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/*
* lockfile.c Safely creates a lockfile, also over NFS.
* This file also holds the implementation for
* the Svr4 maillock functions.
*
* Version: @(#)lockfile.c 1.0 05-Jun-1999 miquels@cistron.nl
*
* Copyright (C) Miquel van Smoorenburg 1997,1998,1999.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*/
#include "autoconf.h"
#include <sys/types.h>
#if HAVE_SYS_PARAM_H
#include <sys/param.h>
#endif
#include <sys/stat.h>
#include <sys/wait.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <errno.h>
#include <lockfile.h>
#include <maillock.h>
#ifdef HAVE_UTIME
#include <utime.h>
#endif
#ifdef LIB
static char mlockfile[MAXPATHLEN];
static int islocked = 0;
#endif
#ifndef LIB
extern int check_sleep(int);
#endif
#if !defined(LIB) || defined(MAILGROUP)
/*
* See if we can write to the directory.
* Returns: -1 fail
* 0 OK writable
*/
#ifdef LIB
static
#endif
int eaccess(char *fn, gid_t gid, struct stat *st)
{
struct stat tmp;
uid_t uid = geteuid();
if (st == NULL) st = &tmp;
if (stat(fn, st) != 0)
return -1;
errno = EPERM;
if (uid == 0) return 0;
if (st->st_uid == uid)
return (st->st_mode & 0200) ? 0 : -1;
if (st->st_gid == gid)
return (st->st_mode & 0020) ? 0 : -1;
return (st->st_mode & 0002) ? 0 : -1;
}
#endif
#if defined(LIB) && defined(MAILGROUP)
/*
* Can we write to the directory of the lockfile ?
*/
static int need_extern(const char *file)
{
gid_t egid = getegid();
struct stat st;
static gid_t mailgid = -1;
char dir[MAXPATHLEN];
char *p;
/*
* Find directory.
*/
strcpy(dir, file);
if ((p = strrchr(dir, '/')) != NULL)
*p = 0;
else
strcpy(dir, ".");
if (eaccess(dir, egid, NULL) >= 0)
return 0;
/*
* See if accessible for group mail. We find out what
* "group mail" is by statting LOCKPROG, that saves us
* from having to call getgrgid() in a library.
*/
if (mailgid == (gid_t)-1) {
if (stat(LOCKPROG, &st) < 0 || !(st.st_mode & S_ISGID))
return 0;
mailgid = st.st_gid;
}
return (eaccess(dir, mailgid, NULL) >= 0);
}
/*
* Call external program to do the actual locking.
*/
static int do_extern(char *opt, const char *lockfile, int retries, int flags)
{
sigset_t set, oldset;
char buf[4];
pid_t pid, n;
int st;
/*
* Block SIGCHLD. The main program might have installed
* handlers we don't want to call.
*/
sigemptyset(&set);
sigaddset(&set, SIGCHLD);
sigprocmask(SIG_BLOCK, &set, &oldset);
/*
* Fork, execute locking program and wait.
*/
if ((pid = fork()) < 0)
return L_ERROR;
if (pid == 0) {
sprintf(buf, "%d", retries % 1000);
execl(LOCKPROG, LOCKPROG, opt, "-r", buf, "-q",
(flags & L_PID) ? "-p" : "-N", lockfile, NULL);
_exit(L_ERROR);
}
/*
* Wait for return status - do something appropriate
* if program died or returned L_ERROR.
*/
while ((n = waitpid(pid, &st, 0)) != pid)
if (n < 0 && errno != EINTR)
break;
if (!sigismember(&oldset, SIGCHLD))
sigprocmask(SIG_UNBLOCK, &set, NULL);
if (n < 0)
return L_ERROR;
if (!WIFEXITED(st) || WEXITSTATUS(st) == L_ERROR) {
errno = EINTR;
return L_ERROR;
}
return WEXITSTATUS(st);
}
#endif
/*
* Create a lockfile.
*/
int lockfile_create(const char *lockfile, int retries, int flags)
{
struct stat st, st1;
char tmplock[MAXPATHLEN];
char sysname[256];
char buf[8];
char *p;
int sleeptime = 5;
int statfailed = 0;
int fd;
int i, e, len;
/*
* Safety measure.
*/
if (strlen(lockfile) + 32 > MAXPATHLEN) {
errno = ENAMETOOLONG;
return L_ERROR;
}
#if defined(LIB) && defined(MAILGROUP)
if (need_extern(lockfile))
return do_extern("-l", lockfile, retries, flags);
#endif
/*
* Create a temp lockfile (hopefully unique) and write
* either our pid/ppid in it, or 0\0 for svr4 compatibility.
