NetBSD/usr.bin/shlock/shlock.c

421 lines
10 KiB
C

/* $NetBSD: shlock.c,v 1.15 2021/04/17 00:02:19 christos Exp $ */
/*-
* Copyright (c) 2006 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Erik E. Fair.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
** Program to produce reliable locks for shell scripts.
** Algorithm suggested by Peter Honeyman, January 1984,
** in connection with HoneyDanBer UUCP.
**
** I tried extending this to handle shared locks in November 1987,
** and ran into to some fundamental problems:
**
** Neither 4.3 BSD nor System V have an open(2) with locking,
** so that you can open a file and have it locked as soon as
** it's real; you have to make two system calls, and there's
** a race...
**
** When removing dead process id's from a list in a file,
** you need to truncate the file (you don't want to create a
** new one; see above); unfortunately for the portability of
** this program, only 4.3 BSD has ftruncate(2).
**
** Erik E. Fair <fair@ucbarpa.berkeley.edu>, November 8, 1987
**
** Extensions for UUCP style locks (i.e. pid is an int in the file,
** rather than an ASCII string). Also fix long standing bug with
** full file systems and temporary files.
**
** Erik E. Fair <fair@apple.com>, November 12, 1989
**
** ANSIfy the code somewhat to make gcc -Wall happy with the code.
** Submit to NetBSD
**
** Erik E. Fair <fair@clock.org>, May 20, 1997
*/
#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: shlock.c,v 1.15 2021/04/17 00:02:19 christos Exp $");
#endif
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <err.h>
#include <fcntl.h> /* Needed on hpux */
#include <stdio.h>
#include <signal.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#define LOCK_SET 0
#define LOCK_FAIL 1
#define LOCK_GOOD 0
#define LOCK_BAD 1
#define FAIL (-1)
#define TRUE 1
#define FALSE 0
static int Debug = FALSE;
static char *Pname;
static const char USAGE[] = "%s: USAGE: %s [-du] [-p PID] -f file\n";
static const char E_unlk[] = "unlink(%s)";
static const char E_link[] = "link(%s, %s)";
static const char E_open[] = "open(%s)";
static const char E_stat[] = "stat(%s)";
#define dprintf if (Debug) printf
/*
** Prototypes to make the ANSI compilers happy
** Didn't lint used to do type and argument checking?
** (and wasn't that sufficient?)
*/
/* the following is in case you need to make the prototypes go away. */
static char *xtmpfile(const char *, pid_t, int);
static int p_exists(pid_t);
static int cklock(const char *, struct stat *, int);
static int mklock(const char *, pid_t, int);
__dead static void bad_usage(void);
/*
** Create a temporary file, all ready to lock with.
** The file arg is so we get the filename right, if he
** gave us a full path, instead of using the current directory
** which might not be in the same filesystem.
*/
static char *
xtmpfile(const char *file, pid_t pid, int uucpstyle)
{
int fd;
size_t len;
char *cp, buf[BUFSIZ];
static char tempname[BUFSIZ];
snprintf(buf, sizeof(buf), "shlock%jd", (intmax_t)getpid());
if ((cp = strrchr(strcpy(tempname, file), '/')) != NULL) {
*++cp = '\0';
(void) strcat(tempname, buf);
} else
(void) strcpy(tempname, buf);
dprintf("%s: temporary filename: %s\n", Pname, tempname);
snprintf(buf, sizeof(buf), "%jd\n", (intmax_t)pid);
len = strlen(buf);
while ((fd = open(tempname, O_RDWR|O_CREAT|O_TRUNC|O_SYNC|O_EXCL, 0644))
== -1)
{
switch(errno) {
case EEXIST:
if (unlink(tempname) == -1) {
warn(E_unlk, tempname);
return NULL;
}
break;
default:
warn(E_open, tempname);
return NULL;
}
}
/*
** Write the PID into the temporary file before attempting to link
** to the actual lock file. That way we have a valid lock the instant
** the link succeeds.
*/
if (uucpstyle ?
(write(fd, &pid, sizeof(pid)) != sizeof(pid)) :
(write(fd, buf, len) != (ssize_t)len))
{
warn("write(%s,%jd)", tempname, (intmax_t)pid);
(void) close(fd);
if (unlink(tempname) == -1) {
warn(E_unlk, tempname);
}
return NULL;
}
(void) close(fd);
return tempname;
}
/*
** Does the PID exist?
** Send null signal to find out.
*/
static int
p_exists(pid_t pid)
{
dprintf("%s: process %jd is ", Pname, (intmax_t)pid);
if (pid <= 0) {
dprintf("invalid\n");
return FALSE;
}
if (kill(pid, 0) == -1) {
switch(errno) {
case ESRCH:
dprintf("dead %jd\n", (intmax_t)pid);
return FALSE; /* pid does not exist */
case EPERM:
dprintf("alive\n");
return TRUE; /* pid exists */
default:
dprintf("state unknown: %s\n", strerror(errno));
return TRUE; /* be conservative */
}
}
dprintf("alive\n");
return TRUE; /* pid exists */
}
/*
** Check the validity of an existing lock file.
**
** Read the PID out of the lock
** Send a null signal to determine whether that PID still exists
** Existence (or not) determines the validity of the lock.
**
** Two bigs wins to this algorithm:
**
** o Locks do not survive crashes of either the system or the
** application by any appreciable period of time.
**
** o No clean up to do if the system or application crashes.
**
*/
static int
cklock(const char *file, struct stat *st, int uucpstyle)
{
int fd = open(file, O_RDONLY);
ssize_t len;
pid_t pid;
char buf[BUFSIZ];
dprintf("%s: checking extant lock <%s>\n", Pname, file);
if (fd == -1) {
if (errno != ENOENT)
warn(E_open, file);
return TRUE; /* might or might not; conservatism */
}
if (st != NULL && fstat(fd, st) == -1) {
warn(E_stat, file);
close(fd);
return TRUE;
}
if (uucpstyle ?
