linux-kernel - Re: [PATCH] nextfd(2)

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Message-ID: <1333295005.2325.5204.camel@edumazet-glaptop>
Date:	Sun, 01 Apr 2012 17:43:25 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, drepper@...il.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

On Sun, 2012-04-01 at 15:57 +0300, Alexey Dobriyan wrote:

> +
> +/* Return first opened file descriptor which is >= than the argument. */
> +SYSCALL_DEFINE1(nextfd, unsigned int, fd)
> +{
> +	struct files_struct *files = current->files;
> +	struct fdtable *fdt;
> +
> +	rcu_read_lock();
> +	fdt = files_fdtable(files);
> +	while (fd < fdt->max_fds) {
> +		struct file *file;
> +
> +		file = rcu_dereference_check_fdtable(files, fdt->fd[fd]);
> +		if (file) {
> +			rcu_read_unlock();
> +			return fd;
> +		}
> +		fd++;
> +	}
> +	rcu_read_unlock();
> +	return -ESRCH;
> +}

Interesting idea but what about using fdt->open_fds bitmap to have a
fast search and less cache pollution ?

alloc_fd(start, flags) uses find_next_zero_bit(), you could use
find_next_bit().




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