#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include "syscall.h"

void __procfdname(char*, unsigned);

int fchmodat(int fd, const char* path, mode_t mode, int flag) {
  if (!flag)
    return syscall(SYS_fchmodat, fd, path, mode, flag);

  if (flag != AT_SYMLINK_NOFOLLOW)
    return __syscall_ret(-EINVAL);

  struct stat st;
  int ret, fd2;
  char proc[15 + 3 * sizeof(int)];

  if ((ret = __syscall(SYS_fstatat, fd, path, &st, flag)))
    return __syscall_ret(ret);
  if (S_ISLNK(st.st_mode))
    return __syscall_ret(-EOPNOTSUPP);

  if ((fd2 = __syscall(SYS_openat, fd, path, O_RDONLY | O_PATH | O_NOFOLLOW |
                                                 O_NOCTTY | O_CLOEXEC)) < 0) {
    if (fd2 == -ELOOP)
      return __syscall_ret(-EOPNOTSUPP);
    return __syscall_ret(fd2);
  }

  __procfdname(proc, fd2);
  ret = __syscall(SYS_fstatat, AT_FDCWD, proc, &st, 0);
  if (!ret) {
    if (S_ISLNK(st.st_mode))
      ret = -EOPNOTSUPP;
    else
      ret = __syscall(SYS_fchmodat, AT_FDCWD, proc, mode);
  }

  __syscall(SYS_close, fd2);
  return __syscall_ret(ret);
}