int
sys_open(void)
{
  char *path;
  int fd, omode;
  struct file *f;
  struct inode *ip;

  if(argstr(0, &path) < 0 || argint(1, &omode) < 0)
    return -1;
  ip = namei(path);
  if (ip == 0) {
    if(omode & O_CREATE){
      int mode;
      if (argint(2, &mode) < 0 || !check_permissions(mode))
        return -1;
      begin_trans();
      ip = create(path, T_FILE, 0, 0, proc->euid, (uint)mode);
      commit_trans();
      if(ip == 0) {
        return -1;
      }
    } else {
      return -1;
    }
  } else {
    ilock(ip);
  }
  // by this moment we hold ip
  if (ip->type == T_MUTEX) {
    iunlockput(ip);
    return -1;
  }

  if(ip->type == T_DIR && omode != O_RDONLY){
    iunlockput(ip);
    return -1;
  }
  if (((omode & O_WRONLY) || (omode & O_RDWR)) && !can_write(ip)) {
    iunlockput(ip);
    return -1;
  }
  if (!(omode & O_WRONLY) && !can_read(ip)) {
    iunlockput(ip);
    return -1;
  }

  if (ip->type == T_FIFO) {
    if (omode & O_RDWR)
      goto fail_put;
    if (ip->pipe == 0) {
      ip->pipe = fifo_pipe_alloc(ip);
      if (ip->pipe == 0)
        goto fail_put;
    }
    struct pipe *pipe = ip->pipe;
    /* the situation with locks and channels here is a bit messy, so
       pipe->lock is used to protect pipe->readopen AND pipe->writeopen
       &pipe->readopen is used to wait for the reader */

    acquire(&pipe->lock);
    iunlock(ip);
    if (omode == O_RDONLY) {
      struct file *f = fifo_file_alloc(pipe, 0);
      while (pipe->writeopen == 0) {
        wakeup(&pipe->readopen);
        sleep(&pipe->writeopen, &pipe->lock);
      }
      wakeup(&pipe->readopen);
      release(&pipe->lock);
      fd = fdalloc(f);
    } else {
      struct file *f = fifo_file_alloc(pipe, 1);
      while (pipe->readopen == 0) {
        wakeup(&pipe->writeopen);
        sleep(&pipe->readopen, &pipe->lock);
      }
      wakeup(&pipe->writeopen);
      release(&pipe->lock);
      fd = fdalloc(f);
    }
    if (fd < 0)
      goto fail;
    return fd;
fail_put:
    iunlockput(ip);
    return -1;
fail:
    iunlock(ip);
    return -1;
  }

  if((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0){
    if(f)
      fileclose(f);
    iunlockput(ip);
    return -1;
  }
  iunlock(ip);

  f->type = FD_INODE;
  f->ip = ip;
  f->off = 0;
  f->readable = !(omode & O_WRONLY);
  f->writable = (omode & O_WRONLY) || (omode & O_RDWR);
  return fd;
}

int
sys_mkdir(void)
{
  char *path;
  struct inode *ip;
  int mode;

  begin_trans();
  if(argstr(0, &path) < 0 || argint(1, &mode) < 0 || !check_permissions(mode) || (ip = create(path, T_DIR, 0, 0, proc->euid, (uint)mode)) == 0){
    commit_trans();
    return -1;
  }
  iunlockput(ip);
  commit_trans();
  return 0;
}