thttpd/mmc.c

/* mmc.c - mmap cache
**
** Copyright © 1998,2001 by Jef Poskanzer <jef@acme.com>.
** All rights reserved.
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions
** are met:
** 1. Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
** 2. Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in the
**    documentation and/or other materials provided with the distribution.
**
** THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
** ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
** FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
** DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
** OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
** HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
** OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
** SUCH DAMAGE.
*/

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <syslog.h>

#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif /* HAVE_MMAP */

#include "mmc.h"


/* Defines. */
#ifndef DEFAULT_EXPIRE_AGE
#define DEFAULT_EXPIRE_AGE 600
#endif
#ifndef DESIRED_FREE_COUNT
#define DESIRED_FREE_COUNT 100
#endif
#ifndef DESIRED_MAX_MAPPED_FILES
#define DESIRED_MAX_MAPPED_FILES 2000
#endif
#ifndef INITIAL_HASH_SIZE
#define INITIAL_HASH_SIZE (1 << 10)
#endif

#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))


/* The Map struct. */
typedef struct MapStruct {
    ino_t ino;
    dev_t dev;
    off_t size;
    time_t ctime;
    int refcount;
    time_t reftime;
    void* addr;
    unsigned int hash;
    int hash_idx;
    struct MapStruct* next;
    } Map;


/* Globals. */
static Map* maps = (Map*) 0;
static Map* free_maps = (Map*) 0;
static int alloc_count = 0, map_count = 0, free_count = 0;
static Map** hash_table = (Map**) 0;
static int hash_size;
static unsigned int hash_mask;
static time_t expire_age = DEFAULT_EXPIRE_AGE;


/* Forwards. */
static void really_unmap( Map** mm );
static int check_hash_size( void );
static int add_hash( Map* m );
static Map* find_hash( ino_t ino, dev_t dev, off_t size, time_t ctime );
static unsigned int hash( ino_t ino, dev_t dev, off_t size, time_t ctime );


void*
mmc_map( char* filename, struct stat* sbP, struct timeval* nowP )
    {
    time_t now;
    struct stat sb;
    Map* m;
    int fd;

    /* Stat the file, if necessary. */
    if ( sbP != (struct stat*) 0 )
        sb = *sbP;
    else
        {
        if ( stat( filename, &sb ) != 0 )
            {
            syslog( LOG_ERR, "stat - %m" );
            return (void*) 0;
            }
        }

    /* Get the current time, if necessary. */
    if ( nowP != (struct timeval*) 0 )
        now = nowP->tv_sec;
    else
        now = time( (time_t*) 0 );

    /* See if we have it mapped already, via the hash table. */
    if ( check_hash_size() < 0 )
        {
        syslog( LOG_ERR, "check_hash_size() failure" );
        return (void*) 0;
        }
    m = find_hash( sb.st_ino, sb.st_dev, sb.st_size, sb.st_ctime );
    if ( m != (Map*) 0 )
        {
        /* Yep.  Just return the existing map */
        ++m->refcount;
        m->reftime = now;
        return m->addr;
        }

    /* Open the file. */
    fd = open( filename, O_RDONLY );
    if ( fd < 0 )
        {
        syslog( LOG_ERR, "open - %m" );
        return (void*) 0;
        }

    /* Find a free Map entry or make a new one. */
    if ( free_maps != (Map*) 0 )
        {
        m = free_maps;
        free_maps = m->next;
        --free_count;
        }
    else
        {
        m = (Map*) malloc( sizeof(Map) );
        if ( m == (Map*) 0 )
            {
            (void) close( fd );
            syslog( LOG_ERR, "out of memory allocating a Map" );
            return (void*) 0;
            }
        ++alloc_count;
        }

    /* Fill in the Map entry. */
    m->ino = sb.st_ino;
    m->dev = sb.st_dev;
    m->size = sb.st_size;
    m->ctime = sb.st_ctime;
    m->refcount = 1;
    m->reftime = now;

