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From: Deepa Dinamani <deepa.kernel@gmail.com>
Date: Mon, 14 May 2018 10:25:06 -0700
Message-ID: <CABeXuvrO5XLD5QhBPui-v_G6JX=FgcaZLOL0C6B40f4oCyqOWg@mail.gmail.com>
Subject: Re: [PATCH 6/6] vfs: change inode times to use struct timespec64
To: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
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On Mon, May 14, 2018 at 9:30 AM, Kees Cook <keescook@chromium.org> wrote:
> On Sun, May 13, 2018 at 9:05 PM, Deepa Dinamani <deepa.kernel@gmail.com> 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.

-Deepa