   Mon, 26 Jun 2017 11:17:13 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3 0/7] Isolate time_t data types for clock/timer syscalls

On Sun, Jun 25, 2017 at 7:35 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Sat, Jun 24, 2017 at 11:45:01AM -0700, Deepa Dinamani wrote:
>> The series aims at isolating data conversions of time_t based structures:
>> struct timespec and struct itimerspec at user space boundaries.
>> This helps to later change the underlying types to handle y2038 changes
>> to these.
>
> Nice...  A few questions:
>
> * what about setitimer(2)?  Right now that's the only remaining user of
> get_compat_itimerval(); similar for getitimer(2) and put_compat_itimerval().

We do not plan to support these beyond y2038 on 32 bit systems.
timer_settime() and timer_gettime() are considered to be replacements
for these, respectively.

There is also going to be a cleanup of timeval/ timespec/ time_t data
types and apis after the new syscalls are ready.
At that time I might choose to get rid of these itimerval apis. I'm
not sure yet.

> * you have two callers of get_compat_itimerspec64(); one is followed by
> itimerspec64_valid(), another - by its open-coded analogue.  The same
> goes for get_itimerspec64(); wouldn't it be better to have both check
> the validity immediately and simply fail with -EINVAL?  Matter of taste,
> but...

This is what I thought also. And, in fact this is how I had it in one
of the earlier version of my series.
But, the utimensat(2) is what I consider provides a counter example of
why this is a bad idea.
There is no reason you should not be able to read the itimerspec64 and
not check for validity soon after. Meaning there can be special
markers like UTIME_NOW and UTIME_OMIT in the nanosecond field which
will make the validity check fail. But, is perfectly normal for the
syscall under consideration.

> * should __sys_recvmmsg() switch to timespec64?

Socket timestamps will be handled in a different series. These could
be done a few ways like adding a new flag to recv syscall variants or
defining new timestamp types. The above call will be changed at that
time.

-Deepa