linux-kernel - Re: [PATCH] epoll: use wrapper functions

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Date:	Thu, 6 May 2010 11:47:27 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Changli Gao <xiaosuo@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Roland Dreier <rolandd@...co.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Takashi Iwai <tiwai@...e.de>,
	David Howells <dhowells@...hat.com>,
	linux-fsdevel@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] epoll: use wrapper functions

On Thu, 6 May 2010, Changli Gao wrote:

> use wrapper functions.
> 
> epoll should not touch flags in wait_queue_t. This patch introduces a new
> function add_wait_queue_head_exclusive_locked(), for the users, who use
> wait queue as a LIFO queue.

Since we already have __add_wait_queue(), __add_wait_queue_tail() and 
__remove_wait_queue() (which all means "locked"), and while I agree in 
having the exclusive-add wrapped into a function, I much better prefer a:

static inline void __add_wait_queue_excl(wait_queue_head_t *head, 
					 wait_queue_t *new)
{
	new->flags |= WQ_FLAG_EXCLUSIVE;
	__add_wait_queue(head, new);
}

The patch you posted introduces a different naming, which leaves all the 
other __*() untouched, and wraps the already one-liner __remove_wait_queue() 
with yet another one-liner.





> Signed-off-by: Changli Gao <xiaosuo@...il.com>
> ----
>  fs/eventpoll.c       |    5 ++---
>  include/linux/wait.h |   15 +++++++++++++--
>  2 files changed, 15 insertions(+), 5 deletions(-)
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index bd056a5..8137f6e 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1140,8 +1140,7 @@ retry:
>  		 * ep_poll_callback() when events will become available.
>  		 */
>  		init_waitqueue_entry(&wait, current);
> -		wait.flags |= WQ_FLAG_EXCLUSIVE;
> -		__add_wait_queue(&ep->wq, &wait);
> +		add_wait_queue_head_exclusive_locked(&ep->wq, &wait);
>  
>  		for (;;) {
>  			/*
> @@ -1161,7 +1160,7 @@ retry:
>  			jtimeout = schedule_timeout(jtimeout);
>  			spin_lock_irqsave(&ep->lock, flags);
>  		}
> -		__remove_wait_queue(&ep->wq, &wait);
> +		remove_wait_queue_locked(&ep->wq, &wait);
>  
>  		set_current_state(TASK_RUNNING);
>  	}
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index a48e16b..de2566d 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -407,17 +407,28 @@ do {									\
>   * Must be called with the spinlock in the wait_queue_head_t held.
>   */
>  static inline void add_wait_queue_exclusive_locked(wait_queue_head_t *q,
> -						   wait_queue_t * wait)
> +						   wait_queue_t *wait)
>  {
>  	wait->flags |= WQ_FLAG_EXCLUSIVE;
>  	__add_wait_queue_tail(q,  wait);
>  }
>  
>  /*
> + * Must be called with the spinlock in the wait_queue_head_t held, and
> + * q must be for exclusive wait only.
> + */
> +static inline void add_wait_queue_head_exclusive_locked(wait_queue_head_t *q,
> +							wait_queue_t *wait)
> +{
> +	wait->flags |= WQ_FLAG_EXCLUSIVE;
> +	__add_wait_queue(q,  wait);
> +}
> +
> +/*
>   * Must be called with the spinlock in the wait_queue_head_t held.
>   */
>  static inline void remove_wait_queue_locked(wait_queue_head_t *q,
> -					    wait_queue_t * wait)
> +					    wait_queue_t *wait)
>  {
>  	__remove_wait_queue(q,  wait);
>  }
> --
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> 


- Davide


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