*/
if (gethostname(sysname, sizeof(sysname)) < 0)
return L_ERROR;
if ((p = strchr(sysname, '.')) != NULL)
*p = 0;
strcpy(tmplock, lockfile);
if ((p = strrchr(tmplock, '/')) == NULL)
p = tmplock;
else
p++;
sprintf(p, ".lk%05d%x%s",
(int)getpid(), (int)time(NULL) & 15, sysname);
i = umask(022);
fd = open(tmplock, O_WRONLY|O_CREAT|O_EXCL, 0644);
e = errno;
umask(i);
if (fd < 0) {
errno = e;
return L_TMPLOCK;
}
if (flags & (L_PID | L_PPID)) {
sprintf(buf, "%d\n",
(flags & L_PID) ? (int)getpid() : (int)getppid());
p = buf;
len = strlen(buf);
} else {
p = "0";
len = 2;
}
i = write(fd, p, len);
e = errno;
if (close(fd) != 0) {
e = errno;
i = -1;
}
if (i != len) {
unlink(tmplock);
errno = i < 0 ? e : EAGAIN;
return L_TMPWRITE;
}
/*
* Now try to link the temporary lock to the lock.
*/
for (i = 0; i < retries && retries > 0; i++) {
sleeptime = i > 12 ? 60 : 5 * i;
if (sleeptime > 0)
#ifdef LIB
sleep(sleeptime);
#else
if ((e = check_sleep(sleeptime)) != 0) {
unlink(tmplock);
return e;
}
#endif
/*
* Now lock by linking the tempfile to the lock.
*
* KLUDGE: some people say the return code of
* link() over NFS can't be trusted.
* EXTRA FIX: the value of the nlink field
* can't be trusted (may be cached).
*/
(void)link(tmplock, lockfile);
if (lstat(tmplock, &st1) < 0)
return L_ERROR; /* Can't happen */
if (lstat(lockfile, &st) < 0) {
if (statfailed++ > 5) {
/*
* Normally, this can't happen; either
* another process holds the lockfile or
* we do. So if this error pops up
* repeatedly, just exit...
*/
e = errno;
(void)unlink(tmplock);
errno = e;
return L_MAXTRYS;
}
continue;
}
/*
* See if we got the lock.
*/
if (st.st_rdev == st1.st_rdev &&
st.st_ino == st1.st_ino) {
(void)unlink(tmplock);
return L_SUCCESS;
}
statfailed = 0;
/*
* If there is a lockfile and it is invalid,
* remove the lockfile.
*/
if (lockfile_check(lockfile, flags) == -1)
unlink(lockfile);
}
(void)unlink(tmplock);
errno = EAGAIN;
return L_MAXTRYS;
}
/*
* See if a valid lockfile is present.
* Returns 0 if so, -1 if not.
*/
int lockfile_check(const char *lockfile, int flags)
{
struct stat st;
char buf[16];
time_t now;
pid_t pid;
int fd, len, r;
if (stat(lockfile, &st) < 0)
return -1;
/*
* Get the contents and mtime of the lockfile.
* Use the time of the file system.
*/
time(&now);
pid = 0;
if ((fd = open(lockfile, O_RDONLY)) >= 0) {
if ((len = read(fd, buf, sizeof(buf))) >= 0 &&
fstat(fd, &st) == 0)
now = st.st_atime;
close(fd);
if (len > 0 && (flags & (L_PID|L_PPID))) {
buf[len] = 0;
pid = atoi(buf);
}
}
if (pid > 0) {
/*
* If we have a pid, see if the process
* owning the lockfile is still alive.
*/
r = kill(pid, 0);
if (r == 0 || errno == EPERM)
return 0;
if (r < 0 && errno == ESRCH)
return -1;
/* EINVAL - FALLTHRU */
}
/*
* Without a pid in the lockfile, the lock
* is valid if it is newer than 5 mins.
*/
if (now < st.st_mtime + 300)
return 0;
return -1;
}
/*
* Remove a lock.
*/
int lockfile_remove(const char *lockfile)
{
#if defined(LIB) && defined(MAILGROUP)
if (need_extern(lockfile))
return do_extern("-u", lockfile, 0, 0);
#endif
return (unlink(lockfile) < 0 && errno != ENOENT) ? -1 : 0;
}
/*
* Touch a lock.
*/
int lockfile_touch(const char *lockfile)
{
#ifdef HAVE_UTIME
return utime(lockfile, NULL);
#else
return utimes(lockfile, NULL);
#endif
}
#ifdef LIB
/*
* Lock a mailfile. This looks a lot like the SVR4 function.
* Arguments: lusername, retries.
*/
int maillock(const char *name, int retries)
{
char *p, *mail;
int i;
if (islocked) return 0;
if (strlen(name) + sizeof(MAILDIR) + 6 > MAXPATHLEN) {
errno = ENAMETOOLONG;
return L_NAMELEN;
}
/*
* If $MAIL is for the same username as "name"
* then use $MAIL instead.
*/
sprintf(mlockfile, "%s%s.lock", MAILDIR, name);
if ((mail = getenv("MAIL")) != NULL) {
if ((p = strrchr(mail, '/')) != NULL)
p++;
else
p = mail;
if (strcmp(p, name) == 0) {
if (strlen(mail) + 6 > MAXPATHLEN) {
errno = ENAMETOOLONG;
return L_NAMELEN;
}
sprintf(mlockfile, "%s.lock", mail);
}
}
i = lockfile_create(mlockfile, retries, 0);
if (i == 0) islocked = 1;
return i;
}
void mailunlock(void)
{
if (!islocked) return;
lockfile_remove(mlockfile);
islocked = 0;
}
void touchlock(void)
{
lockfile_touch(mlockfile);
}
#endif
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