linux-kernel - Re: [PATCH v8 08/20] adfs: Fill in max and min timestamps in sb

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Message-ID: <CABeXuvoLHW2fYSNVC=N9tfNRtuq8Xg3QmqfcfMJEsCN5rEvuog@mail.gmail.com>
Date:   Tue, 20 Aug 2019 16:55:44 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v8 08/20] adfs: Fill in max and min timestamps in sb

On Tue, Aug 20, 2019 at 9:28 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Sun, Aug 18, 2019 at 09:58:05AM -0700, Deepa Dinamani wrote:
> > Note that the min timestamp is assumed to be
> > 01 Jan 1970 00:00:00 (Unix epoch). This is consistent
> > with the way we convert timestamps in adfs_adfs2unix_time().
>
> That's not actually correct.  RISC OS timestamps are centiseconds since
> 1900 stored in 5 bytes.

The timestamp can hold earlier values but the fs implementation
explicitly rejects those in adfs_adfs2unix_time() too_early check.
We could fix the implementation to not throw away times before 1970.
Are you suggesting we want to do this?
I could post a separate patch to fix this or we could do it as part of
the series.

 static void
 adfs_adfs2unix_time(struct timespec64 *tv, struct inode *inode)
 {
         unsigned int high, low;
         static const s64 nsec_unix_epoch_diff_risc_os_epoch =
RISC_OS_EPOCH_DELTA * NSEC_PER_SEC;
         s64 nsec;

         if (!adfs_inode_is_stamped(inode))
                 goto cur_time;

         high = ADFS_I(inode)->loadaddr & 0xFF; /* top 8 bits of timestamp */
         low  = ADFS_I(inode)->execaddr;    /* bottom 32 bits of timestamp */

         /* convert 40-bit centi-seconds to 32-bit seconds
          * going via nanoseconds to retain precision
          */
         nsec = (((s64) high << 32) | (s64) low) * 10000000; /* cs to ns */

         /* Files dated pre  01 Jan 1970 00:00:00. */
         if (nsec < nsec_unix_epoch_diff_risc_os_epoch)
                 goto too_early;

         /* convert from RISC OS to Unix epoch */
         nsec -= nsec_unix_epoch_diff_risc_os_epoch;

         *tv = ns_to_timespec64(nsec);
         return;

  cur_time:
         *tv = current_time(inode);
         return;

  too_early:
         tv->tv_sec = tv->tv_nsec = 0;
         return;
 }

-Deepa