third_party/ulib/musl/src/misc/lockf.c

#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

int lockf(int fd, int op, off_t size) {
    struct flock l = {
        .l_type = F_WRLCK, .l_whence = SEEK_CUR, .l_len = size,
    };
    switch (op) {
    case F_TEST:
        l.l_type = F_RDLCK;
        if (fcntl(fd, F_GETLK, &l) < 0)
            return -1;
        if (l.l_type == F_UNLCK || l.l_pid == getpid())
            return 0;
        errno = EACCES;
        return -1;
    case F_ULOCK:
        l.l_type = F_UNLCK;
    case F_TLOCK:
        return fcntl(fd, F_SETLK, &l);
    case F_LOCK:
        return fcntl(fd, F_SETLKW, &l);
    }
    errno = EINVAL;
    return -1;
}