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#include <unistd.h>
#include <sys/stat.h>
#include <stdio.h>
#include <limits.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>
#include <pwd.h>
#include <libdaemon/dlog.h>
#include "lock.h"
#include "util.h"
#include "main.h"
/* Where do lockfiles reside? */
#define LOCK_PATH "/var/lock"
static const char *lockfile(const char *dev) {
static char lockfile[PATH_MAX];
snprintf(lockfile, sizeof(lockfile), "%s/LCK..%s", LOCK_PATH, basename((char*) dev));
return lockfile;
}
static const char *tempfile(const char *path) {
static char t[PATH_MAX];
snprintf(t, sizeof(t), "%s.tmp.%lu", path, (unsigned long) getpid());
return t;
}
int device_lock(const char *dev) {
struct stat st;
int fd;
const char *path, *temp;
char buf[100];
char uidbuf[32];
if (stat(LOCK_PATH, &st) != 0 || !S_ISDIR(st.st_mode)) {
daemon_log(LOG_ERR, "Failed to lock device, directory "LOCK_PATH" not existent.");
return -1;
}
path = lockfile(dev);
temp = tempfile(path);
for (;;) {
mode_t u;
struct passwd* pw;
char *username;
if ((fd = open(path, O_RDONLY)) < 0) {
if (errno != ENOENT) {
daemon_log(LOG_ERR, "Failed to open lock file: %s", strerror(errno));
return -1;
}
}
if (fd >= 0) {
ssize_t n;
n = loop_read(fd, buf, sizeof(buf) - 1);
close(fd);
if (n < 0) {
close(fd);
daemon_log(LOG_ERR, "Failed to read from lock file: %s", strerror(errno));
return -1;
}
if (n > 0) {
pid_t pid;
if (n == 4)
pid = (pid_t) *((uint32_t*) buf);
else {
unsigned long v;
buf[n] = 0;
sscanf(buf, "%lu", &v);
pid = (pid_t) v;
}
if (pid > 0) {
if (kill(pid, 0) < 0 && errno == ESRCH) {
daemon_log(LOG_WARNING, "Lockfile is stale. Overriding it.");
/* Yes, here is a race condition */
unlink(path);
} else
return 1;
}
}
}
u = umask(0033);
fd = open(temp, O_WRONLY | O_CREAT | O_EXCL, 0666);
umask(u);
if (fd < 0) {
daemon_log(LOG_ERR, "Failed to create temporary lock file: %s", strerror(errno));
return -1;
}
if ((pw = getpwuid(target_uid)))
username = pw->pw_name;
else
snprintf(username = uidbuf, sizeof(uidbuf), "%lu", (unsigned long) target_uid);
snprintf(buf, sizeof(buf), "%10lu %s %.20s\n", (unsigned long) getpid(), appname, username);
if (loop_write(fd, buf, strlen(buf)) < 0) {
daemon_log(LOG_ERR, "Failed to write to temporary lock file: %s", strerror(errno));
close(fd);
return -1;
}
if (fchown(fd, target_uid, target_gid) < 0) {
daemon_log(LOG_ERR, "Failed to change owners of temporary lock file: %s", strerror(errno));
close(fd);
return -1;
}
close(fd);
if (link(temp, path) < 0) {
if (errno == EEXIST)
continue;
daemon_log(LOG_ERR, "Failed to link temporary lock file: %s", strerror(errno));
}
unlink(temp);
return 0;
}
}
int device_unlock(const char *dev) {
if (unlink(lockfile(dev)) < 0) {
daemon_log(LOG_ERR, "Failed to remove lock file: %s", strerror(errno));
return -1;
}
return 0;
}
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