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[apple/xnu.git] / osfmk / ipc / ipc_hash.c

/*
 * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
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 * Please see the License for the specific language governing rights and
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 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   ipc/ipc_hash.c
 *      Author: Rich Draves
 *      Date:   1989
 *
 *      Entry hash table operations.
 */

#include <mach/boolean.h>
#include <mach/port.h>
#include <kern/lock.h>
#include <kern/kalloc.h>
#include <ipc/port.h>
#include <ipc/ipc_space.h>
#include <ipc/ipc_object.h>
#include <ipc/ipc_entry.h>
#include <ipc/ipc_hash.h>
#include <ipc/ipc_init.h>

#include <mach_ipc_debug.h>

#if     MACH_IPC_DEBUG
#include <mach/kern_return.h>
#include <mach_debug/hash_info.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#endif  /* MACH_IPC_DEBUG */

/*
 * Forward declarations 
 */

/* Lookup (space, obj) in global hash table */
boolean_t ipc_hash_global_lookup(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        *namep,
        ipc_tree_entry_t        *entryp);

/* Insert an entry into the global reverse hash table */
void ipc_hash_global_insert(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        name,
        ipc_tree_entry_t        entry);

/* Delete an entry from the local reverse hash table */
void ipc_hash_local_delete(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_index_t       index,
        ipc_entry_t             entry);

/*
 *      Routine:        ipc_hash_lookup
 *      Purpose:
 *              Converts (space, obj) -> (name, entry).
 *              Returns TRUE if an entry was found.
 *      Conditions:
 *              The space must be locked (read or write) throughout.
 */

boolean_t
ipc_hash_lookup(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        *namep,
        ipc_entry_t             *entryp)
{
        boolean_t       rv;

        rv = ipc_hash_local_lookup(space, obj, namep, entryp);
        if (!rv) {
                assert(!is_fast_space(space) || space->is_tree_hash == 0);
                if (space->is_tree_hash > 0)
                        rv = ipc_hash_global_lookup(space, obj, namep,
                                (ipc_tree_entry_t *) entryp);
        }
        return (rv);
}

/*
 *      Routine:        ipc_hash_insert
 *      Purpose:
 *              Inserts an entry into the appropriate reverse hash table,
 *              so that ipc_hash_lookup will find it.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_insert(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        name,
        ipc_entry_t             entry)
{
        mach_port_index_t index;

        index = MACH_PORT_INDEX(name);
        if ((index < space->is_table_size) &&
            (entry == &space->is_table[index]))
                ipc_hash_local_insert(space, obj, index, entry);
        else {
                assert(!is_fast_space(space));
                ipc_hash_global_insert(space, obj, name,
                                       (ipc_tree_entry_t) entry);
        }
}

/*
 *      Routine:        ipc_hash_delete
 *      Purpose:
 *              Deletes an entry from the appropriate reverse hash table.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_delete(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        name,
        ipc_entry_t             entry)
{
        mach_port_index_t index;

        index = MACH_PORT_INDEX(name);
        if ((index < space->is_table_size) &&
            (entry == &space->is_table[index]))
                ipc_hash_local_delete(space, obj, index, entry);
        else {
                assert(!is_fast_space(space));
                ipc_hash_global_delete(space, obj, name,
                                       (ipc_tree_entry_t) entry);
        }
}

/*
 *      The global reverse hash table holds splay tree entries.
 *      It is a simple open-chaining hash table with singly-linked buckets.
 *      Each bucket is locked separately, with an exclusive lock.
 *      Within each bucket, move-to-front is used.
 */

typedef natural_t ipc_hash_index_t;

ipc_hash_index_t ipc_hash_global_size;
ipc_hash_index_t ipc_hash_global_mask;

#define IH_GLOBAL_HASH(space, obj)                                      \
        (((((ipc_hash_index_t) ((vm_offset_t)space)) >> 4) +            \
          (((ipc_hash_index_t) ((vm_offset_t)obj)) >> 6)) &             \
         ipc_hash_global_mask)

typedef struct ipc_hash_global_bucket {
        decl_mutex_data(,       ihgb_lock_data)
        ipc_tree_entry_t        ihgb_head;
} *ipc_hash_global_bucket_t;

#define IHGB_NULL       ((ipc_hash_global_bucket_t) 0)

