1/*
2 * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
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27 */
28/*
29 * @OSF_COPYRIGHT@
30 */
31/*
32 * Mach Operating System
33 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
34 * All Rights Reserved.
35 *
36 * Permission to use, copy, modify and distribute this software and its
37 * documentation is hereby granted, provided that both the copyright
38 * notice and this permission notice appear in all copies of the
39 * software, derivative works or modified versions, and any portions
40 * thereof, and that both notices appear in supporting documentation.
41 *
42 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
43 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
44 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
45 *
46 * Carnegie Mellon requests users of this software to return to
47 *
48 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
49 *  School of Computer Science
50 *  Carnegie Mellon University
51 *  Pittsburgh PA 15213-3890
52 *
53 * any improvements or extensions that they make and grant Carnegie Mellon
54 * the rights to redistribute these changes.
55 */
56/*
57 */
58/*
59 *	File:	ipc/ipc_hash.c
60 *	Author:	Rich Draves
61 *	Date:	1989
62 *
63 *	Entry hash table operations.
64 */
65
66#include <mach/boolean.h>
67#include <mach/port.h>
68#include <kern/kalloc.h>
69#include <ipc/port.h>
70#include <ipc/ipc_space.h>
71#include <ipc/ipc_object.h>
72#include <ipc/ipc_entry.h>
73#include <ipc/ipc_hash.h>
74#include <ipc/ipc_init.h>
75
76#include <mach_ipc_debug.h>
77
78#if	MACH_IPC_DEBUG
79#include <mach/kern_return.h>
80#include <mach_debug/hash_info.h>
81#include <vm/vm_map.h>
82#include <vm/vm_kern.h>
83#endif	/* MACH_IPC_DEBUG */
84
85/*
86 * Forward declarations
87 */
88
89/* Delete an entry from the local reverse hash table */
90void ipc_hash_local_delete(
91	ipc_space_t		space,
92	ipc_object_t		obj,
93	mach_port_index_t	index,
94	ipc_entry_t		entry);
95
96/*
97 *	Routine:	ipc_hash_lookup
98 *	Purpose:
99 *		Converts (space, obj) -> (name, entry).
100 *		Returns TRUE if an entry was found.
101 *	Conditions:
102 *		The space must be locked (read or write) throughout.
103 */
104
105boolean_t
106ipc_hash_lookup(
107	ipc_space_t		space,
108	ipc_object_t		obj,
109	mach_port_name_t	*namep,
110	ipc_entry_t		*entryp)
111{
112	return ipc_hash_table_lookup(space->is_table, space->is_table_size, obj, namep, entryp);
113}
114
115/*
116 *	Routine:	ipc_hash_insert
117 *	Purpose:
118 *		Inserts an entry into the appropriate reverse hash table,
119 *		so that ipc_hash_lookup will find it.
120 *	Conditions:
121 *		The space must be write-locked.
122 */
123
124void
125ipc_hash_insert(
126	ipc_space_t		space,
127	ipc_object_t		obj,
128	mach_port_name_t	name,
129	ipc_entry_t		entry)
130{
131	mach_port_index_t index;
132
133	index = MACH_PORT_INDEX(name);
134	ipc_hash_table_insert(space->is_table, space->is_table_size, obj, index, entry);
135}
136
137/*
138 *	Routine:	ipc_hash_delete
139 *	Purpose:
140 *		Deletes an entry from the appropriate reverse hash table.
141 *	Conditions:
142 *		The space must be write-locked.
143 */
144
145void
146ipc_hash_delete(
147	ipc_space_t		space,
148	ipc_object_t		obj,
149	mach_port_name_t	name,
150	ipc_entry_t		entry)
151{
152	mach_port_index_t index;
153
154	index = MACH_PORT_INDEX(name);
155	ipc_hash_table_delete(space->is_table, space->is_table_size, obj, index, entry);
156}
157
158/*
159 *	Each space has a local reverse hash table, which holds
160 *	entries from the space's table.  In fact, the hash table
161 *	just uses a field (ie_index) in the table itself.
162 *
163 *	The local hash table is an open-addressing hash table,
164 *	which means that when a collision occurs, instead of
165 *	throwing the entry into a bucket, the entry is rehashed
166 *	to another position in the table.  In this case the rehash
167 *	is very simple: linear probing (ie, just increment the position).
168 *	This simple rehash makes deletions tractable (they're still a pain),
169 *	but it means that collisions tend to build up into clumps.
170 *
171 *	Because at least one entry in the table (index 0) is always unused,
172 *	there will always be room in the reverse hash table.  If a table
173 *	with n slots gets completely full, the reverse hash table will
174 *	have one giant clump of n-1 slots and one free slot somewhere.
175 *	Because entries are only entered into the reverse table if they
176 *	are pure send rights (not receive, send-once, port-set,
177 *	or dead-name rights), and free entries of course aren't entered,
178 *	I expect the reverse hash table won't get unreasonably full.
179 *
180 *	Ordered hash tables (Amble & Knuth, Computer Journal, v. 17, no. 2,
181 *	pp. 135-142.) may be desirable here.  They can dramatically help
182 *	unsuccessful lookups.  But unsuccessful lookups are almost always
183 *	followed by insertions, and those slow down somewhat.  They
184 *	also can help deletions somewhat.  Successful lookups aren't affected.
