Re: [PATCH 6/6] vfs: change inode times to use struct timespec64

[Deepa Dinamani]

On Mon, May 14, 2018 at 10:53 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Mon, May 14, 2018 at 10:25 AM, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote:
>> On Mon, May 14, 2018 at 9:30 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> On Sun, May 13, 2018 at 9:05 PM, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote:
>>>> Kees mentioned that he wants to merge a patch to pstore that changes
>>>> it to use timespec64 internally for 4.17:
>>>> https://lkml.org/lkml/2018/5/13/3
>>>
>>> I'm still working on a v2 for pstore. What is the correct
>>> cross-architecture format string for timespec64's tv_sec? In your
>>> other patches, you're using %lld and a (long long) cast. I'd really
>>> like to avoid the need for casts.
>>
>> We cannot really avoid it for now.
>> struct timespec64 is defined this way for now:
>>
>> struct timespec {
>> __kernel_time_t tv_sec; /* seconds */
>> long tv_nsec; /* nanoseconds */
>> };
>>
>> #if __BITS_PER_LONG == 64
>> /* this trick allows us to optimize out timespec64_to_timespec */
>> # define timespec64 timespec
>>
>> #else
>>
>> struct timespec64 {
>> time64_t tv_sec; /* seconds */
>> long tv_nsec; /* nanoseconds */
>> };
>>
>> #endif
>>
>> This will all lead to tv_sec being long on a 64 bit architecture and
>> long long on a 32 bit architecture.
>> So there is no way of avoiding the cast for now.
>>
>> We plan to get rid of this trick and to have a single definition for
>> timespec64. But, that cleanup is planned for later when we cleanup all
>> struct timespec uses internally.
>
> Can we do something like:
>
> #if __BITS_PER_LONG == 64
> # define TVSEC_FMT "%ld"
> #else
> # define TVSEC_FMT "%lld"
> #endif
>
> so we can do stuff like:  sprintf(buf, "seconds: " KTIME_FMT, time->tv_sec)
>
> ? It seems easier to clean up than casts.

We have already introduced these casts in many places now.
It would be easier to do the clean up if they all follow a similar
pattern. ( I could probably write a coccinelle script that is not very
long).
But, it would be not much trouble if you wanted to follow this for pstore.

We also contemplated adding a format specifier for time. But, I think
we deferred it until we have a uniform way of using time internally.

-Deepa