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

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Message-ID: <CABeXuvrO5XLD5QhBPui-v_G6JX=FgcaZLOL0C6B40f4oCyqOWg@mail.gmail.com>
Date:   Mon, 14 May 2018 10:25:06 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        anton@...era.com, Felipe Balbi <balbi@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        David Howells <dhowells@...hat.com>,
        David Sterba <dsterba@...e.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Christoph Hellwig <hch@....de>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Mike Marshall <hubcap@...ibond.com>, Jan Kara <jack@...e.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Jan Harkes <jaharkes@...cmu.edu>, Jiri Slaby <jslaby@...e.com>,
        Mark Fasheh <mark@...heh.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Nicolas Pitre <nico@...aro.org>,
        reiserfs-devel@...r.kernel.org,
        Richard Weinberger <richard@....at>,
        Sage Weil <sage@...hat.com>, Steve French <sfrench@...ba.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Tejun Heo <tj@...nel.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        "Ted Ts'o" <tytso@....edu>
Subject: Re: [PATCH 6/6] vfs: change inode times to use struct timespec64

On Mon, May 14, 2018 at 9:30 AM, Kees Cook <keescook@...omium.org> wrote:
> On Sun, May 13, 2018 at 9:05 PM, Deepa Dinamani <deepa.kernel@...il.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