writeback: speed up writeback of big dirty files

[wrt350n-kernel.git] / net / irda / irqueue.c

/*********************************************************************
 *
 * Filename:      irqueue.c
 * Version:       0.3
 * Description:   General queue implementation
 * Status:        Experimental.
 * Author:        Dag Brattli <dagb@cs.uit.no>
 * Created at:    Tue Jun  9 13:29:31 1998
 * Modified at:   Sun Dec 12 13:48:22 1999
 * Modified by:   Dag Brattli <dagb@cs.uit.no>
 * Modified at:   Thu Jan  4 14:29:10 CET 2001
 * Modified by:   Marc Zyngier <mzyngier@freesurf.fr>
 *
 *     Copyright (C) 1998-1999, Aage Kvalnes <aage@cs.uit.no>
 *     Copyright (C) 1998, Dag Brattli,
 *     All Rights Reserved.
 *
 *     This code is taken from the Vortex Operating System written by Aage
 *     Kvalnes. Aage has agreed that this code can use the GPL licence,
 *     although he does not use that licence in his own code.
 *
 *     This copyright does however _not_ include the ELF hash() function
 *     which I currently don't know which licence or copyright it
 *     has. Please inform me if you know.
 *
 *     This program is free software; you can redistribute it and/or
 *     modify it under the terms of the GNU General Public License as
 *     published by the Free Software Foundation; either version 2 of
 *     the License, or (at your option) any later version.
 *
 *     Neither Dag Brattli nor University of Tromsø admit liability nor
 *     provide warranty for any of this software. This material is
 *     provided "AS-IS" and at no charge.
 *
 ********************************************************************/

/*
 * NOTE :
 * There are various problems with this package :
 *      o the hash function for ints is pathetic (but could be changed)
 *      o locking is sometime suspicious (especially during enumeration)
 *      o most users have only a few elements (== overhead)
 *      o most users never use seach, so don't benefit from hashing
 * Problem already fixed :
 *      o not 64 bit compliant (most users do hashv = (int) self)
 *      o hashbin_remove() is broken => use hashbin_remove_this()
 * I think most users would be better served by a simple linked list
 * (like include/linux/list.h) with a global spinlock per list.
 * Jean II
 */

