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SubjectRe: [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@infradead.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

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