Commit 7a9730af authored by Stuart Swales's avatar Stuart Swales Committed by Linus Torvalds
Browse files

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: default avatarStuart <Swales&lt;stuart.swales.croftnuisk@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2f09719a

fs/adfs/inode.c

+19 −21
Original line number Diff line number Diff line
@@ -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;

}



/*

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