Re: [PATCH] adfs: improve timestamp precision

From: Stuart Swales
Date: Fri Jan 21 2011 - 08:46:49 EST



[Thanks Andrew - icedove had screwed up the patch somewhat. I'm using
alpine to send this (have tested that it went round the loop ok and
produces the same patch)]

diff -uprN -X linux-2.6.37-vanilla/Documentation/dontdiff linux-2.6.37-vanilla/fs/adfs/inode.c linux-2.6.37-sks-adfs/fs/adfs/inode.c
--- linux-2.6.37-vanilla/fs/adfs/inode.c 2011-01-05 00:50:19.000000000 +0000
+++ linux-2.6.37-sks-adfs/fs/adfs/inode.c 2011-01-12 17:08:19.000000000 +0000
@@ -175,50 +175,48 @@ adfs_mode2atts(struct super_block *sb, s

/*
* Convert an ADFS time to Unix time. ADFS has a 40-bit centi-second time
- * referenced to 1 Jan 1900 (til 2248)
+ * referenced to 1 Jan 1900 (til 2248) so we need to discard 2208988800 seconds
+ * of time to convert from RISC OS epoch to Unix epoch.
*/
static void
adfs_adfs2unix_time(struct timespec *tv, struct inode *inode)
{
unsigned int high, low;
+ /* 01 Jan 1970 00:00:00 (Unix epoch) as nanoseconds since
+ * 01 Jan 1900 00:00:00 (RISC OS epoch)
+ */
+ static const s64 nsec_unix_epoch_diff_risc_os_epoch =
+ 2208988800000000000LL;
+ s64 nsec;

if (ADFS_I(inode)->stamped == 0)
goto cur_time;

- high = ADFS_I(inode)->loadaddr << 24;
- low = ADFS_I(inode)->execaddr;
+ high = ADFS_I(inode)->loadaddr & 0xFF; /* top 8 bits of timestamp */
+ low = ADFS_I(inode)->execaddr; /* bottom 32 bits of timestamp */

- high |= low >> 8;
- low &= 255;
+ /* 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 (high < 0x336e996a)
+ if (nsec < nsec_unix_epoch_diff_risc_os_epoch)
goto too_early;

- /* Files dated post 18 Jan 2038 03:14:05. */
- if (high >= 0x656e9969)
- goto too_late;
-
- /* discard 2208988800 (0x336e996a00) seconds of time */
- high -= 0x336e996a;
-
- /* convert 40-bit centi-seconds to 32-bit seconds */
- tv->tv_sec = (((high % 100) << 8) + low) / 100 + (high / 100 << 8);
- tv->tv_nsec = 0;
+ /* convert from RISC OS to Unix epoch */
+ nsec -= nsec_unix_epoch_diff_risc_os_epoch;
+
+ *tv = ns_to_timespec(nsec);
return;

cur_time:
- *tv = CURRENT_TIME_SEC;
+ *tv = CURRENT_TIME;
return;

too_early:
tv->tv_sec = tv->tv_nsec = 0;
return;
-
- too_late:
- tv->tv_sec = 0x7ffffffd;
- tv->tv_nsec = 0;
- return;
}

/*


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