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|
/*********************************************************************
*
* 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(
|