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/*

 * Copyright (C) 2006 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup sync

 * @{

 */

/**

 * @file

 * @brief	Kernel backend for futexes.

 */

#include <synch/futex.h>

#include <synch/rwlock.h>

#include <synch/spinlock.h>

#include <synch/synch.h>

#include <mm/frame.h>

#include <mm/page.h>

#include <mm/slab.h>

#include <proc/thread.h>

#include <proc/task.h>

#include <genarch/mm/page_pt.h>

#include <genarch/mm/page_ht.h>

#include <adt/hash_table.h>

#include <adt/list.h>

#include <arch.h>

#include <align.h>

#include <panic.h>

#include <errno.h>

#include <print.h>

#define FUTEX_HT_SIZE	1024	/* keep it a power of 2 */

static void futex_initialize(futex_t *futex);

static futex_t *futex_find(uintptr_t paddr);

static index_t futex_ht_hash(unative_t *key);

static bool futex_ht_compare(unative_t *key, count_t keys, link_t *item);

static void futex_ht_remove_callback(link_t *item);

/**

 * Read-write lock protecting global futex hash table.

 * It is also used to serialize access to all futex_t structures.

 * Must be acquired before the task futex B+tree lock.

 */

static rwlock_t futex_ht_lock;

/** Futex hash table. */

static hash_table_t futex_ht;

/** Futex hash table operations. */

static hash_table_operations_t futex_ht_ops = {

	.hash = futex_ht_hash,

	.compare = futex_ht_compare,

	.remove_callback = futex_ht_remove_callback

};

/** Initialize futex subsystem. */

void futex_init(void)

{

	rwlock_initialize(&futex_ht_lock);

	hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);

}

/** Initialize kernel futex structure.

 *

 * @param futex Kernel futex structure.

 */

void futex_initialize(futex_t *futex)

{

	waitq_initialize(&futex->wq);

	link_initialize(&futex->ht_link);

	futex->paddr = 0;

	futex->refcount = 1;

}

/** Sleep in futex wait queue.

 *

 * @param uaddr Userspace address of the futex counter.

 * @param usec If non-zero, number of microseconds this thread is willing to sleep.

 * @param flags Select mode of operation.

 *

 * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See synch.h.

 *	   If there is no physical mapping for uaddr ENOENT is returned.

 */

unative_t sys_futex_sleep_timeout(uintptr_t uaddr, uint32_t usec, int flags)

{

	futex_t *futex;

	uintptr_t paddr;

	pte_t *t;

	ipl_t ipl;

	ipl = interrupts_disable();

	/*

	 * Find physical address of futex counter.

	 */

	page_table_lock(AS, true);

	t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));

	if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {

		page_table_unlock(AS, true);

		interrupts_restore(ipl);

		return (unative_t) ENOENT;

	}

	paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));

	page_table_unlock(AS, true);

	interrupts_restore(ipl);	

	futex = futex_find(paddr);

	return (unative_t) waitq_sleep_timeout(&futex->wq, usec, flags | SYNCH_FLAGS_INTERRUPTIBLE);

}

/** Wakeup one thread waiting in futex wait queue.

 *

 * @param uaddr Userspace address of the futex counter.

 *

 * @return ENOENT if there is no physical mapping for uaddr.

 */

unative_t sys_futex_wakeup(uintptr_t uaddr)

{

	futex_t *futex;

	uintptr_t paddr;

	pte_t *t;

	ipl_t ipl;

	ipl = interrupts_disable();

	/*

	 * Find physical address of futex counter.

	 */

	page_table_lock(AS, true);

	t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));

	if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {

		page_table_unlock(AS, true);

		interrupts_restore(ipl);

		return (unative_t) ENOENT;

	}

	paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));

	page_table_unlock(AS, true);

	interrupts_restore(ipl);

	futex = futex_find(paddr);

	waitq_wakeup(&futex->wq, WAKEUP_FIRST);

	return 0;

}

/** Find kernel address of the futex structure corresponding to paddr.

 *

 * If the structure does not exist already, a new one is created.

 *

 * @param paddr Physical address of the userspace futex counter.

 *

 * @return Address of the kernel futex structure.

 */

futex_t *futex_find(uintptr_t paddr)

{

	link_t *item;

	futex_t *futex;

	btree_node_t *leaf;

	/*

	 * Find the respective futex structure

	 * or allocate new one if it does not exist already.