/*
 * Notes on the concurrent access to hashbin and other SMP issues
 * -------------------------------------------------------------
 *      Hashbins are very often in the IrDA stack a global repository of
 * information, and therefore used in a very asynchronous manner following
 * various events (driver calls, timers, user calls...).
 *      Therefore, very often it is highly important to consider the
 * management of concurrent access to the hashbin and how to guarantee the
 * consistency of the operations on it.
 *
 *      First, we need to define the objective of locking :
 *              1) Protect user data (content pointed by the hashbin)
 *              2) Protect hashbin structure itself (linked list in each bin)
 *
 *                           OLD LOCKING
 *                           -----------
 *
 *      The previous locking strategy, either HB_LOCAL or HB_GLOBAL were
 * both inadequate in *both* aspect.
 *              o HB_GLOBAL was using a spinlock for each bin (local locking).
 *              o HB_LOCAL was disabling irq on *all* CPUs, so use a single
 *                global semaphore.
 *      The problems were :
 *              A) Global irq disabling is no longer supported by the kernel
 *              B) No protection for the hashbin struct global data
 *                      o hashbin_delete()
 *                      o hb_current
 *              C) No protection for user data in some cases
 *
 *      A) HB_LOCAL use global irq disabling, so doesn't work on kernel
 * 2.5.X. Even when it is supported (kernel 2.4.X and earlier), its
 * performance is not satisfactory on SMP setups. Most hashbins were
 * HB_LOCAL, so (A) definitely need fixing.
 *      B) HB_LOCAL could be modified to fix (B). However, because HB_GLOBAL
 * lock only the individual bins, it will never be able to lock the
 * global data, so can't do (B).
 *      C) Some functions return pointer to data that is still in the
 * hashbin :
 *              o hashbin_find()
 *              o hashbin_get_first()
 *              o hashbin_get_next()
 *      As the data is still in the hashbin, it may be changed or free'd
 * while the caller is examinimg the data. In those case, locking can't
 * be done within the hashbin, but must include use of the data within
 * the caller.
 *      The caller can easily do this with HB_LOCAL (just disable irqs).
 * However, this is impossible with HB_GLOBAL because the caller has no
 * way to know the proper bin, so don't know which spinlock to use.
 *
 *      Quick summary : can no longer use HB_LOCAL, and HB_GLOBAL is
 * fundamentally broken and will never work.
 *
 *                           NEW LOCKING
 *                           -----------
 *
 *      To fix those problems, I've introduce a few changes in the
 * hashbin locking :
 *              1) New HB_LOCK scheme
 *              2) hashbin->hb_spinlock
 *              3) New hashbin usage policy
 *
 * HB_LOCK :
 * -------
 *      HB_LOCK is a locking scheme intermediate between the old HB_LOCAL
 * and HB_GLOBAL. It uses a single spinlock to protect the whole content
 * of the hashbin. As it is a single spinlock, it can protect the global
 * data of the hashbin and not only the bins themselves.
 *      HB_LOCK can only protect some of the hashbin calls, so it only lock
 * call that can be made 100% safe and leave other call unprotected.
 *      HB_LOCK in theory is slower than HB_GLOBAL, but as the hashbin
 * content is always small contention is not high, so it doesn't matter
 * much. HB_LOCK is probably faster than HB_LOCAL.
 *
 * hashbin->hb_spinlock :
 * --------------------
 *      The spinlock that HB_LOCK uses is available for caller, so that
 * the caller can protect unprotected calls (see below).
 *      If the caller want to do entirely its own locking (HB_NOLOCK), he
 * can do so and may use safely this spinlock.
 *      Locking is done like this :
 *              spin_lock_irqsave(&hashbin->hb_spinlock, flags);
 *      Releasing the lock :
 *              spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
 *
 * Safe & Protected calls :
 * ----------------------
 *      The following calls are safe or protected via HB_LOCK :
 *              o hashbin_new()         -> safe
 *              o hashbin_delete()
 *              o hashbin_insert()
 *              o hashbin_remove_first()
 *              o hashbin_remove()
 *              o hashbin_remove_this()
 *              o HASHBIN_GET_SIZE()    -> atomic
 *
 *      The following calls only protect the hashbin itself :
 *              o hashbin_lock_find()
 *              o hashbin_find_next()
 *
 * Unprotected calls :
 * -----------------
 *      The following calls need to be protected by the caller :
 *              o hashbin_find()
 *              o hashbin_get_first()
 *              o hashbin_get_next()
 *
 * Locking Policy :
 * --------------
 *      If the hashbin is used only in a single thread of execution
 * (explicitly or implicitely), you can use HB_NOLOCK
 *      If the calling module already provide concurrent access protection,
 * you may use HB_NOLOCK.
 *
 *      In all other cases, you need to use HB_LOCK and lock the hashbin
 * every time before calling one of the unprotected calls. You also must
 * use the pointer returned by the unprotected call within the locked
 * region.
 *
 * Extra care for enumeration :
 * --------------------------
 *      hashbin_get_first() and hashbin_get_next() use the hashbin to
 * store the current position, in hb_current.
 *      As long as the hashbin remains locked, this is safe. If you unlock
 * the hashbin, the current position may change if anybody else modify
 * or enumerate the hashbin.
 *      Summary : do the full enumeration while locked.
 *
 *      Alternatively, you may use hashbin_find_next(). But, this will
 * be slower, is more complex to use and doesn't protect the hashbin
 * content. So, care is needed here as well.
 *
 * Other issues :
 * ------------
 *      I believe that we are overdoing it by using spin_lock_irqsave()
 * and we should use only spin_lock_bh() or similar. But, I don't have
 * the balls to try it out.
 *      Don't believe that because hashbin are now (somewhat) SMP safe
 * that the rest of the code is. Higher layers tend to be safest,
 * but LAP and LMP would need some serious dedicated love.
 *
 * Jean II
 */
#include <linux/module.h>

#include <net/irda/irda.h>
#include <net/irda/irqueue.h>

/************************ QUEUE SUBROUTINES ************************/

/*
 * Hashbin
 */
#define GET_HASHBIN(x) ( x & HASHBIN_MASK )

/*
 * Function hash (name)
 *
 *    This function hash the input string 'name' using the ELF hash
 *    function for strings.
 */
static __u32 hash( const char* name)
{
        __u32 h = 0;
        __u32 g;

        while(*name) {
                h = (h<<4) + *name++;
                if ((g = (h & 0xf0000000)))
                        h ^=g>>24;
                h &=~g;
        }
        return h;
}