    /* Avoid doing anything for zero-length files; some systems don't like
    ** to mmap them, other systems dislike mallocing zero bytes.
    */
    if ( m->size == 0 )
        m->addr = (void*) 1;    /* arbitrary non-NULL address */
    else
        {
#ifdef HAVE_MMAP
        /* Map the file into memory. */
        m->addr = mmap( 0, m->size, PROT_READ, MAP_SHARED, fd, 0 );
        if ( m->addr == (void*) -1 )
            {
            syslog( LOG_ERR, "mmap - %m" );
            (void) close( fd );
            free( (void*) m );
            --alloc_count;
            return (void*) 0;
            }
#else /* HAVE_MMAP */
        /* Read the file into memory. */
        m->addr = (void*) malloc( m->size );
        if ( m->addr == (void*) 0 )
            {
            syslog( LOG_ERR, "out of memory storing a file" );
            (void) close( fd );
            free( (void*) m );
            --alloc_count;
            return (void*) 0;
            }
        if ( read( fd, m->addr, m->size ) != m->size )
            {
            syslog( LOG_ERR, "read - %m" );
            (void) close( fd );
            free( (void*) m );
            --alloc_count;
            return (void*) 0;
            }
#endif /* HAVE_MMAP */
        }
    (void) close( fd );

    /* Put the Map into the hash table. */
    if ( add_hash( m ) < 0 )
        {
        syslog( LOG_ERR, "add_hash() failure" );
        free( (void*) m );
        --alloc_count;
        return (void*) 0;
        }

    /* Put the Map on the active list. */
    m->next = maps;
    maps = m;
    ++map_count;

    /* And return the address. */
    return m->addr;
    }


void
mmc_unmap( void* addr, struct stat* sbP, struct timeval* nowP )
    {
    Map* m = (Map*) 0;

    /* Find the Map entry for this address.  First try a hash. */
    if ( sbP != (struct stat*) 0 )
        {
        m = find_hash( sbP->st_ino, sbP->st_dev, sbP->st_size, sbP->st_ctime );
        if ( m != (Map*) 0 && m->addr != addr )
            m = (Map*) 0;
        }
    /* If that didn't work, try a full search. */
    if ( m == (Map*) 0 )
        for ( m = maps; m != (Map*) 0; m = m->next )
            if ( m->addr == addr )
                break;
    if ( m == (Map*) 0 )
        syslog( LOG_ERR, "mmc_unmap failed to find entry!" );
    else if ( m->refcount <= 0 )
        syslog( LOG_ERR, "mmc_unmap found zero or negative refcount!" );
    else
        {
        --m->refcount;
        if ( nowP != (struct timeval*) 0 )
            m->reftime = nowP->tv_sec;
        else
            m->reftime = time( (time_t*) 0 );
        }
    }


void
mmc_cleanup( struct timeval* nowP )
    {
    time_t now;
    Map** mm;
    Map* m;

    /* Get the current time, if necessary. */
    if ( nowP != (struct timeval*) 0 )
        now = nowP->tv_sec;
    else
        now = time( (time_t*) 0 );

    /* Really unmap any unreferenced entries older than the age limit. */
    for ( mm = &maps; *mm != (Map*) 0; )
        {
        m = *mm;
        if ( m->refcount == 0 && now - m->reftime >= expire_age )
            really_unmap( mm );
        else
            mm = &(*mm)->next;
        }

    /* If there are still too many (or too few) maps, adjust the age limit. */
    if ( map_count > DESIRED_MAX_MAPPED_FILES )
        expire_age = max( ( expire_age * 2 ) / 3, DEFAULT_EXPIRE_AGE / 10 );
    else if ( map_count < DESIRED_MAX_MAPPED_FILES / 2 )
        expire_age = min( ( expire_age * 5 ) / 4, DEFAULT_EXPIRE_AGE * 3 );

    /* Really free excess blocks on the free list. */
    while ( free_count > DESIRED_FREE_COUNT )
        {
        m = free_maps;
        free_maps = m->next;
        --free_count;
        free( (void*) m );
        --alloc_count;
        }
    }


static void
really_unmap( Map** mm )
    {
    Map* m;

    m = *mm;
    if ( m->size != 0 )
        {
#ifdef HAVE_MMAP
        if ( munmap( m->addr, m->size ) < 0 )
            syslog( LOG_ERR, "munmap - %m" );
#else /* HAVE_MMAP */
        free( (void*) m->addr );
#endif /* HAVE_MMAP */
        }
    /* And move the Map to the free list. */
    *mm = m->next;
    --map_count;
    m->next = free_maps;
    free_maps = m;
    ++free_count;
    /* This will sometimes break hash chains, but that's harmless; the
    ** unmapping code that searches the hash table knows to keep searching.
    */
    hash_table[m->hash_idx] = (Map*) 0;
    }


void
mmc_destroy( void )
    {
    Map* m;

    while ( maps != (Map*) 0 )
        really_unmap( &maps );
    while ( free_maps != (Map*) 0 )
        {
        m = free_maps;
        free_maps = m->next;
        --free_count;
        free( (void*) m );
        --alloc_count;
        }
    }