#define ihgb_lock_init(ihgb)    mutex_init(&(ihgb)->ihgb_lock_data, 0)
#define ihgb_lock(ihgb)         mutex_lock(&(ihgb)->ihgb_lock_data)
#define ihgb_unlock(ihgb)       mutex_unlock(&(ihgb)->ihgb_lock_data)

ipc_hash_global_bucket_t ipc_hash_global_table;

/*
 *      Routine:        ipc_hash_global_lookup
 *      Purpose:
 *              Converts (space, obj) -> (name, entry).
 *              Looks in the global table, for splay tree entries.
 *              Returns TRUE if an entry was found.
 *      Conditions:
 *              The space must be locked (read or write) throughout.
 */

boolean_t
ipc_hash_global_lookup(
        ipc_space_t                     space,
        ipc_object_t                    obj,
        mach_port_name_t                *namep,
        ipc_tree_entry_t                *entryp)
{
        ipc_hash_global_bucket_t bucket;
        ipc_tree_entry_t this, *last;

        assert(space != IS_NULL);
        assert(obj != IO_NULL);

        assert(!is_fast_space(space));
        bucket = &ipc_hash_global_table[IH_GLOBAL_HASH(space, obj)];
        ihgb_lock(bucket);

        if ((this = bucket->ihgb_head) != ITE_NULL) {
                if ((this->ite_object == obj) &&
                    (this->ite_space == space)) {
                        /* found it at front; no need to move */

                        *namep = this->ite_name;
                        *entryp = this;
                } else for (last = &this->ite_next;
                            (this = *last) != ITE_NULL;
                            last = &this->ite_next) {
                        if ((this->ite_object == obj) &&
                            (this->ite_space == space)) {
                                /* found it; move to front */

                                *last = this->ite_next;
                                this->ite_next = bucket->ihgb_head;
                                bucket->ihgb_head = this;

                                *namep = this->ite_name;
                                *entryp = this;
                                break;
                        }
                }
        }

        ihgb_unlock(bucket);
        return this != ITE_NULL;
}

/*
 *      Routine:        ipc_hash_global_insert
 *      Purpose:
 *              Inserts an entry into the global reverse hash table.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_global_insert(
        ipc_space_t                             space,
        ipc_object_t                            obj,
        __assert_only mach_port_name_t  name,
        ipc_tree_entry_t                        entry)
{
        ipc_hash_global_bucket_t bucket;

        assert(!is_fast_space(space));
        assert(entry->ite_name == name);
        assert(space != IS_NULL);
        assert(entry->ite_space == space);
        assert(obj != IO_NULL);
        assert(entry->ite_object == obj);

        space->is_tree_hash++;
        assert(space->is_tree_hash <= space->is_tree_total);

        bucket = &ipc_hash_global_table[IH_GLOBAL_HASH(space, obj)];
        ihgb_lock(bucket);

        /* insert at front of bucket */

        entry->ite_next = bucket->ihgb_head;
        bucket->ihgb_head = entry;

        ihgb_unlock(bucket);
}

/*
 *      Routine:        ipc_hash_global_delete
 *      Purpose:
 *              Deletes an entry from the global reverse hash table.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_global_delete(
        ipc_space_t                             space,
        ipc_object_t                            obj,
        __assert_only mach_port_name_t  name,
        ipc_tree_entry_t                        entry)
{
        ipc_hash_global_bucket_t bucket;
        ipc_tree_entry_t this, *last;

        assert(!is_fast_space(space));
        assert(entry->ite_name == name);
        assert(space != IS_NULL);
        assert(entry->ite_space == space);
        assert(obj != IO_NULL);
        assert(entry->ite_object == obj);

        assert(space->is_tree_hash > 0);
        space->is_tree_hash--;

        bucket = &ipc_hash_global_table[IH_GLOBAL_HASH(space, obj)];
        ihgb_lock(bucket);

        for (last = &bucket->ihgb_head;
             (this = *last) != ITE_NULL;
             last = &this->ite_next) {
                if (this == entry) {
                        /* found it; remove from bucket */

