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lock.c
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C/C++ Source or Header
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1992-10-30
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11KB
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468 lines
/*
* lock.c -- deal with file locking on various architectures and UNIXs.
* dot_lock() creates a file with the same name as the parameter passed
* with the appendage ".lock" -- this is to be compatible with certain
* systems that don't use flock or lockf or whatever they have available
* that they don't use.
*/
#ifdef USG
#include <unistd.h>
#endif /* USG */
#include "mush.h"
#if defined(SYSV) && !defined(USG)
#include <sys/locking.h>
#endif /* SYSV && !USG */
#ifdef DOT_LOCK
#ifndef DOLOCK_PATH
#define DOLOCK_PATH "dotlock" /* Path to the executable */
#endif /* DOLOCK_PATH */
#ifndef DOLOCK_NAME
#define DOLOCK_NAME "dotlock" /* Name of the executable */
#endif /* DOLOCK_NAME */
#define DOLOCKIT "-l"
#define UNLOCKIT "-u"
#ifdef LOCK_PROG /* Define for standalone locking program */
/* System V Release 2 does not support saved-set-group-id, so it is not
* sufficient for mush to be setgid mail (or whatever group has write
* permission on /usr/mail). Instead, we need an external program that
* can be setgid, which mush then runs to create and remove lock files.
* Compiling this file with -DDOT_LOCK -DLOCK_PROG added to your CFLAGS
* will generate such a program:
*
* cc -o dotlock -DDOT_LOCK -DLOCK_PROG lock.c xcreat.c
*
* For mush purposes, you should hardwire the DOLOCK_PATH to the full path
* name of the installed executable. This helps prevent malicious users
* from substituting a different program.
*
* The program generated can also be used to perform mail locking from
* shell scripts, so you may wish to consider installing it (or a copy)
* in a publicly accessible location, e.g. /usr/local/bin. Note that
* this program is not compatible with Xenix mail locking!
*/
#undef on_intr()
#define on_intr() 0
#undef off_intr()
#define off_intr() 0
#undef print
#define print printf
#undef print_more
#define print_more fflush(stdout), printf
#undef error
#define error printf
#undef sprintf
/* Simple dotlock program. Exits 0 for success, nonzero for failure.
*
* Usage:
* dotlock -lock filename
* dotlock -unlock filename
*
* The options can be abbreviated to their first letter (-l or -u);
* any other usage fails silently.
*/
main(argc, argv)
int argc;
char **argv;
{
char *myname = rindex(argv[0], '/');
if (!myname)
myname = argv[0];
if (strcmp(myname, DOLOCK_NAME) != 0 || argc != 3)
exit(-1);
if (strncmp(argv[1], DOLOCKIT, 2) == 0)
dot_lock(argv[2]);
else if (strncmp(argv[1], UNLOCKIT, 2) == 0)
dot_unlock(argv[2]);
exit(-1);
}
#else /* !LOCK_PROG */
extern int sgid;
#ifdef BSD
extern int rgid;
#endif /* BSD */
#ifdef SVR2
/* No saved-setgid, so fork just long enough to create the lockfile. */
lock_proc(filename, how)
char *filename, *how;
{
int kid, pid, status;
errno = 0;
switch (kid = fork()) {
case 0:
execle(DOLOCK_PATH, DOLOCK_NAME, how, filename, NULL, environ);
return kid;
case -1:
error("Unable to fork to change group id");
return -1;
default:
/* For SYSV, we're not doing SIGCLD handling, so go ahead
* and reap everything in sight until we get the one we want.
*/
while ((pid = wait(&status)) != -1 && pid != kid)
;
if (pid == kid)
errno = ((status & 0xf) == 0) ? (status >> 8) & 0xf : 0
return errno ? -1 : 0;
}
}
#endif /* SVR2 */
#endif /* LOCK_PROG */
dot_lock(filename)
char *filename;
{
char buf[MAXPATHLEN];
int lockfd, cnt = 0;
SIGRET (*oldint)(), (*oldquit)();
#ifndef LOCK_PROG
#if defined(SYSV) && !defined(HPUX) && !defined(IRIX4)
/* Only the spoolfile needs to be dot_locked -- other files are
* handled by lock_fopen, below. To avoid collisions with 14-char
* file name limits, we allow dot_locking ONLY of the spoolfile.
