[PATCH] sem2mutex: eventpoll

#include <linux/eventpoll.h>

#include <linux/mount.h>

#include <linux/bitops.h>

#include <linux/mutex.h>

#include <asm/uaccess.h>

#include <asm/system.h>

#include <asm/io.h>

 * LOCKING:

 * There are three level of locking required by epoll :

 *

 * 1) epsem (semaphore)

 * 1) epmutex (mutex)

 * 2) ep->sem (rw_semaphore)

 * 3) ep->lock (rw_lock)

 *

 * if a file has been pushed inside an epoll set and it is then

 * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).

 * It is possible to drop the "ep->sem" and to use the global

 * semaphore "epsem" (together with "ep->lock") to have it working,

 * semaphore "epmutex" (together with "ep->lock") to have it working,

 * but having "ep->sem" will make the interface more scalable.

 * Events that require holding "epsem" are very rare, while for

 * Events that require holding "epmutex" are very rare, while for

 * normal operations the epoll private "ep->sem" will guarantee

 * a greater scalability.

 */

/*

 * This semaphore is used to serialize ep_free() and eventpoll_release_file().

 */

static struct semaphore epsem;

static struct mutex epmutex;

/* Safe wake up implementation */

static struct poll_safewake psw;

	 * cleanup path, and this means that noone is using this file anymore.

	 * The only hit might come from ep_free() but by holding the semaphore

	 * will correctly serialize the operation. We do need to acquire

	 * "ep->sem" after "epsem" because ep_remove() requires it when called

	 * "ep->sem" after "epmutex" because ep_remove() requires it when called

	 * from anywhere but ep_free().

	 */

	down(&epsem);

	mutex_lock(&epmutex);

	while (!list_empty(lsthead)) {

		epi = list_entry(lsthead->next, struct epitem, fllink);

		up_write(&ep->sem);

	}

	up(&epsem);

	mutex_unlock(&epmutex);

}

	 * We do not need to hold "ep->sem" here because the epoll file

	 * is on the way to be removed and no one has references to it

	 * anymore. The only hit might come from eventpoll_release_file() but

	 * holding "epsem" is sufficent here.

	 * holding "epmutex" is sufficent here.

	 */

	down(&epsem);

	mutex_lock(&epmutex);

	/*

	 * Walks through the whole tree by unregistering poll callbacks.

		ep_remove(ep, epi);

	}

	up(&epsem);

	mutex_unlock(&epmutex);

}

{

	int error;

	init_MUTEX(&epsem);

	mutex_init(&epmutex);

	/* Initialize the structure used to perform safe poll wait head wake ups */

	ep_poll_safewake_init(&psw);