/* Make sure the hash table is big enough. */
static int
check_hash_size( void )
    {
    int i;
    Map* m;

    /* Are we just starting out? */
    if ( hash_table == (Map**) 0 )
        {
        hash_size = INITIAL_HASH_SIZE;
        hash_mask = hash_size - 1;
        }
    /* Is it at least three times bigger than the number of entries? */
    else if ( hash_size >= map_count * 3 )
        return 0;
    else
        {
        /* No, got to expand. */
        free( (void*) hash_table );
        /* Double the hash size until it's big enough. */
        do
            {
            hash_size = hash_size << 1;
            }
        while ( hash_size < map_count * 6 );
        hash_mask = hash_size - 1;
        }
    /* Make the new table. */
    hash_table = (Map**) malloc( hash_size * sizeof(Map*) );
    if ( hash_table == (Map**) 0 )
        return -1;
    /* Clear it. */
    for ( i = 0; i < hash_size; ++i )
        hash_table[i] = (Map*) 0;
    /* And rehash all entries. */
    for ( m = maps; m != (Map*) 0; m = m->next )
        if ( add_hash( m ) < 0 )
            return -1;
    return 0;
    }


static int
add_hash( Map* m )
    {
    unsigned int h, he, i;

    h = hash( m->ino, m->dev, m->size, m->ctime );
    he = ( h + hash_size - 1 ) & hash_mask;
    for ( i = h; ; i = ( i + 1 ) & hash_mask )
        {
        if ( hash_table[i] == (Map*) 0 )
            {
            hash_table[i] = m;
            m->hash = h;
            m->hash_idx = i;
            return 0;
            }
        if ( i == he )
            break;
        }
    return -1;
    }


static Map*
find_hash( ino_t ino, dev_t dev, off_t size, time_t ctime )
    {
    unsigned int h, he, i;
    Map* m;

    h = hash( ino, dev, size, ctime );
    he = ( h + hash_size - 1 ) & hash_mask;
    for ( i = h; ; i = ( i + 1 ) & hash_mask )
        {
        m = hash_table[i];
        if ( m == (Map*) 0 )
            break;
        if ( m->hash == h && m->ino == ino && m->dev == dev &&
             m->size == size && m->ctime == ctime )
            return m;
        if ( i == he )
            break;
        }
    return (Map*) 0;
    }


static unsigned int
hash( ino_t ino, dev_t dev, off_t size, time_t ctime )
    {
    unsigned int h = 177573;

    h ^= ino;
    h += h << 5;
    h ^= dev;
    h += h << 5;
    h ^= size;
    h += h << 5;
    h ^= ctime;

