The patch titled
adfs: improve timestamp precision
has been added to the -mm tree. Its filename is
adfs-improve-timestamp-precision.patch
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------------------------------------------------------
Subject: adfs: improve timestamp precision
From: Stuart Swales <stuart.swales.croftnuisk@xxxxxxxxx>
ADFS (FileCore) storage complies with the RISC OS timestamp specification
(40-bit centiseconds since 01 Jan 1900 00:00:00). It is desirable that
stored timestamp precision be maintained to facilitate a precise copy of
data and metadata from a hard disc (or image thereof) into a RISC OS
emulator (such as RPCEmu).
This patch implements a full-precision conversion from ADFS to Unix
timestamp as the existing driver, for ease of calculation with old 32-bit
compilers, uses the common trick of shifting the 40-bits representing
centiseconds around into 32-bits representing seconds thereby losing
precision.
Signed-off-by: Stuart Swales<stuart.swales.croftnuisk@xxxxxxxxx>
Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/adfs/inode.c | 42 ++++++++++++++++++++----------------------
1 file changed, 20 insertions(+), 22 deletions(-)
diff -puN fs/adfs/inode.c~adfs-improve-timestamp-precision fs/adfs/inode.c
--- a/fs/adfs/inode.c~adfs-improve-timestamp-precision
+++ a/fs/adfs/inode.c
@@ -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;
}
/*
_
Patches currently in -mm which might be from stuart.swales.croftnuisk@xxxxxxxxx are
adfs-fix-e-f-dir-size-2048-crashing-kernel.patch
adfs-improve-timestamp-precision.patch
adfs-add-hexadecimal-filetype-suffix-option.patch
adfs-remove-the-big-kernel-lock.patch
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