linux-kernel - Re: [PATCH v1 1/2] open: add close

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Date:   Wed, 22 May 2019 18:57:37 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        torvalds@...ux-foundation.org, fweimer@...hat.com,
        jannh@...gle.com, tglx@...utronix.de, arnd@...db.de,
        shuah@...nel.org, dhowells@...hat.com, tkjos@...roid.com,
        ldv@...linux.org, miklos@...redi.hu, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v1 1/2] open: add close_range()

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.