185 *	So possibly a small win; probably nothing significant.
186 */
187
188#define	IH_TABLE_HASH(obj, size)				\
189		((mach_port_index_t)((((uintptr_t) (obj)) >> 6) % (size)))
190
191/*
192 *	Routine:	ipc_hash_table_lookup
193 *	Purpose:
194 *		Converts (table, obj) -> (name, entry).
195 *	Conditions:
196 *		Must have read consistency on the table.
197 */
198
199boolean_t
200ipc_hash_table_lookup(
201	ipc_entry_t		table,
202	ipc_entry_num_t		size,
203	ipc_object_t		obj,
204	mach_port_name_t	*namep,
205	ipc_entry_t		*entryp)
206{
207	mach_port_index_t hindex, index;
208
209	if (obj == IO_NULL) {
210		return FALSE;
211	}
212
213	hindex = IH_TABLE_HASH(obj, size);
214
215	/*
216	 *	Ideally, table[hindex].ie_index is the name we want.
217	 *	However, must check ie_object to verify this,
218	 *	because collisions can happen.  In case of a collision,
219	 *	search farther along in the clump.
220	 */
221
222	while ((index = table[hindex].ie_index) != 0) {
223		ipc_entry_t entry;
224
225		assert(index < size);
226		entry = &table[index];
227		if (entry->ie_object == obj) {
228			*entryp = entry;
229			*namep = MACH_PORT_MAKE(index,
230						IE_BITS_GEN(entry->ie_bits));
231			return TRUE;
232		}
233
234		if (++hindex == size)
235			hindex = 0;
236	}
237
238	return FALSE;
239}
240
241/*
242 *	Routine:	ipc_hash_table_insert
243 *	Purpose:
244 *		Inserts an entry into the space's reverse hash table.
245 *	Conditions:
246 *		The space must be write-locked.
247 */
248
249void
250ipc_hash_table_insert(
251	ipc_entry_t			table,
252	ipc_entry_num_t			size,
253	ipc_object_t			obj,
254	mach_port_index_t		index,
255	__assert_only ipc_entry_t	entry)
256{
257	mach_port_index_t hindex;
258
259	assert(index != 0);
260	assert(obj != IO_NULL);
261
262	hindex = IH_TABLE_HASH(obj, size);
263
264	assert(entry == &table[index]);
265	assert(entry->ie_object == obj);
266
267	/*
268	 *	We want to insert at hindex, but there may be collisions.
269	 *	If a collision occurs, search for the end of the clump
270	 *	and insert there.
271	 */
272
273	while (table[hindex].ie_index != 0) {
274		if (++hindex == size)
275			hindex = 0;
276	}
277
278	table[hindex].ie_index = index;
279}
280
281/*
282 *	Routine:	ipc_hash_table_delete
283 *	Purpose:
284 *		Deletes an entry from the table's reverse hash.
285 *	Conditions:
286 *		Exclusive access to the table.
287 */
288
289void
290ipc_hash_table_delete(
291	ipc_entry_t			table,
292	ipc_entry_num_t			size,
293	ipc_object_t			obj,
294	mach_port_index_t		index,
295	__assert_only ipc_entry_t	entry)
296{
297	mach_port_index_t hindex, dindex;
298
299	assert(index != MACH_PORT_NULL);
300	assert(obj != IO_NULL);
301
302	hindex = IH_TABLE_HASH(obj, size);
303
304	assert(entry == &table[index]);
305	assert(entry->ie_object == obj);
306
307	/*
308	 *	First check we have the right hindex for this index.
309	 *	In case of collision, we have to search farther
310	 *	along in this clump.
311	 */
312
313	while (table[hindex].ie_index != index) {
314		if (++hindex == size)
315			hindex = 0;
316	}
317
318	/*
319	 *	Now we want to set table[hindex].ie_index = 0.
320	 *	But if we aren't the last index in a clump,
321	 *	this might cause problems for lookups of objects
322	 *	farther along in the clump that are displaced
323	 *	due to collisions.  Searches for them would fail
324	 *	at hindex instead of succeeding.
325	 *
326	 *	So we must check the clump after hindex for objects
327	 *	that are so displaced, and move one up to the new hole.
328	 *
329	 *		hindex - index of new hole in the clump
330	 *		dindex - index we are checking for a displaced object
331	 *
332	 *	When we move a displaced object up into the hole,
333	 *	it creates a new hole, and we have to repeat the process
334	 *	until we get to the end of the clump.
335	 */
336
337	for (dindex = hindex; index != 0; hindex = dindex) {
338		for (;;) {
339			mach_port_index_t tindex;
340			ipc_object_t tobj;
341
342			if (++dindex == size)
343				dindex = 0;
344			assert(dindex != hindex);
345
346			/* are we at the end of the clump? */
347
348			index = table[dindex].ie_index;
349			if (index == 0)
350				break;
351
352			/* is this a displaced object? */
353
354			tobj = table[index].ie_object;
355			assert(tobj != IO_NULL);
356			tindex = IH_TABLE_HASH(tobj, size);
357
358			if ((dindex < hindex) ?
359			    ((dindex < tindex) && (tindex <= hindex)) :
360			    ((dindex < tindex) || (tindex <= hindex)))
361				break;
362		}
363
364		table[hindex].ie_index = index;
365	}
366}
367
368