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adfs: improve timestamp precision 

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@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Stuart Swales 2011-03-22 16:35:05 -07:00 committed by Linus Torvalds
parent 2f09719af7
commit 7a9730af9c
1 changed files with 19 additions and 21 deletions
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40
fs/adfs/inode.c
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@ -174,50 +174,48 @@ adfs_mode2atts(struct super_block *sb, struct inode *inode)
/*
* 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;
/* convert from RISC OS to Unix epoch */
nsec -= nsec_unix_epoch_diff_risc_os_epoch;
/* 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;
*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;
}
/*