    return h & hash_mask;
    }


/* Generate debugging statistics syslog message. */
void
mmc_logstats( long secs )
    {
    syslog(
        LOG_NOTICE, "  map cache - %d allocated, %d active, %d free; hash size: %d; expire age: %ld",
        alloc_count, map_count, free_count, hash_size, expire_age );
    if ( map_count + free_count != alloc_count )
        syslog( LOG_ERR, "map counts don't add up!" );
    }
Revision:	1.1
Committed:	Mon Jun 18 21:11:57 2001 UTC (25 years, 3 months ago) by root
Content type:	text/plain
Branch:	MAIN
CVS Tags:	mp_j, dp_j, cp_j, HEAD
Branch point for:	connpatch, dirpatch, mmapppatch
Log Message:	* empty log message *
#	Content
1	/* mmc.c - mmap cache
2	**
3	** Copyright © 1998,2001 by Jef Poskanzer <jef@acme.com>.
4	** All rights reserved.
5	**
6	** Redistribution and use in source and binary forms, with or without
7	** modification, are permitted provided that the following conditions
8	** are met:
9	** 1. Redistributions of source code must retain the above copyright
10	** notice, this list of conditions and the following disclaimer.
11	** 2. Redistributions in binary form must reproduce the above copyright
12	** notice, this list of conditions and the following disclaimer in the
13	** documentation and/or other materials provided with the distribution.
14	**
15	** THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16	** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17	** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18	** ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19	** FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20	** DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21	** OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22	** HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23	** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24	** OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25	** SUCH DAMAGE.
26	*/
27
28	#include <sys/types.h>
29	#include <sys/stat.h>
30	#include <sys/time.h>
31	#include <stdlib.h>
32	#include <unistd.h>
33	#include <fcntl.h>
34	#include <syslog.h>
35
36	#ifdef HAVE_MMAP
37	#include <sys/mman.h>
38	#endif /* HAVE_MMAP */
39
40	#include "mmc.h"
41
42
43	/* Defines. */
44	#ifndef DEFAULT_EXPIRE_AGE
45	#define DEFAULT_EXPIRE_AGE 600
46	#endif
47	#ifndef DESIRED_FREE_COUNT
48	#define DESIRED_FREE_COUNT 100
49	#endif
50	#ifndef DESIRED_MAX_MAPPED_FILES
51	#define DESIRED_MAX_MAPPED_FILES 2000
52	#endif
53	#ifndef INITIAL_HASH_SIZE
54	#define INITIAL_HASH_SIZE (1 << 10)
55	#endif
56
57	#define max(a,b) ((a)>(b)?(a):(b))
58	#define min(a,b) ((a)<(b)?(a):(b))
59
60
61	/* The Map struct. */
62	typedef struct MapStruct {
63	ino_t ino;
64	dev_t dev;
65	off_t size;
66	time_t ctime;
67	int refcount;
68	time_t reftime;
69	void* addr;
70	unsigned int hash;
71	int hash_idx;
72	struct MapStruct* next;
73	} Map;
74
75
76	/* Globals. */
77	static Map* maps = (Map*) 0;
78	static Map* free_maps = (Map*) 0;
79	static int alloc_count = 0, map_count = 0, free_count = 0;
80	static Map hash_table = (Map) 0;
81	static int hash_size;
82	static unsigned int hash_mask;
83	static time_t expire_age = DEFAULT_EXPIRE_AGE;
84
85
86
87	/* Forwards. */
88	static void really_unmap( Map** mm );
89	static int check_hash_size( void );
90	static int add_hash( Map* m );
91	static Map* find_hash( ino_t ino, dev_t dev, off_t size, time_t ctime );
92	static unsigned int hash( ino_t ino, dev_t dev, off_t size, time_t ctime );
93
94
95	void*
96	mmc_map( char* filename, struct stat* sbP, struct timeval* nowP )
97	{
98	time_t now;
99	struct stat sb;
100	Map* m;
101	int fd;
102
103	/* Stat the file, if necessary. */
104	if ( sbP != (struct stat*) 0 )
105	sb = *sbP;
106	else
107	{
108	if ( stat( filename, &sb ) != 0 )
