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/**
* \file lock.c cross-platform concurrency locking for fetchmail
*
* For license terms, see the file COPYING in this directory.
*/
#include "config.h"
#include "fetchmail.h"
#include <stdio.h>
#ifdef HAVE_STRING_H
#include <string.h> /* strcat() */
#endif
#if defined(STDC_HEADERS)
#include <stdlib.h>
#endif
#if defined(HAVE_UNISTD_H)
#include <unistd.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include "i18n.h"
#include "lock.h"
static char *lockfile; /** name of lockfile */
static int lock_acquired; /** flag if have we acquired a lock */
void fm_lock_setup(struct runctl *ctl)
/* set up the global lockfile name */
{
/* set up to do lock protocol */
const char *const FETCHMAIL_PIDFILE="fetchmail.pid";
/* command-line option override */
if (ctl->pidfile) {
lockfile = xstrdup(ctl->pidfile);
return;
}
/* defaults */
if (getuid() == ROOT_UID) {
lockfile = (char *)xmalloc(strlen(PID_DIR)
+ strlen(FETCHMAIL_PIDFILE) + 2); /* 2: "/" and NUL */
strcpy(lockfile, PID_DIR);
strcat(lockfile, "/");
strcat(lockfile, FETCHMAIL_PIDFILE);
} else {
lockfile = (char *)xmalloc(strlen(fmhome)
+ strlen(FETCHMAIL_PIDFILE) + 3); /* 3: "/", "." and NUL */
strcpy(lockfile, fmhome);
strcat(lockfile, "/");
if (at_home)
strcat(lockfile, ".");
strcat(lockfile, FETCHMAIL_PIDFILE);
}
}
static void unlockit(void)
/* must-do actions for exit (but we can't count on being able to do malloc) */
{
if (lockfile && lock_acquired)
unlink(lockfile) && truncate(lockfile, (off_t)0);
}
void fm_lock_dispose(void)
/* arrange for a lock to be removed on process exit */
{
#ifdef HAVE_ATEXIT
atexit(unlockit);
#endif
}
int fm_lock_state(void)
{
long pid;
int st;
FILE *lockfp;
int bkgd = FALSE;
if ((lockfp = fopen(lockfile, "r")) != NULL)
{
int args = fscanf(lockfp, "%ld %d", &pid, &st);
bkgd = (args == 2);
if (ferror(lockfp)) {
report(stderr, GT_("fetchmail: error reading lockfile \"%s\": %s\n"),
lockfile, strerror(errno));
fclose(lockfp); /* not checking should be safe, file mode was "r" */
exit(PS_EXCLUDE);
}
fclose(lockfp); /* not checking should be safe, file mode was "r" */
if (args == EOF || args == 0 || kill(pid, 0) == -1) {
/* ^ could not read PID || process does not exist */
/* => lockfile is stale, unlink it */
pid = 0;
report(stderr,GT_("fetchmail: removing stale lockfile \"%s\"\n"), lockfile);
if (unlink(lockfile)) {
if (errno != ENOENT) {
if (outlevel >= O_VERBOSE) {
report(stderr, GT_("fetchmail: cannot unlink lockfile \"%s\" (%s), trying to write to it\n"),
lockfile, strerror(errno));
}
/* we complain but we don't exit; it might be
* writable for us, but in a directory we cannot
* write to. This means we can write the new PID to
* the file. Truncate to be safe in case the PID is
* recycled by another process later.
* \bug we should use fcntl() style locks or
* something else instead in a future release. */
if (truncate(lockfile, (off_t)0)) {
/* but if we cannot truncate the file either,
* assume that we cannot write to it later,
* complain and quit. */
report(stderr, GT_("fetchmail: cannot write to lockfile \"%s\" either (%s), exiting\n"),
strerror(errno), lockfile);
exit(PS_EXCLUDE);
}
}
}
}
} else {
pid = 0;
if (errno != ENOENT) {
report(stderr, GT_("fetchmail: error opening lockfile \"%s\": %s\n"),
lockfile, strerror(errno));
exit(PS_EXCLUDE);
}
}
return(bkgd ? -pid : pid);
}
void fm_lock_assert(void)
/* assert that we already possess a lock */
{
lock_acquired = TRUE;
}
void fm_lock_or_die(void)
/* get a lock on a given host or exit */
{
int fd;
char tmpbuf[50];
if (!lock_acquired) {
int e = 0;
fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, 0666);
if (fd == -1 && EEXIST == errno) {
fd = open(lockfile, O_WRONLY|O_TRUNC, 0666);
}
if (-1 != fd) {
ssize_t wr;
snprintf(tmpbuf, sizeof(tmpbuf), "%ld\n", (long)getpid());
wr = write(fd, tmpbuf, strlen(tmpbuf));
if (wr == -1 || (size_t)wr != strlen(tmpbuf))
e = 1;
if (run.poll_interval)
{
snprintf(tmpbuf, sizeof(tmpbuf), "%d\n", run.poll_interval);
wr = write(fd, tmpbuf, strlen(tmpbuf));
if (wr == -1 || (size_t)wr != strlen(tmpbuf))
e = 1;
}
if (fsync(fd)) e = 1;
if (close(fd)) e = 1;
} else {
e = 1;
}
if (e == 0) {
lock_acquired = TRUE;
} else {
report(stderr, GT_("fetchmail: lock creation failed, pidfile \"%s\": %s\n"), lockfile, strerror(errno));
exit(PS_EXCLUDE);
}
}
}
void fm_lock_release(void)
/* release a lock on a given host */
{
if (unlink(lockfile)) {
if (truncate(lockfile, (off_t)0)) {
report(stderr, GT_("fetchmail: cannot remove or truncate pidfile \"%s\": %s\n"), strerror(errno));
}
}
}
/* lock.c ends here */
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