mktemp.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
/* Copyright (c) 1988 AT&T */
/* All Rights Reserved */
/*
* mktemp() expects a string with up to six trailing 'X's.
* These will be overlaid with letters, digits and symbols from
* the portable filename character set. If every combination thus
* inserted leads to an existing file name, the string is shortened
* to length zero and a pointer to a null string is returned.
*
* The guarantee made by mktime() to the caller is that the
* generated file name string will not match the string
* produced by any other concurrent process using mktemp().
* To guarantee uniqueness across the process-id space,
* the process-id of the caller is encoded into the string.
* To allow repeated calls within the same process to generate
* different strings on each call, a sequence number is encoded
* into the string along with process-id.
*
* The encoding is performed using radix-64 (6 bits per character),
* with 64 characters taken from the portable file name character set.
* This allows the six X's to be a representation of a 36-bit integer
* composed of bit fields:
* ( pid | seq )
* where the process-id occupies the high-order bits and the sequence
* number occupies the low-order bits. The size of the pid field is
* not fixed at the traditional 15 bits (MAXPID = 30000); the system
* now allows a larger process-id space and MAXPID is obtained from
* the system with a call to sysconf(_SC_MAXPID).
*
* mktime() should fail if fewer than six X's are presented to it.
* However, this has been traditionally accepted and is preserved
* in the present code. The consequence is that the 36-bit integer
* is reduced to a (6*N)-bit integer, where N is the number of X's.
* mktime() fails immediately if the resulting integer is not large
* enough to contain MAXPID.
*
* In an attempt to confuse and thwart hackers, the starting
* sequence number is randomized using the current time.
*/
#define XCNT 6
#include "synonyms.h"
#include "mtlib.h"
#include <string.h>
#include <unistd.h>
#include <thread.h>
#include <synch.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
/*
* 64-bit digits, must be from the POSIX "portable file name character set".
*/
static char
chars[64] = {
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '_',
};
/*
* Find highest one bit set.
* Returns bit number of highest bit that is set.
* Low order bit is number 0, high order bit is number 31.
*/
static int
{
int h = 0;
if (i & 0xffff0000)
h += 16, i >>= 16;
if (i & 0xff00)
h += 8, i >>= 8;
if (i & 0xf0)
h += 4, i >>= 4;
if (i & 0xc)
h += 2, i >>= 2;
if (i & 0x2)
h += 1;
return (h);
}
char *
{
/* statics are protected by this static mutex */
static int pidshift = 0;
static int previous_try = 0;
static pid_t previous_pid = 0;
static int previous_xcnt = XCNT;
int try;
int tryshift;
int max_try;
char *s;
char *first_x;
int len;
return (as); /* a pointer to a null string is returned. */
/*
* Randomize the starting sequence number in
* an attempt to confuse and thwart hackers.
* Use the low 12 bits of the time in milliseconds.
*/
previous_pid = pid;
}
/* for all possible values of pid, 0 <= pid < (1 << pidshift) */
if (pidshift == 0) /* one-time initialization */
/* count the X's */
xcnt = 0;
xcnt++;
len--;
--s;
}
/* fail if we don't have enough X's to represent MAXPID */
/*
* Some broken programs call mktemp() repeatedly,
* passing the same string without reinserting the X's.
* Check to see if this is such a call by testing
* the trailing characters of the string for a
* match with the process-id.
*/
int c;
int i;
c = *--s;
for (i = 0; i < 64; i++)
if (c == chars[i])
break;
if (i == 64)
goto fail;
}
return (as);
}
goto fail;
}
/* we can try sequence numbers in the range 0 <= try < max_try */
if (previous_try >= max_try)
previous_try = 0;
try = previous_try;
for (;;) {
/* num is up to a 36-bit integer ... */
int i;
/* ... which we represent backwards in base 64 */
num >>= 6;
}
break; /* unrecoverable error */
/* remember where we left off for the next call */
return (as);
}
try = 0;
if (try == previous_try)
break;
}
fail:
*as = '\0';
return (as);
}