/*
 * Function enqueue_first (queue, proc)
 *
 *    Insert item first in queue.
 *
 */
static void enqueue_first(irda_queue_t **queue, irda_queue_t* element)
{

        IRDA_DEBUG( 4, "%s()\n", __FUNCTION__);

        /*
         * Check if queue is empty.
         */
        if ( *queue == NULL ) {
                /*
                 * Queue is empty.  Insert one element into the queue.
                 */
                element->q_next = element->q_prev = *queue = element;

        } else {
                /*
                 * Queue is not empty.  Insert element into front of queue.
                 */
                element->q_next          = (*queue);
                (*queue)->q_prev->q_next = element;
                element->q_prev          = (*queue)->q_prev;
                (*queue)->q_prev         = element;
                (*queue)                 = element;
        }
}


/*
 * Function dequeue (queue)
 *
 *    Remove first entry in queue
 *
 */
static irda_queue_t *dequeue_first(irda_queue_t **queue)
{
        irda_queue_t *ret;

        IRDA_DEBUG( 4, "dequeue_first()\n");

        /*
         * Set return value
         */
        ret =  *queue;

        if ( *queue == NULL ) {
                /*
                 * Queue was empty.
                 */
        } else if ( (*queue)->q_next == *queue ) {
                /*
                 *  Queue only contained a single element. It will now be
                 *  empty.
                 */
                *queue = NULL;
        } else {
                /*
                 * Queue contained several element.  Remove the first one.
                 */
                (*queue)->q_prev->q_next = (*queue)->q_next;
                (*queue)->q_next->q_prev = (*queue)->q_prev;
                *queue = (*queue)->q_next;
        }

        /*
         * Return the removed entry (or NULL of queue was empty).
         */
        return ret;
}

/*
 * Function dequeue_general (queue, element)
 *
 *
 */
static irda_queue_t *dequeue_general(irda_queue_t **queue, irda_queue_t* element)
{
        irda_queue_t *ret;

        IRDA_DEBUG( 4, "dequeue_general()\n");

        /*
         * Set return value
         */
        ret =  *queue;

        if ( *queue == NULL ) {
                /*
                 * Queue was empty.
                 */
        } else if ( (*queue)->q_next == *queue ) {
                /*
                 *  Queue only contained a single element. It will now be
                 *  empty.
                 */
                *queue = NULL;

        } else {
                /*
                 *  Remove specific element.
                 */
                element->q_prev->q_next = element->q_next;
                element->q_next->q_prev = element->q_prev;
                if ( (*queue) == element)
                        (*queue) = element->q_next;
        }

        /*
         * Return the removed entry (or NULL of queue was empty).
         */
        return ret;
}

/************************ HASHBIN MANAGEMENT ************************/

/*
 * Function hashbin_create ( type, name )
 *
 *    Create hashbin!
 *
 */
hashbin_t *hashbin_new(int type)
{
        hashbin_t* hashbin;

        /*
         * Allocate new hashbin
         */
        hashbin = kzalloc(sizeof(*hashbin), GFP_ATOMIC);
        if (!hashbin)
                return NULL;

        /*
         * Initialize structure
         */
        hashbin->hb_type = type;
        hashbin->magic = HB_MAGIC;
        //hashbin->hb_current = NULL;

        /* Make sure all spinlock's are unlocked */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_init(&hashbin->hb_spinlock);
        }

        return hashbin;
}
EXPORT_SYMBOL(hashbin_new);


/*
 * Function hashbin_delete (hashbin, free_func)
 *
 *    Destroy hashbin, the free_func can be a user supplied special routine
 *    for deallocating this structure if it's complex. If not the user can
 *    just supply kfree, which should take care of the job.
 */
#ifdef CONFIG_LOCKDEP
static int hashbin_lock_depth = 0;
#endif
int hashbin_delete( hashbin_t* hashbin, FREE_FUNC free_func)
{
        irda_queue_t* queue;
        unsigned long flags = 0;
        int i;

        IRDA_ASSERT(hashbin != NULL, return -1;);
        IRDA_ASSERT(hashbin->magic == HB_MAGIC, return -1;);

        /* Synchronize */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_irqsave_nested(&hashbin->hb_spinlock, flags,
                                         hashbin_lock_depth++);
        }