                        *last = this->ite_next;
                        break;
                }
        }
        assert(this != ITE_NULL);

        ihgb_unlock(bucket);
}

/*
 *      Each space has a local reverse hash table, which holds
 *      entries from the space's table.  In fact, the hash table
 *      just uses a field (ie_index) in the table itself.
 *
 *      The local hash table is an open-addressing hash table,
 *      which means that when a collision occurs, instead of
 *      throwing the entry into a bucket, the entry is rehashed
 *      to another position in the table.  In this case the rehash
 *      is very simple: linear probing (ie, just increment the position).
 *      This simple rehash makes deletions tractable (they're still a pain),
 *      but it means that collisions tend to build up into clumps.
 *
 *      Because at least one entry in the table (index 0) is always unused,
 *      there will always be room in the reverse hash table.  If a table
 *      with n slots gets completely full, the reverse hash table will
 *      have one giant clump of n-1 slots and one free slot somewhere.
 *      Because entries are only entered into the reverse table if they
 *      are pure send rights (not receive, send-once, port-set,
 *      or dead-name rights), and free entries of course aren't entered,
 *      I expect the reverse hash table won't get unreasonably full.
 *
 *      Ordered hash tables (Amble & Knuth, Computer Journal, v. 17, no. 2,
 *      pp. 135-142.) may be desirable here.  They can dramatically help
 *      unsuccessful lookups.  But unsuccessful lookups are almost always
 *      followed by insertions, and those slow down somewhat.  They
 *      also can help deletions somewhat.  Successful lookups aren't affected.
 *      So possibly a small win; probably nothing significant.
 */

#define IH_LOCAL_HASH(obj, size)                                \
                ((((mach_port_index_t) (obj)) >> 6) % (size))

/*
 *      Routine:        ipc_hash_local_lookup
 *      Purpose:
 *              Converts (space, obj) -> (name, entry).
 *              Looks in the space's local table, for table entries.
 *              Returns TRUE if an entry was found.
 *      Conditions:
 *              The space must be locked (read or write) throughout.
 */

boolean_t
ipc_hash_local_lookup(
        ipc_space_t             space,
        ipc_object_t            obj,
        mach_port_name_t        *namep,
        ipc_entry_t             *entryp)
{
        ipc_entry_t table;
        ipc_entry_num_t size;
        mach_port_index_t hindex, index;

        assert(space != IS_NULL);
        assert(obj != IO_NULL);

        table = space->is_table;
        size = space->is_table_size;
        hindex = IH_LOCAL_HASH(obj, size);

        /*
         *      Ideally, table[hindex].ie_index is the name we want.
         *      However, must check ie_object to verify this,
         *      because collisions can happen.  In case of a collision,
         *      search farther along in the clump.
         */

        while ((index = table[hindex].ie_index) != 0) {
                ipc_entry_t entry = &table[index];

                if (entry->ie_object == obj) {
                        *entryp = entry;
                        *namep = MACH_PORT_MAKE(index,
                                                IE_BITS_GEN(entry->ie_bits));
                        return TRUE;
                }

                if (++hindex == size)
                        hindex = 0;
        }

        return FALSE;
}

/*
 *      Routine:        ipc_hash_local_insert
 *      Purpose:
 *              Inserts an entry into the space's reverse hash table.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_local_insert(
        ipc_space_t                     space,
        ipc_object_t                    obj,
        mach_port_index_t               index,
        __assert_only ipc_entry_t       entry)
{
        ipc_entry_t table;
        ipc_entry_num_t size;
        mach_port_index_t hindex;

        assert(index != 0);
        assert(space != IS_NULL);
        assert(obj != IO_NULL);

        table = space->is_table;
        size = space->is_table_size;
        hindex = IH_LOCAL_HASH(obj, size);

        assert(entry == &table[index]);
        assert(entry->ie_object == obj);

        /*
         *      We want to insert at hindex, but there may be collisions.
         *      If a collision occurs, search for the end of the clump
         *      and insert there.
         */

        while (table[hindex].ie_index != 0) {
                if (++hindex == size)
                        hindex = 0;
        }

        table[hindex].ie_index = index;
}

/*
 *      Routine:        ipc_hash_local_delete
 *      Purpose:
 *              Deletes an entry from the space's reverse hash table.
 *      Conditions:
 *              The space must be write-locked.
 */

void
ipc_hash_local_delete(
        ipc_space_t                     space,
        ipc_object_t                    obj,
        mach_port_index_t               index,
        __assert_only ipc_entry_t       entry)
{
        ipc_entry_t table;
        ipc_entry_num_t size;
        mach_port_index_t hindex, dindex;

        assert(index != MACH_PORT_NULL);
        assert(space != IS_NULL);
        assert(obj != IO_NULL);

        table = space->is_table;
        size = space->is_table_size;
        hindex = IH_LOCAL_HASH(obj, size);

        assert(entry == &table[index]);
        assert(entry->ie_object == obj);

