linux-kernel - Re: [RFC] Hack to use mkdir/rmdir in debugfs

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Date:	Tue, 22 Jan 2013 22:47:01 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] Hack to use mkdir/rmdir in debugfs

On Tue, 2013-01-22 at 22:01 -0500, Steven Rostedt wrote:

> As you can see, I haven't implemented the rmdir yet.

I decided to implement this too :-)

static int instance_rmdir(struct inode *inode, struct dentry *dentry)
{
	struct dentry *parent;
	int ret;

	/* Paranoid: Make sure the parent is the "instances" directory */
	parent = hlist_entry(inode->i_dentry.first, struct dentry, d_alias);
	if (WARN_ON_ONCE(parent != trace_instance_dir))
		return -ENOENT;

	/* The caller did a dget() on dentry */
	mutex_unlock(&dentry->d_inode->i_mutex);

	/*
	 * The inode mutex is locked, but debugfs_create_dir() will also
	 * take the mutex. As the instances directory can not be destroyed
	 * or changed in any other way, it is safe to unlock it, and
	 * let the dentry try. If two users try to make the same dir at
	 * the same time, then the instance_delete() will determine the
	 * winner.
	 */
	mutex_unlock(&inode->i_mutex);

	ret = instance_delete(dentry->d_iname);

	mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
	mutex_lock(&dentry->d_inode->i_mutex);

	return ret;
}

static const struct inode_operations instance_dir_inode_operations = {
	.lookup		= simple_lookup,
	.mkdir		= instance_mkdir,
	.rmdir		= instance_rmdir,
};


I ran it under lockdep and it didn't complain.

-- Steve



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