diff options
| author | Stuart Swales <stuart.swales.croftnuisk@gmail.com> | 2011-03-22 16:35:05 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-03-22 17:44:17 -0700 |
| commit | 7a9730af9c596749425a98eba136152e5be4602a (patch) | |
| tree | 1a7f03d7541768a9d2b4b25fab2ee07eec37c268 | |
| parent | 2f09719af705db56032ae480a2d9c32c2a3fcbd3 (diff) | |
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>
| -rw-r--r-- | fs/adfs/inode.c | 40 |
1 files changed, 19 insertions, 21 deletions
diff --git a/fs/adfs/inode.c b/fs/adfs/inode.c index 09fe40198d1c..16d7ef2dffe1 100644 --- a/fs/adfs/inode.c +++ b/fs/adfs/inode.c @@ -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; - - /* discard 2208988800 (0x336e996a00) seconds of time */ - high -= 0x336e996a; + /* convert from RISC OS to Unix epoch */ + nsec -= nsec_unix_epoch_diff_risc_os_epoch; - /* 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; } /* |