Subject: Re: [PATCH v1 1/2] open: add close_range()

From: Oleg Nesterov <[email-masked]>
Date: Wed, 22 May 2019 18:57:37 +0200

On 05/22, Christian Brauner wrote:
>
> +static struct file *pick_file(struct files_struct *files, unsigned fd)
>  {
> -	struct file *file;
> +	struct file *file = NULL;
>  	struct fdtable *fdt;
>  
>  	spin_lock(&files->file_lock);
> @@ -632,15 +629,65 @@ int __close_fd(struct files_struct *files, unsigned fd)
>  		goto out_unlock;
>  	rcu_assign_pointer(fdt->fd[fd], NULL);
>  	__put_unused_fd(files, fd);
> -	spin_unlock(&files->file_lock);
> -	return filp_close(file, files);
>  
>  out_unlock:
>  	spin_unlock(&files->file_lock);
> -	return -EBADF;
> +	return file;

...

> +int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd)
> +{
> +	unsigned int cur_max;
> +
> +	if (fd > max_fd)
> +		return -EINVAL;
> +
> +	rcu_read_lock();
> +	cur_max = files_fdtable(files)->max_fds;
> +	rcu_read_unlock();
> +
> +	/* cap to last valid index into fdtable */
> +	if (max_fd >= cur_max)
> +		max_fd = cur_max - 1;
> +
> +	while (fd <= max_fd) {
> +		struct file *file;
> +
> +		file = pick_file(files, fd++);

Well, how about something like

	static unsigned int find_next_opened_fd(struct fdtable *fdt, unsigned start)
	{
		unsigned int maxfd = fdt->max_fds;
		unsigned int maxbit = maxfd / BITS_PER_LONG;
		unsigned int bitbit = start / BITS_PER_LONG;

		bitbit = find_next_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
		if (bitbit > maxfd)
			return maxfd;
		if (bitbit > start)
			start = bitbit;
		return find_next_bit(fdt->open_fds, maxfd, start);
	}

	unsigned close_next_fd(struct files_struct *files, unsigned start, unsigned maxfd)
	{
		unsigned fd;
		struct file *file;
		struct fdtable *fdt;
	
		spin_lock(&files->file_lock);
		fdt = files_fdtable(files);
		fd = find_next_opened_fd(fdt, start);
		if (fd >= fdt->max_fds || fd > maxfd) {
			fd = -1;
			goto out;
		}

		file = fdt->fd[fd];
		rcu_assign_pointer(fdt->fd[fd], NULL);
		__put_unused_fd(files, fd);
	out:
		spin_unlock(&files->file_lock);

		if (fd == -1u)
			return fd;

		filp_close(file, files);
		return fd + 1;
	}

?

Then close_range() can do

	while (fd < max_fd)
		fd = close_next_fd(fd, maxfd);

Oleg.