	 */

	rwlock_read_lock(&futex_ht_lock);

	item = hash_table_find(&futex_ht, &paddr);

	if (item) {

		futex = hash_table_get_instance(item, futex_t, ht_link);

		/*

		 * See if the current task knows this futex.

		 */

		mutex_lock(&TASK->futexes_lock);

		if (!btree_search(&TASK->futexes, paddr, &leaf)) {

			/*

			 * The futex is new to the current task.

			 * However, we only have read access.

			 * Gain write access and try again.

			 */

			mutex_unlock(&TASK->futexes_lock);

			goto gain_write_access;

		}

		mutex_unlock(&TASK->futexes_lock);

		rwlock_read_unlock(&futex_ht_lock);

	} else {

gain_write_access:

		/*

		 * Upgrade to writer is not currently supported,

		 * therefore, it is necessary to release the read lock

		 * and reacquire it as a writer.

		 */

		rwlock_read_unlock(&futex_ht_lock);

		rwlock_write_lock(&futex_ht_lock);

		/*

		 * Avoid possible race condition by searching

		 * the hash table once again with write access.

		 */

		item = hash_table_find(&futex_ht, &paddr);

		if (item) {

			futex = hash_table_get_instance(item, futex_t, ht_link);

			/*

			 * See if this futex is known to the current task.

			 */

			mutex_lock(&TASK->futexes_lock);

			if (!btree_search(&TASK->futexes, paddr, &leaf)) {

				/*

				 * The futex is new to the current task.

				 * Upgrade its reference count and put it to the

				 * current task's B+tree of known futexes.

				 */

				futex->refcount++;

				btree_insert(&TASK->futexes, paddr, futex, leaf);

			}

			mutex_unlock(&TASK->futexes_lock);

			rwlock_write_unlock(&futex_ht_lock);

		} else {

			futex = (futex_t *) malloc(sizeof(futex_t), 0);

			futex_initialize(futex);

			futex->paddr = paddr;

			hash_table_insert(&futex_ht, &paddr, &futex->ht_link);

			/*

			 * This is the first task referencing the futex.

			 * It can be directly inserted into its

			 * B+tree of known futexes.

			 */

			mutex_lock(&TASK->futexes_lock);

			btree_insert(&TASK->futexes, paddr, futex, NULL);

			mutex_unlock(&TASK->futexes_lock);

			rwlock_write_unlock(&futex_ht_lock);

		}

	}

	return futex;

}

/** Compute hash index into futex hash table.

 *

 * @param key Address where the key (i.e. physical address of futex counter) is stored.

 *

 * @return Index into futex hash table.

 */

index_t futex_ht_hash(unative_t *key)

{

	return *key & (FUTEX_HT_SIZE-1);

}

/** Compare futex hash table item with a key.

 *

 * @param key Address where the key (i.e. physical address of futex counter) is stored.

 *

 * @return True if the item matches the key. False otherwise.

 */

bool futex_ht_compare(unative_t *key, count_t keys, link_t *item)

{

	futex_t *futex;

	ASSERT(keys == 1);

	futex = hash_table_get_instance(item, futex_t, ht_link);

	return *key == futex->paddr;

}

/** Callback for removal items from futex hash table.

 *

 * @param item Item removed from the hash table.

 */

void futex_ht_remove_callback(link_t *item)

{

	futex_t *futex;

	futex = hash_table_get_instance(item, futex_t, ht_link);

	free(futex);

}

/** Remove references from futexes known to the current task. */

void futex_cleanup(void)

{

	link_t *cur;

	rwlock_write_lock(&futex_ht_lock);

	mutex_lock(&TASK->futexes_lock);

	for (cur = TASK->futexes.leaf_head.next; cur != &TASK->futexes.leaf_head; cur = cur->next) {

		btree_node_t *node;

		int i;

		node = list_get_instance(cur, btree_node_t, leaf_link);

		for (i = 0; i < node->keys; i++) {

			futex_t *ftx;

			uintptr_t paddr = node->key[i];

			ftx = (futex_t *) node->value[i];

			if (--ftx->refcount == 0)

				hash_table_remove(&futex_ht, &paddr, 1);

		}

	}

	mutex_unlock(&TASK->futexes_lock);

	rwlock_write_unlock(&futex_ht_lock);

}

/** @}

 */