linux-kernel - Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers

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Date:	Mon, 12 Feb 2007 20:57:38 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	menage@...gle.com
Cc:	akpm@...l.org, pj@....com, sekharan@...ibm.com, dev@...ru,
	xemul@...ru, serue@...ibm.com, ebiederm@...ssion.com,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	rohitseth@...gle.com, mbligh@...gle.com, winget@...gle.com,
	containers@...ts.osdl.org, devel@...nvz.org
Subject: Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers

On Mon, Feb 12, 2007 at 12:15:24AM -0800, menage@...gle.com wrote:
> +/*
> + * Call css_get() to hold a reference on the container; following a
> + * return of 0, this container subsystem state object is guaranteed
> + * not to be destroyed until css_put() is called on it.  A non-zero
> + * return code indicates that a reference could not be taken.
> + *
> + */
> +

Why can't we reuse container->count (or container_group->ref) to
refcount the per-subsystem object attached to a container? I think
that is how it is done for cpusets? That would make css_get/put
unnecessary?

> +static inline int css_get(struct container_subsys_state *css)
> +{
> +	int retval = 0;
> +	unsigned long flags;
> +	/* Synchronize with container_rmdir() */
> +	spin_lock_irqsave(&css->refcnt_lock, flags);
> +	if (atomic_read(&css->refcnt) >= 0) {
> +		/* Container is still alive */
> +		atomic_inc(&css->refcnt);
> +	} else {
> +		/* Container removal is in progress */
> +		retval = -EINVAL;
> +	}
> +	spin_unlock_irqrestore(&css->refcnt_lock, flags);
> +	return retval;
> +}

-- 
Regards,
vatsa
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