when and where does ep_poll_callback be called ?

when and where does ep_poll_callback be called ?

[horseriver]

hi:


   I'm studying the epoll module , I can not find ep_poll_callback be called somewhere .
   
  


thanks!

Re: when and where does ep_poll_callback be called ?

[Randy Dunlap]

On 01/13/13 17:11, horseriver wrote:
> hi:
> 
> 
>    I'm studying the epoll module , I can not find ep_poll_callback be called somewhere .


It's right there in fs/eventpoll.c:


/*
 * This is the callback that is used to add our wait queue to the
 * target file wakeup lists.
 */
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
				 poll_table *pt)
{
	struct epitem *epi = ep_item_from_epqueue(pt);
	struct eppoll_entry *pwq;

	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
>>>>>		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
		pwq->whead = whead;
		pwq->base = epi;
		add_wait_queue(whead, &pwq->wait);
		list_add_tail(&pwq->llink, &epi->pwqlist);
		epi->nwait++;



-- 
~Randy

Re: when and where does ep_poll_callback be called ?

[horseriver]

On Mon, Jan 14, 2013 at 08:35:29AM -0800, Randy Dunlap wrote:
> On 01/13/13 17:11, horseriver wrote:
> > hi:
> > 
> > 
> >    I'm studying the epoll module , I can not find ep_poll_callback be called somewhere .
> 
> 
> It's right there in fs/eventpoll.c:
> 
> 
> /*
>  * This is the callback that is used to add our wait queue to the
>  * target file wakeup lists.
>  */
> static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
> 				 poll_table *pt)
> {
> 	struct epitem *epi = ep_item_from_epqueue(pt);
> 	struct eppoll_entry *pwq;
> 
> 	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
> >>>>>		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);

     Thanks!
     
     I know this is setting  the callbak function into watqueue . But not the called place . 

     I want to know the code which calls  ep_poll_callback .

     Perhaps , it is called at tcp layer when a datagram is reached . but I have not find that key  code .

     

> 		pwq->whead = whead;
> 		pwq->base = epi;
> 		add_wait_queue(whead, &pwq->wait);
> 		list_add_tail(&pwq->llink, &epi->pwqlist);
> 		epi->nwait++;
> 
> 
> 
> -- 
> ~Randy

Re: when and where does ep_poll_callback be called ?

[Eric Dumazet]

On Mon, 2013-01-14 at 09:11 +0800, horseriver wrote:
> hi:
> 
> 
>    I'm studying the epoll module , I can not find ep_poll_callback be called somewhere .
>    
>   

Thats more a lkml question.

But you can figure it yourself :

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 9fec183..c6e7490 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -928,6 +928,7 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
 	struct epitem *epi = ep_item_from_wait(wait);
 	struct eventpoll *ep = epi->ep;
 
+	WARN_ON_ONCE(1);
 	if ((unsigned long)key & POLLFREE) {
 		ep_pwq_from_wait(wait)->whead = NULL;
 		/*