*/
if (strcmp(spoolfile, filename) != 0)
return 0;
#ifdef SVR2
return lock_proc(filename, DOLOCKIT);
#endif /* SVR2 */
#endif /* SYSV && !HPUX && !IRIX4 */
#ifdef BSD
setregid(rgid, sgid);
#else /* BSD */
setgid(sgid);
#endif /* BSD */
#endif /* !LOCK_PROG */
#ifdef M_XENIX
(void) sprintf(buf, "/tmp/%.10s.mlk", login);
#else /* M_XENIX */
(void) sprintf(buf, "%s.lock", filename);
#endif /* M_XENIX */
on_intr();
while ((lockfd = xcreat(buf, 0444)) == -1) {
if (errno != EEXIST) {
error("unable to lock %s", filename);
break;
}
if (cnt++ == 0)
print("%s already locked, waiting", filename);
else
print_more(".");
sleep(1);
if (ison(glob_flags, WAS_INTR)) {
print_more("\nAborted.\n");
break;
}
}
off_intr();
if (lockfd != -1) {
if (cnt)
print("done.\n");
(void) close(lockfd);
}
#ifdef LOCK_PROG
if (lockfd < 0)
print_more("\n");
exit(lockfd < 0? errno : 0);
#else /* !LOCK_PROG */
#ifdef BSD
setregid(sgid, rgid);
#else
setgid(getgid());
#endif /* BSD */
return lockfd == -1? -1 : 0;
#endif /* LOCK_PROG */
}
dot_unlock(filename)
char *filename;
{
char buf[MAXPATHLEN], *p;
#if !defined(M_XENIX) || defined(LOCK_PROG)
(void) sprintf(buf, "%s.lock", filename);
#ifndef LOCK_PROG
{
/* If the file was locked through open_file(), we may not have
* a complete pathname to work with here. Expand it and test
* whether we need to unlink at all. This should really be
* handled by having open_file() return the name it used, but
* that breaks too many other things at the moment.
*/
int isdir = 0;
p = getpath(buf, &isdir);
if (isdir)
return 0;
(void) strcpy(buf, p);
}
#if defined(SYSV) && !defined(HPUX) && !defined(IRIX4)
if (strncmp(spoolfile, buf, strlen(spoolfile)) != 0)
return 0;
#ifdef SVR2
p = rindex(buf, '.');
*p = 0;
return lock_proc(buf, UNLOCKIT);
#endif /* SVR2 */
#endif /* SYSV && !HPUX && !IRIX4 */
#else /* LOCK_PROG */
errno = 0;
#endif /* !LOCK_PROG */
#else /* M_XENIX && !LOCK_PROG */
(void) sprintf(buf, "/tmp/%.10s.mlk", login);
#endif /* !M_XENIX || LOCK_PROG */
#ifndef LOCK_PROG
#ifdef BSD
setregid(rgid, sgid);
#else /* BSD */
setgid(sgid);
#endif /* BSD */
#endif /* !LOCK_PROG */
(void) unlink(buf);
#ifdef LOCK_PROG
exit(errno);
#else /* !LOCK_PROG */
#ifdef BSD
setregid(sgid, rgid);
#else
setgid(getgid());
#endif /* BSD */
#endif /* LOCK_PROG */
return 0;
}
#endif /* DOT_LOCK */
#ifndef LOCK_PROG
#ifdef SYSV
/*
* Define some BSD names for the SYSV world
*/
#ifdef USG
#define LOCK_SH F_RDLCK
#define LOCK_EX F_WRLCK
#define LOCK_UN F_UNLCK
#else /* USG */
#define LOCK_SH LK_LOCK
#define LOCK_EX LK_LOCK
#define LOCK_UN LK_UNLCK
#endif /* USG */
#define LOCK_NB 0 /* Always non-blocking in this case */
#ifdef EWOULDBLOCK
#undef EWOULDBLOCK
#endif /* EWOULDBLOCK */
#define EWOULDBLOCK EAGAIN
#ifndef F_SETLKW
#define F_SETLKW F_SETLK
#endif /* F_SETLKW */
flock(fd, op)
int fd, op;
{
#ifndef USG
(void) locking(fd, op, 0); /* old xenix (sys III) */
return 0;
#else
struct flock l;
l.l_len = 0L;
l.l_start = 0L;
l.l_whence = 1;
l.l_type = op;
return fcntl(fd, F_SETLKW, &l);
#endif /* USG */
}
#endif /* SYSV */
static struct options *exclude_list;
/* Quick'n'dirty test to avoid opening the same file multiple times.
* Fails if we aren't passed full paths or if the file is known by
* more than one name, but you can't have everything.
*/
static FILE *
exclusive_fopen(filename, mode)
char *filename, *mode;
{
struct options *tmp;
FILE *fp;
for (tmp = exclude_list; tmp; tmp = tmp->next)
if (strcmp(tmp->option, filename) == 0) {
errno = EWOULDBLOCK;
return NULL_FILE;
}
#ifdef DOT_LOCK
/* For additional assurance that each file is opened only once,
* and for ease of recovery from interrupts and errors, do the
* dot-locking here and unlock in exclusive_fclose().
