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#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <utmp.h>
static const char *utmp_file_name = _PATH_UTMP;
static int fd = -1;
static int lock_record(int type) {
struct flock fl;
fl.l_whence = SEEK_CUR;
fl.l_start = 0;
fl.l_len = sizeof(struct utmp);
fl.l_pid = 0;
fl.l_type = type;
return fcntl(fd, F_SETLKW, &fl);
}
static int unlock_record() {
struct flock fl;
fl.l_whence = SEEK_CUR;
fl.l_start = -sizeof(struct utmp);
fl.l_len = sizeof(struct utmp);
fl.l_pid = 0;
fl.l_type = F_UNLCK;
return fcntl(fd, F_SETLK, &fl);
}
void utmpname(const char *file) {
if (file)
utmp_file_name = file;
else
utmp_file_name = _PATH_UTMP;
}
void setutent() {
if (fd<0) fd = open(utmp_file_name,O_RDWR);
if (fd<0) fd = open(utmp_file_name,O_RDONLY);
fcntl (fd, F_SETFD, FD_CLOEXEC);
lseek(fd,0,SEEK_SET);
}
void endutent() {
if (fd<0) return;
close(fd); fd=-1;
}
struct utmp *getutent(void) {
static struct utmp getutent_tmp;
int ret;
if (fd<0) {
setutent();
if (fd<0) return 0;
}
if (lock_record(F_RDLCK)) return 0;
ret=read(fd, &getutent_tmp, sizeof(struct utmp));
unlock_record();
if (ret<1) return 0;
return &getutent_tmp;
}
struct utmp *getutid(struct utmp *ut) {
struct utmp *tmp;
while ((tmp = getutent())) {
if (ut->ut_type && (ut->ut_type <= OLD_TIME)) {
if (ut->ut_type == tmp->ut_type) break;
}
if ((ut->ut_type >= INIT_PROCESS) && (ut->ut_type <= DEAD_PROCESS)) {
if (!strncmp(ut->ut_id,tmp->ut_id,4)) break;
}
}
return tmp;
}
struct utmp *getutline(struct utmp *ut) {
struct utmp *tmp;
while ((tmp = getutent())) {
if ((tmp->ut_type == USER_PROCESS) || (tmp->ut_type == LOGIN_PROCESS)) {
if (!strncmp(ut->ut_line,tmp->ut_line,UT_LINESIZE)) break;
}
}
return tmp;
}
void pututline(struct utmp *ut) {
struct utmp *tmp;
if ((tmp = getutid(ut))) {
lseek(fd, - (off_t)sizeof(struct utmp), SEEK_CUR);
if (lock_record(F_WRLCK)) return;
write(fd, ut, sizeof(struct utmp));
}
else {
lseek(fd, 0, SEEK_END);
if (lock_record(F_WRLCK)) return;
write(fd, ut, (off_t)sizeof(struct utmp));
}
unlock_record();
}
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