        /*
         *  Free the entries in the hashbin, TODO: use hashbin_clear when
         *  it has been shown to work
         */
        for (i = 0; i < HASHBIN_SIZE; i ++ ) {
                queue = dequeue_first((irda_queue_t**) &hashbin->hb_queue[i]);
                while (queue ) {
                        if (free_func)
                                (*free_func)(queue);
                        queue = dequeue_first(
                                (irda_queue_t**) &hashbin->hb_queue[i]);
                }
        }

        /* Cleanup local data */
        hashbin->hb_current = NULL;
        hashbin->magic = ~HB_MAGIC;

        /* Release lock */
        if ( hashbin->hb_type & HB_LOCK) {
                spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
#ifdef CONFIG_LOCKDEP
                hashbin_lock_depth--;
#endif
        }

        /*
         *  Free the hashbin structure
         */
        kfree(hashbin);

        return 0;
}
EXPORT_SYMBOL(hashbin_delete);

/********************* HASHBIN LIST OPERATIONS *********************/

/*
 * Function hashbin_insert (hashbin, entry, name)
 *
 *    Insert an entry into the hashbin
 *
 */
void hashbin_insert(hashbin_t* hashbin, irda_queue_t* entry, long hashv,
                    const char* name)
{
        unsigned long flags = 0;
        int bin;

        IRDA_DEBUG( 4, "%s()\n", __FUNCTION__);

        IRDA_ASSERT( hashbin != NULL, return;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return;);

        /*
         * Locate hashbin
         */
        if ( name )
                hashv = hash( name );
        bin = GET_HASHBIN( hashv );

        /* Synchronize */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_irqsave(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        /*
         * Store name and key
         */
        entry->q_hash = hashv;
        if ( name )
                strlcpy( entry->q_name, name, sizeof(entry->q_name));

        /*
         * Insert new entry first
         */
        enqueue_first( (irda_queue_t**) &hashbin->hb_queue[ bin ],
                       entry);
        hashbin->hb_size++;

        /* Release lock */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */
}
EXPORT_SYMBOL(hashbin_insert);

/*
 *  Function hashbin_remove_first (hashbin)
 *
 *    Remove first entry of the hashbin
 *
 * Note : this function no longer use hashbin_remove(), but does things
 * similar to hashbin_remove_this(), so can be considered safe.
 * Jean II
 */
void *hashbin_remove_first( hashbin_t *hashbin)
{
        unsigned long flags = 0;
        irda_queue_t *entry = NULL;

        /* Synchronize */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_irqsave(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        entry = hashbin_get_first( hashbin);
        if ( entry != NULL) {
                int     bin;
                long    hashv;
                /*
                 * Locate hashbin
                 */
                hashv = entry->q_hash;
                bin = GET_HASHBIN( hashv );

                /*
                 * Dequeue the entry...
                 */
                dequeue_general( (irda_queue_t**) &hashbin->hb_queue[ bin ],
                                 (irda_queue_t*) entry );
                hashbin->hb_size--;
                entry->q_next = NULL;
                entry->q_prev = NULL;

                /*
                 *  Check if this item is the currently selected item, and in
                 *  that case we must reset hb_current
                 */
                if ( entry == hashbin->hb_current)
                        hashbin->hb_current = NULL;
        }

        /* Release lock */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        return entry;
}


/*
 *  Function hashbin_remove (hashbin, hashv, name)
 *
 *    Remove entry with the given name
 *
 *  The use of this function is highly discouraged, because the whole
 *  concept behind hashbin_remove() is broken. In many cases, it's not
 *  possible to guarantee the unicity of the index (either hashv or name),
 *  leading to removing the WRONG entry.
 *  The only simple safe use is :
 *              hashbin_remove(hasbin, (int) self, NULL);
 *  In other case, you must think hard to guarantee unicity of the index.
 *  Jean II
 */
void* hashbin_remove( hashbin_t* hashbin, long hashv, const char* name)
{
        int bin, found = FALSE;
        unsigned long flags = 0;
        irda_queue_t* entry;

        IRDA_DEBUG( 4, "%s()\n", __FUNCTION__);

        IRDA_ASSERT( hashbin != NULL, return NULL;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return NULL;);

        /*
         * Locate hashbin
         */
        if ( name )
                hashv = hash( name );
        bin = GET_HASHBIN( hashv );

