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

[Kees Cook]

On Mon, May 14, 2018 at 11:23 AM, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote:
> 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.

Okay, fair enough. :) I will get my pstore v2 ready with casts. Thanks!

-Kees

-- 
Kees Cook
Pixel Security