        /*
         *      First check we have the right hindex for this index.
         *      In case of collision, we have to search farther
         *      along in this clump.
         */

        while (table[hindex].ie_index != index) {
                if (++hindex == size)
                        hindex = 0;
        }

        /*
         *      Now we want to set table[hindex].ie_index = 0.
         *      But if we aren't the last index in a clump,
         *      this might cause problems for lookups of objects
         *      farther along in the clump that are displaced
         *      due to collisions.  Searches for them would fail
         *      at hindex instead of succeeding.
         *
         *      So we must check the clump after hindex for objects
         *      that are so displaced, and move one up to the new hole.
         *
         *              hindex - index of new hole in the clump
         *              dindex - index we are checking for a displaced object
         *
         *      When we move a displaced object up into the hole,
         *      it creates a new hole, and we have to repeat the process
         *      until we get to the end of the clump.
         */

        for (dindex = hindex; index != 0; hindex = dindex) {
                for (;;) {
                        mach_port_index_t tindex;
                        ipc_object_t tobj;

                        if (++dindex == size)
                                dindex = 0;
                        assert(dindex != hindex);

                        /* are we at the end of the clump? */

                        index = table[dindex].ie_index;
                        if (index == 0)
                                break;

                        /* is this a displaced object? */

                        tobj = table[index].ie_object;
                        assert(tobj != IO_NULL);
                        tindex = IH_LOCAL_HASH(tobj, size);

                        if ((dindex < hindex) ?
                            ((dindex < tindex) && (tindex <= hindex)) :
                            ((dindex < tindex) || (tindex <= hindex)))
                                break;
                }

                table[hindex].ie_index = index;
        }
}

/*
 *      Routine:        ipc_hash_init
 *      Purpose:
 *              Initialize the reverse hash table implementation.
 */

void
ipc_hash_init(void)
{
        ipc_hash_index_t i;

        /* if not configured, initialize ipc_hash_global_size */

        if (ipc_hash_global_size == 0) {
                ipc_hash_global_size = ipc_tree_entry_max >> 8;
                if (ipc_hash_global_size < 32)
                        ipc_hash_global_size = 32;
        }

        /* make sure it is a power of two */

        ipc_hash_global_mask = ipc_hash_global_size - 1;
        if ((ipc_hash_global_size & ipc_hash_global_mask) != 0) {
                natural_t bit;

                /* round up to closest power of two */

                for (bit = 1;; bit <<= 1) {
                        ipc_hash_global_mask |= bit;
                        ipc_hash_global_size = ipc_hash_global_mask + 1;

                        if ((ipc_hash_global_size & ipc_hash_global_mask) == 0)
                                break;
                }
        }

        /* allocate ipc_hash_global_table */

        ipc_hash_global_table = (ipc_hash_global_bucket_t)
                kalloc((vm_size_t) (ipc_hash_global_size *
                                    sizeof(struct ipc_hash_global_bucket)));
        assert(ipc_hash_global_table != IHGB_NULL);

        /* and initialize it */

        for (i = 0; i < ipc_hash_global_size; i++) {
                ipc_hash_global_bucket_t bucket;

                bucket = &ipc_hash_global_table[i];
                ihgb_lock_init(bucket);
                bucket->ihgb_head = ITE_NULL;
        }
}

#if     MACH_IPC_DEBUG

/*
 *      Routine:        ipc_hash_info
 *      Purpose:
 *              Return information about the global reverse hash table.
 *              Fills the buffer with as much information as possible
 *              and returns the desired size of the buffer.
 *      Conditions:
 *              Nothing locked.  The caller should provide
 *              possibly-pageable memory.
 */


ipc_hash_index_t
ipc_hash_info(
        hash_info_bucket_t      *info,
        mach_msg_type_number_t count)
{
        ipc_hash_index_t i;

        if (ipc_hash_global_size < count)
                count = ipc_hash_global_size;

        for (i = 0; i < count; i++) {
                ipc_hash_global_bucket_t bucket = &ipc_hash_global_table[i];
                unsigned int bucket_count = 0;
                ipc_tree_entry_t entry;

                ihgb_lock(bucket);
                for (entry = bucket->ihgb_head;
                     entry != ITE_NULL;
                     entry = entry->ite_next)
                        bucket_count++;
                ihgb_unlock(bucket);

                /* don't touch pageable memory while holding locks */
                info[i].hib_count = bucket_count;
        }

        return ipc_hash_global_size;
}

#endif  /* MACH_IPC_DEBUG */