/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2005
 *	Sleepycat Software.  All rights reserved.
 *
 * $Id: os_fid.c,v 12.4 2005/10/11 18:17:00 bostic Exp $
 */

#include "db_config.h"

#include "db_int.h"

#define	SERIAL_INIT	0
static u_int32_t fid_serial = SERIAL_INIT;

/*
 * __os_fileid --
 *	Return a unique identifier for a file.
 */
int
__os_fileid(dbenv, fname, unique_okay, fidp)
	DB_ENV *dbenv;
	const char *fname;
	int unique_okay;
	u_int8_t *fidp;
{
	db_threadid_t tid;
	pid_t pid;
	size_t i;
	u_int32_t tmp;
	u_int8_t *p;
	int ret;

	/*
	 * The documentation for GetFileInformationByHandle() states that the
	 * inode-type numbers are not constant between processes.  Actually,
	 * they are, they're the NTFS MFT indexes.  So, this works on NTFS,
	 * but perhaps not on other platforms, and perhaps not over a network.
	 * Can't think of a better solution right now.
	 */
	DB_FH *fhp;
	BY_HANDLE_FILE_INFORMATION fi;
	BOOL retval = FALSE;

	DB_ASSERT(fname != NULL);

	/* Clear the buffer. */
	memset(fidp, 0, DB_FILE_ID_LEN);

	/*
	 * Initialize/increment the serial number we use to help avoid
	 * fileid collisions.  Note that we don't bother with locking;
	 * it's unpleasant to do from down in here, and if we race on
	 * this no real harm will be done, since the finished fileid
	 * has so many other components.
	 *
	 * We use the bottom 32-bits of the process ID, hoping they
	 * are more random than the top 32-bits (should we be on a
	 * machine with 64-bit process IDs).
	 *
	 * We increment by 100000 on each call as a simple way of
	 * randomizing;  simply incrementing seems potentially less useful
	 * if pids are also simply incremented, since this is process-local
	 * and we may be one of a set of processes starting up.  100000
	 * pushes us out of pid space on most platforms, and has few
	 * interesting properties in base 2.
	 */
	if (fid_serial == SERIAL_INIT) {
		__os_id(dbenv, &pid, &tid);
		fid_serial = pid;
	} else
		fid_serial += 100000;

	/*
	 * First we open the file, because we're not given a handle to it.
	 * If we can't open it, we're in trouble.
	 */
	if ((ret = __os_open(dbenv, fname, DB_OSO_RDONLY, _S_IREAD, &fhp)) != 0)
		return (ret);

	/* File open, get its info */
	if ((retval = GetFileInformationByHandle(fhp->handle, &fi)) == FALSE)
		ret = __os_get_errno();
	(void)__os_closehandle(dbenv, fhp);

	if (retval == FALSE)
		return (ret);

	/*
	 * We want the three 32-bit words which tell us the volume ID and
	 * the file ID.  We make a crude attempt to copy the bytes over to
	 * the callers buffer.
	 *
	 * We don't worry about byte sexing or the actual variable sizes.
	 *
	 * When this routine is called from the DB access methods, it's only
	 * called once -- whatever ID is generated when a database is created
	 * is stored in the database file's metadata, and that is what is
	 * saved in the mpool region's information to uniquely identify the
	 * file.
	 *
	 * When called from the mpool layer this routine will be called each
	 * time a new thread of control wants to share the file, which makes
	 * things tougher.  As far as byte sexing goes, since the mpool region
	 * lives on a single host, there's no issue of that -- the entire
	 * region is byte sex dependent.  As far as variable sizes go, we make
	 * the simplifying assumption that 32-bit and 64-bit processes will
	 * get the same 32-bit values if we truncate any returned 64-bit value
	 * to a 32-bit value.
	 */
	tmp = (u_int32_t)fi.nFileIndexLow;
	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
		*fidp++ = *p++;
	tmp = (u_int32_t)fi.nFileIndexHigh;
	for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
		*fidp++ = *p++;

	if (unique_okay) {
		/*
		 * Use the system time to try to get a unique value
		 * within this process.  A millisecond counter
		 * overflows 32 bits in about 49 days.  So we use 8
		 * bytes, and don't bother with the volume ID, which
		 * is not very useful for our purposes.
		 */
		SYSTEMTIME st;

		GetSystemTime(&st);
		tmp = (st.wYear - 1900) * 12 + (st.wMonth - 1);
		for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
			*fidp++ = *p++;
		tmp = ((((st.wDay - 1) * 24 + st.wHour) * 60 +
			st.wMinute) * 60 + st.wSecond) * 1000 +
			st.wMilliseconds;
		for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
			*fidp++ = *p++;
		for (p = (u_int8_t *)&fid_serial, i = sizeof(u_int32_t);
		    i > 0; --i)
			*fidp++ = *p++;
	} else {
		tmp = (u_int32_t)fi.dwVolumeSerialNumber;
		for (p = (u_int8_t *)&tmp, i = sizeof(u_int32_t); i > 0; --i)
			*fidp++ = *p++;
	}

	return (0);
}
