linux-kernel - Re: [RFC v10][PATCH 08/13] Dump open file descriptors

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Date:	Fri, 28 Nov 2008 10:19:19 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Serge Hallyn <serue@...ibm.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC v10][PATCH 08/13] Dump open file descriptors

On Wed, Nov 26, 2008 at 08:04:39PM -0500, Oren Laadan wrote:
> +int cr_scan_fds(struct files_struct *files, int **fdtable)
> +{
> +	struct fdtable *fdt;
> +	int *fds;
> +	int i, n = 0;
> +	int tot = CR_DEFAULT_FDTABLE;
> +
> +	fds = kmalloc(tot * sizeof(*fds), GFP_KERNEL);
> +	if (!fds)
> +		return -ENOMEM;
> +
> +	/*
> +	 * We assume that the target task is frozen (or that we checkpoint
> +	 * ourselves), so we can safely proceed after krealloc() from where
> +	 * we left off; in the worst cases restart will fail.
> +	 */

Task may be frozen, but it may share the table with any number of other
tasks...

> +	spin_lock(&files->file_lock);
> +	rcu_read_lock();
> +	fdt = files_fdtable(files);
> +	for (i = 0; i < fdt->max_fds; i++) {
> +		if (!fcheck_files(files, i))
> +			continue;
> +		if (n == tot) {
> +			/*
> +			 * fcheck_files() is safe with drop/re-acquire
> +			 * of the lock, because it tests:  fd < max_fds
> +			 */
> +			spin_unlock(&files->file_lock);
> +			rcu_read_unlock();
> +			tot *= 2;	/* won't overflow: kmalloc will fail */
> +			fds = krealloc(fds, tot * sizeof(*fds), GFP_KERNEL);
> +			if (!fds)
> +				return -ENOMEM;
> +			rcu_read_lock();
> +			spin_lock(&files->file_lock);
> +		}
> +		fds[n++] = i;
> +	}
> +	rcu_read_unlock();
> +	spin_unlock(&files->file_lock);
> +
> +	*fdtable = fds;
> +	return n;
> +}

> +	switch (inode->i_mode & S_IFMT) {
> +	case S_IFREG:
> +		fd_type = CR_FD_FILE;
> +		break;
> +	case S_IFDIR:
> +		fd_type = CR_FD_DIR;
> +		break;
> +	case S_IFLNK:
> +		fd_type = CR_FD_LINK;

Opened symlinks?  May I have whatever you'd been smoking, please?
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