/********************************************************************* * * 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", __func__); /* * 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", __func__); 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", __func__); 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", __func__); 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);