109	{
110	syslog( LOG_ERR, "stat - %m" );
111	return (void*) 0;
112	}
113	}
114
115	/* Get the current time, if necessary. */
116	if ( nowP != (struct timeval*) 0 )
117	now = nowP->tv_sec;
118	else
119	now = time( (time_t*) 0 );
120
121	/* See if we have it mapped already, via the hash table. */
122	if ( check_hash_size() < 0 )
123	{
124	syslog( LOG_ERR, "check_hash_size() failure" );
125	return (void*) 0;
126	}
127	m = find_hash( sb.st_ino, sb.st_dev, sb.st_size, sb.st_ctime );
128	if ( m != (Map*) 0 )
129	{
130	/* Yep. Just return the existing map */
131	++m->refcount;
132	m->reftime = now;
133	return m->addr;
134	}
135
136	/* Open the file. */
137	fd = open( filename, O_RDONLY );
138	if ( fd < 0 )
139	{
140	syslog( LOG_ERR, "open - %m" );
141	return (void*) 0;
142	}
143
144	/* Find a free Map entry or make a new one. */
145	if ( free_maps != (Map*) 0 )
146	{
147	m = free_maps;
148	free_maps = m->next;
149	--free_count;
150	}
151	else
152	{
153	m = (Map*) malloc( sizeof(Map) );
154	if ( m == (Map*) 0 )
155	{
156	(void) close( fd );
157	syslog( LOG_ERR, "out of memory allocating a Map" );
158	return (void*) 0;
159	}
160	++alloc_count;
161	}
162
163	/* Fill in the Map entry. */
164	m->ino = sb.st_ino;
165	m->dev = sb.st_dev;
166	m->size = sb.st_size;
167	m->ctime = sb.st_ctime;
168	m->refcount = 1;
169	m->reftime = now;
170
171	/* Avoid doing anything for zero-length files; some systems don't like
172	** to mmap them, other systems dislike mallocing zero bytes.
173	*/
174	if ( m->size == 0 )
175	m->addr = (void) 1; / arbitrary non-NULL address */
176	else
177	{
178	#ifdef HAVE_MMAP
179	/* Map the file into memory. */
180	m->addr = mmap( 0, m->size, PROT_READ, MAP_SHARED, fd, 0 );
181	if ( m->addr == (void*) -1 )
182	{
183	syslog( LOG_ERR, "mmap - %m" );
184	(void) close( fd );
185	free( (void*) m );
186	--alloc_count;
187	return (void*) 0;
188	}
189	#else /* HAVE_MMAP */
190	/* Read the file into memory. */
191	m->addr = (void*) malloc( m->size );
192	if ( m->addr == (void*) 0 )
193	{
194	syslog( LOG_ERR, "out of memory storing a file" );
195	(void) close( fd );
196	free( (void*) m );
197	--alloc_count;
198	return (void*) 0;
199	}
200	if ( read( fd, m->addr, m->size ) != m->size )
201	{
202	syslog( LOG_ERR, "read - %m" );
203	(void) close( fd );
204	free( (void*) m );
205	--alloc_count;
206	return (void*) 0;
207	}
208	#endif /* HAVE_MMAP */
209	}
210	(void) close( fd );
211
212	/* Put the Map into the hash table. */
213	if ( add_hash( m ) < 0 )
214	{
215	syslog( LOG_ERR, "add_hash() failure" );
216	free( (void*) m );
217	--alloc_count;
218	return (void*) 0;
219	}
220
221	/* Put the Map on the active list. */
222	m->next = maps;
223	maps = m;
224	++map_count;
225
226	/* And return the address. */
227	return m->addr;
228	}
229
230
231	void
232	mmc_unmap( void* addr, struct stat* sbP, struct timeval* nowP )
233	{
234	Map* m = (Map*) 0;
235
236	/* Find the Map entry for this address. First try a hash. */
237	if ( sbP != (struct stat*) 0 )
238	{
239	m = find_hash( sbP->st_ino, sbP->st_dev, sbP->st_size, sbP->st_ctime );
240	if ( m != (Map*) 0 && m->addr != addr )
241	m = (Map*) 0;
242	}
243	/* If that didn't work, try a full search. */
244	if ( m == (Map*) 0 )
245	for ( m = maps; m != (Map*) 0; m = m->next )
246	if ( m->addr == addr )
247	break;
248	if ( m == (Map*) 0 )
249	syslog( LOG_ERR, "mmc_unmap failed to find entry!" );
250	else if ( m->refcount <= 0 )
251	syslog( LOG_ERR, "mmc_unmap found zero or negative refcount!" );
252	else
253	{
254	--m->refcount;
255	if ( nowP != (struct timeval*) 0 )
256	m->reftime = nowP->tv_sec;
257	else
258	m->reftime = time( (time_t*) 0 );
259	}
260	}
261
262
263	void
264	mmc_cleanup( struct timeval* nowP )
265	{
266	time_t now;
267	Map** mm;
268	Map* m;
269