        /* Synchronize */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_irqsave(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        /*
         * Search for entry
         */
        entry = hashbin->hb_queue[ bin ];
        if ( entry ) {
                do {
                        /*
                         * Check for key
                         */
                        if ( entry->q_hash == hashv ) {
                                /*
                                 * Name compare too?
                                 */
                                if ( name ) {
                                        if ( strcmp( entry->q_name, name) == 0)
                                        {
                                                found = TRUE;
                                                break;
                                        }
                                } else {
                                        found = TRUE;
                                        break;
                                }
                        }
                        entry = entry->q_next;
                } while ( entry != hashbin->hb_queue[ bin ] );
        }

        /*
         * If entry was found, dequeue it
         */
        if ( found ) {
                dequeue_general( (irda_queue_t**) &hashbin->hb_queue[ bin ],
                                 (irda_queue_t*) entry );
                hashbin->hb_size--;

                /*
                 *  Check if this item is the currently selected item, and in
                 *  that case we must reset hb_current
                 */
                if ( entry == hashbin->hb_current)
                        hashbin->hb_current = NULL;
        }

        /* Release lock */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */


        /* Return */
        if ( found )
                return entry;
        else
                return NULL;

}
EXPORT_SYMBOL(hashbin_remove);

/*
 *  Function hashbin_remove_this (hashbin, entry)
 *
 *    Remove entry with the given name
 *
 * In some cases, the user of hashbin can't guarantee the unicity
 * of either the hashv or name.
 * In those cases, using the above function is guaranteed to cause troubles,
 * so we use this one instead...
 * And by the way, it's also faster, because we skip the search phase ;-)
 */
void* hashbin_remove_this( hashbin_t* hashbin, irda_queue_t* entry)
{
        unsigned long flags = 0;
        int     bin;
        long    hashv;

        IRDA_DEBUG( 4, "%s()\n", __FUNCTION__);

        IRDA_ASSERT( hashbin != NULL, return NULL;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return NULL;);
        IRDA_ASSERT( entry != NULL, return NULL;);

        /* Synchronize */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_lock_irqsave(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        /* Check if valid and not already removed... */
        if((entry->q_next == NULL) || (entry->q_prev == NULL)) {
                entry = NULL;
                goto out;
        }

        /*
         * Locate hashbin
         */
        hashv = entry->q_hash;
        bin = GET_HASHBIN( hashv );

        /*
         * Dequeue the entry...
         */
        dequeue_general( (irda_queue_t**) &hashbin->hb_queue[ bin ],
                         (irda_queue_t*) entry );
        hashbin->hb_size--;
        entry->q_next = NULL;
        entry->q_prev = NULL;

        /*
         *  Check if this item is the currently selected item, and in
         *  that case we must reset hb_current
         */
        if ( entry == hashbin->hb_current)
                hashbin->hb_current = NULL;
out:
        /* Release lock */
        if ( hashbin->hb_type & HB_LOCK ) {
                spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);
        } /* Default is no-lock  */

        return entry;
}
EXPORT_SYMBOL(hashbin_remove_this);

/*********************** HASHBIN ENUMERATION ***********************/

/*
 * Function hashbin_common_find (hashbin, hashv, name)
 *
 *    Find item with the given hashv or name
 *
 */
void* hashbin_find( hashbin_t* hashbin, long hashv, const char* name )
{
        int bin;
        irda_queue_t* entry;

        IRDA_DEBUG( 4, "hashbin_find()\n");

        IRDA_ASSERT( hashbin != NULL, return NULL;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return NULL;);

        /*
         * Locate hashbin
         */
        if ( name )
                hashv = hash( name );
        bin = GET_HASHBIN( hashv );

        /*
         * Search for entry
         */
        entry = hashbin->hb_queue[ bin];
        if ( entry ) {
                do {
                        /*
                         * Check for key
                         */
                        if ( entry->q_hash == hashv ) {
                                /*
                                 * Name compare too?
                                 */
                                if ( name ) {
                                        if ( strcmp( entry->q_name, name ) == 0 ) {
                                                return entry;
                                        }
                                } else {
                                        return entry;
                                }
                        }
                        entry = entry->q_next;
                } while ( entry != hashbin->hb_queue[ bin ] );
        }

        return NULL;
}
EXPORT_SYMBOL(hashbin_find);