((len = read(fd, &pid, sizeof(pid))) != sizeof(pid)) :
((len = read(fd, buf, sizeof(buf))) <= 0))
{
close(fd);
dprintf("%s: lock file format error\n", Pname);
return FALSE;
}
close(fd);
buf[len + 1] = '\0';
return p_exists(uucpstyle ? pid : atoi(buf));
}
static int
mklock(const char *file, pid_t pid, int uucpstyle)
{
char *tmp, tmp2[BUFSIZ + 2];
int retcode = FALSE;
struct stat stlock, sttmp, stlock2;
dprintf("%s: trying lock <%s> for process %jd\n", Pname, file,
(intmax_t)pid);
if ((tmp = xtmpfile(file, pid, uucpstyle)) == NULL)
return FALSE;
while (link(tmp, file) == -1) {
switch(errno) {
case EEXIST:
dprintf("%s: lock <%s> already exists\n", Pname, file);
if (cklock(file, &stlock, uucpstyle)) {
dprintf("%s: extant lock is valid\n", Pname);
goto out;
}
if (stat(tmp, &sttmp) == -1) {
warn(E_stat, tmp);
goto out;
}
/*
* We need to take another lock against the lock
* file to protect it against multiple removals
*/
snprintf(tmp2, sizeof(tmp2), "%s-2", tmp);
if (unlink(tmp2) == -1 && errno != ENOENT) {
warn(E_unlk, tmp2);
goto out;
}
if (stlock.st_ctime >= sttmp.st_ctime) {
dprintf("%s: lock time changed %jd >= %jd\n",
Pname, (intmax_t)stlock.st_ctime,
(intmax_t)stlock2.st_ctime);
goto out;
}
if (stlock.st_nlink != 1) {
dprintf("%s: someone else linked to it %d\n",
Pname, stlock.st_nlink);
goto out;
}
if (link(file, tmp2) == -1) {
/* someone took our temp name! */
warn(E_link, file, tmp2);
goto out2;
}
if (stat(file, &stlock2) == -1) {
warn(E_stat, file);
goto out2;
}
if (stlock.st_ino != stlock2.st_ino) {
dprintf("%s: lock inode changed %jd != %jd\n",
Pname, (intmax_t)stlock.st_ino,
(intmax_t)stlock2.st_ino);
goto out2;
}
if (stlock2.st_nlink != 2) {
dprintf("%s: someone else linked to it %d\n",
Pname, stlock2.st_nlink);
goto out2;
}
dprintf("%s: lock is invalid, removing\n", Pname);
if (unlink(file) == -1) {
warn(E_unlk, file);
goto out2;
}
if (unlink(tmp2) == -1)
goto out2;
break;
default:
warn(E_link, tmp, file);
goto out;
}
}
if (stat(tmp, &sttmp) == -1) {
warn(E_stat, tmp);
goto out;
}
if (sttmp.st_nlink == 2) {
dprintf("%s: got lock <%s>\n", Pname, file);
retcode = TRUE;
goto out;
}
out2:
if (unlink(tmp2) == -1) {
warn(E_unlk, tmp2);
}
out:
if (unlink(tmp) == -1) {
warn(E_unlk, tmp);
}
return retcode;
}
static void
bad_usage(void)
{
fprintf(stderr, USAGE, Pname, Pname);
exit(LOCK_FAIL);
}
int
main(int ac, char **av)
{
int x;
char *file = NULL;
pid_t pid = 0;
int uucpstyle = FALSE; /* indicating UUCP style locks */
int only_check = TRUE; /* don't make a lock */
Pname = ((Pname = strrchr(av[0], '/')) ? Pname + 1 : av[0]);
for(x = 1; x < ac; x++) {
if (av[x][0] == '-') {
switch(av[x][1]) {
case 'u':
uucpstyle = TRUE;
break;
case 'd':
Debug = TRUE;
break;
case 'p':
if (strlen(av[x]) > 2) {
pid = atoi(&av[x][2]);
} else {
if (++x >= ac) {
bad_usage();
}
pid = atoi(av[x]);
}
only_check = FALSE; /* wants one */
break;
case 'f':
if (strlen(av[x]) > 2) {
file = &av[x][2];
} else {
if (++x >= ac) {
bad_usage();
}
file = av[x];
}
break;
default:
bad_usage();
}
}
}
if (file == NULL || (!only_check && pid <= 0)) {
bad_usage();
}
if (only_check) {
exit(cklock(file, NULL, uucpstyle) ? LOCK_GOOD : LOCK_BAD);
}
exit(mklock(file, pid, uucpstyle) ? LOCK_SET : LOCK_FAIL);
}