*/
if (dot_lock(filename) != 0)
return NULL_FILE;
#endif /* DOT_LOCK */
if (!(fp = mask_fopen(filename, mode)))
return NULL_FILE;
if (tmp = (struct options *)malloc(sizeof(struct options))) {
tmp->option = savestr(filename);
tmp->value = (char *)fp;
/*
* NOTE: The LCKDFLDIR code below depends on this stackwise
* insertion to be able to close/reopen the file pointer.
* These routines therefore cannot cleanly be used outside
* of lock_fopen() and close_lock(), which handle LCKDFLDIR.
*/
tmp->next = exclude_list;
exclude_list = tmp;
return fp;
} else
(void) fclose(fp);
return NULL_FILE;
}
static int
exclusive_fclose(fileptr)
FILE *fileptr;
{
struct options *tmp1, *tmp2;
int n = 0;
for (tmp1 = tmp2 = exclude_list; tmp1; tmp2 = tmp1, tmp1 = tmp1->next)
if ((FILE *)(tmp1->value) == fileptr) {
if (tmp1 == tmp2)
exclude_list = tmp1->next;
else
tmp2->next = tmp1->next;
#ifdef DOT_LOCK
dot_unlock(tmp1->option);
#endif /* DOT_LOCK */
xfree(tmp1->option);
#ifndef LCKDFLDIR
/* LCKDFLDIR needs lk_fclose(), so let caller do it */
n = fclose(fileptr);
#endif /* !LCKDFLDIR */
xfree(tmp1);
break;
}
return n;
}
FILE *
lock_fopen(filename, mode)
char *filename;
char *mode;
{
FILE *mail_fp = NULL_FILE;
struct options exclude;
int fd, lk;
int cnt = 0;
SIGRET (*oldint)(), (*oldquit)();
#ifdef LCKDFLDIR
extern FILE *lk_fopen();
#endif /* !LCKDFLDIR */
if (debug && do_set(set_options, "deadlock")) {
(void) un_set(&set_options, "deadlock");
return NULL_FILE;
}
if (!(mail_fp = exclusive_fopen(filename, mode)))
return NULL_FILE;
fd = fileno(mail_fp);
if (mode[0] != 'r' || mode[1] == '+')
lk = LOCK_EX | LOCK_NB;
else
lk = LOCK_SH | LOCK_NB;
on_intr();
#ifdef LCKDFLDIR
(void) fclose(mail_fp);
while (isoff(glob_flags, WAS_INTR))
if (mail_fp = lk_fopen(filename, mode, NULL, NULL, 0)) {
/* See note in exclusive_fopen() above */
exclude_list->value = (char *)mail_fp;
break;
} else /* uses the open brace below the #endif LCKDFLDIR */
#else /* !LCKDFLDIR */
while (isoff(glob_flags, WAS_INTR) && flock(fd, lk))
#endif /* LCKDFLDIR */
{
#ifdef LCKDFLDIR
if (Access(filename, any(mode, "aw+") ? W_OK : R_OK) == 0)
#else /* !LCKDFLDIR */
if (errno == EWOULDBLOCK
#ifdef M_UNIX
|| errno == EACCES
#endif /* M_UNIX */
)
#endif /* LCKDFLDIR */
{
if (isoff(glob_flags, REDIRECT))
if (!cnt++)
print("\nwaiting to lock");
else
print(".");
} else {
error("Unable to lock \"%s\"", filename);
(void) exclusive_fclose(mail_fp);
off_intr();
return NULL_FILE;
}
(void) fflush(stdout);
sleep(1);
}
if (cnt)
print("\n");
cnt = (ison(glob_flags, WAS_INTR) != 0);
off_intr();
if (cnt) {
(void) exclusive_fclose(mail_fp);
return NULL_FILE;
}
return mail_fp;
}
/*ARGSUSED*/
close_lock(filename, fp)
char *filename;
FILE *fp;
{
#ifdef LCKDFLDIR
(void) exclusive_fclose(fp); /* Only removes the list elem */
return lk_fclose(fp, filename, NULL, NULL);
#else /* !LCKDFLDIR */
fflush(fp);
(void) flock(fileno(fp), LOCK_UN);
return exclusive_fclose(fp);
#endif /* LCKDFLDIR */
}
/* Make sure we don't leave dead lockfiles lying around */
void
droplocks()
{
while (exclude_list)
close_lock(exclude_list->option, (FILE *)exclude_list->value);
}
#endif /* LOCK_PROG */