/*
 * Function hashbin_lock_find (hashbin, hashv, name)
 *
 *    Find item with the given hashv or name
 *
 * Same, but with spinlock protection...
 * I call it safe, but it's only safe with respect to the hashbin, not its
 * content. - Jean II
 */
void* hashbin_lock_find( hashbin_t* hashbin, long hashv, const char* name )
{
        unsigned long flags = 0;
        irda_queue_t* entry;

        /* Synchronize */
        spin_lock_irqsave(&hashbin->hb_spinlock, flags);

        /*
         * Search for entry
         */
        entry = (irda_queue_t* ) hashbin_find( hashbin, hashv, name );

        /* Release lock */
        spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);

        return entry;
}
EXPORT_SYMBOL(hashbin_lock_find);

/*
 * Function hashbin_find (hashbin, hashv, name, pnext)
 *
 *    Find an item with the given hashv or name, and its successor
 *
 * This function allow to do concurrent enumerations without the
 * need to lock over the whole session, because the caller keep the
 * context of the search. On the other hand, it might fail and return
 * NULL if the entry is removed. - Jean II
 */
void* hashbin_find_next( hashbin_t* hashbin, long hashv, const char* name,
                         void ** pnext)
{
        unsigned long flags = 0;
        irda_queue_t* entry;

        /* Synchronize */
        spin_lock_irqsave(&hashbin->hb_spinlock, flags);

        /*
         * Search for current entry
         * This allow to check if the current item is still in the
         * hashbin or has been removed.
         */
        entry = (irda_queue_t* ) hashbin_find( hashbin, hashv, name );

        /*
         * Trick hashbin_get_next() to return what we want
         */
        if(entry) {
                hashbin->hb_current = entry;
                *pnext = hashbin_get_next( hashbin );
        } else
                *pnext = NULL;

        /* Release lock */
        spin_unlock_irqrestore(&hashbin->hb_spinlock, flags);

        return entry;
}

/*
 * Function hashbin_get_first (hashbin)
 *
 *    Get a pointer to first element in hashbin, this function must be
 *    called before any calls to hashbin_get_next()!
 *
 */
irda_queue_t *hashbin_get_first( hashbin_t* hashbin)
{
        irda_queue_t *entry;
        int i;

        IRDA_ASSERT( hashbin != NULL, return NULL;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return NULL;);

        if ( hashbin == NULL)
                return NULL;

        for ( i = 0; i < HASHBIN_SIZE; i ++ ) {
                entry = hashbin->hb_queue[ i];
                if ( entry) {
                        hashbin->hb_current = entry;
                        return entry;
                }
        }
        /*
         *  Did not find any item in hashbin
         */
        return NULL;
}
EXPORT_SYMBOL(hashbin_get_first);

/*
 * Function hashbin_get_next (hashbin)
 *
 *    Get next item in hashbin. A series of hashbin_get_next() calls must
 *    be started by a call to hashbin_get_first(). The function returns
 *    NULL when all items have been traversed
 *
 * The context of the search is stored within the hashbin, so you must
 * protect yourself from concurrent enumerations. - Jean II
 */
irda_queue_t *hashbin_get_next( hashbin_t *hashbin)
{
        irda_queue_t* entry;
        int bin;
        int i;

        IRDA_ASSERT( hashbin != NULL, return NULL;);
        IRDA_ASSERT( hashbin->magic == HB_MAGIC, return NULL;);

        if ( hashbin->hb_current == NULL) {
                IRDA_ASSERT( hashbin->hb_current != NULL, return NULL;);
                return NULL;
        }
        entry = hashbin->hb_current->q_next;
        bin = GET_HASHBIN( entry->q_hash);

        /*
         *  Make sure that we are not back at the beginning of the queue
         *  again
         */
        if ( entry != hashbin->hb_queue[ bin ]) {
                hashbin->hb_current = entry;

                return entry;
        }

        /*
         *  Check that this is not the last queue in hashbin
         */
        if ( bin >= HASHBIN_SIZE)
                return NULL;

        /*
         *  Move to next queue in hashbin
         */
        bin++;
        for ( i = bin; i < HASHBIN_SIZE; i++ ) {
                entry = hashbin->hb_queue[ i];
                if ( entry) {
                        hashbin->hb_current = entry;

                        return entry;
                }
        }
        return NULL;
}
EXPORT_SYMBOL(hashbin_get_next);