270	/* Get the current time, if necessary. */
271	if ( nowP != (struct timeval*) 0 )
272	now = nowP->tv_sec;
273	else
274	now = time( (time_t*) 0 );
275
276	/* Really unmap any unreferenced entries older than the age limit. */
277	for ( mm = &maps; mm != (Map) 0; )
278	{
279	m = *mm;
280	if ( m->refcount == 0 && now - m->reftime >= expire_age )
281	really_unmap( mm );
282	else
283	mm = &(*mm)->next;
284	}
285
286	/* If there are still too many (or too few) maps, adjust the age limit. */
287	if ( map_count > DESIRED_MAX_MAPPED_FILES )
288	expire_age = max( ( expire_age * 2 ) / 3, DEFAULT_EXPIRE_AGE / 10 );
289	else if ( map_count < DESIRED_MAX_MAPPED_FILES / 2 )
290	expire_age = min( ( expire_age * 5 ) / 4, DEFAULT_EXPIRE_AGE * 3 );
291
292	/* Really free excess blocks on the free list. */
293	while ( free_count > DESIRED_FREE_COUNT )
294	{
295	m = free_maps;
296	free_maps = m->next;
297	--free_count;
298	free( (void*) m );
299	--alloc_count;
300	}
301	}
302
303
304	static void
305	really_unmap( Map** mm )
306	{
307	Map* m;
308
309	m = *mm;
310	if ( m->size != 0 )
311	{
312	#ifdef HAVE_MMAP
313	if ( munmap( m->addr, m->size ) < 0 )
314	syslog( LOG_ERR, "munmap - %m" );
315	#else /* HAVE_MMAP */
316	free( (void*) m->addr );
317	#endif /* HAVE_MMAP */
318	}
319	/* And move the Map to the free list. */
320	*mm = m->next;
321	--map_count;
322	m->next = free_maps;
323	free_maps = m;
324	++free_count;
325	/* This will sometimes break hash chains, but that's harmless; the
326	** unmapping code that searches the hash table knows to keep searching.
327	*/
328	hash_table[m->hash_idx] = (Map*) 0;
329	}
330
331
332	void
333	mmc_destroy( void )
334	{
335	Map* m;
336
337	while ( maps != (Map*) 0 )
338	really_unmap( &maps );
339	while ( free_maps != (Map*) 0 )
340	{
341	m = free_maps;
342	free_maps = m->next;
343	--free_count;
344	free( (void*) m );
345	--alloc_count;
346	}
347	}
348
349
350	/* Make sure the hash table is big enough. */
351	static int
352	check_hash_size( void )
353	{
354	int i;
355	Map* m;
356
357	/* Are we just starting out? */
358	if ( hash_table == (Map**) 0 )
359	{
360	hash_size = INITIAL_HASH_SIZE;
361	hash_mask = hash_size - 1;
362	}
363	/* Is it at least three times bigger than the number of entries? */
364	else if ( hash_size >= map_count * 3 )
365	return 0;
366	else
367	{
368	/* No, got to expand. */
369	free( (void*) hash_table );
370	/* Double the hash size until it's big enough. */
371	do
372	{
373	hash_size = hash_size << 1;
374	}
375	while ( hash_size < map_count * 6 );
376	hash_mask = hash_size - 1;
377	}
378	/* Make the new table. */
379	hash_table = (Map*) malloc( hash_size sizeof(Map*) );
380	if ( hash_table == (Map**) 0 )
381	return -1;
382	/* Clear it. */
383	for ( i = 0; i < hash_size; ++i )
384	hash_table[i] = (Map*) 0;
385	/* And rehash all entries. */
386	for ( m = maps; m != (Map*) 0; m = m->next )
387	if ( add_hash( m ) < 0 )
388	return -1;
389	return 0;
390	}
391
392
393	static int
394	add_hash( Map* m )
395	{
396	unsigned int h, he, i;
397
398	h = hash( m->ino, m->dev, m->size, m->ctime );
399	he = ( h + hash_size - 1 ) & hash_mask;
400	for ( i = h; ; i = ( i + 1 ) & hash_mask )
401	{
402	if ( hash_table[i] == (Map*) 0 )
403	{
404	hash_table[i] = m;
405	m->hash = h;
406	m->hash_idx = i;
407	return 0;
408	}
409	if ( i == he )
410	break;
411	}
412	return -1;
413	}
414
415
416	static Map*
417	find_hash( ino_t ino, dev_t dev, off_t size, time_t ctime )
418	{
419	unsigned int h, he, i;
420	Map* m;
421
422	h = hash( ino, dev, size, ctime );
423	he = ( h + hash_size - 1 ) & hash_mask;
424	for ( i = h; ; i = ( i + 1 ) & hash_mask )
425	{
426	m = hash_table[i];
427	if ( m == (Map*) 0 )
428	break;
429	if ( m->hash == h && m->ino == ino && m->dev == dev &&
430	m->size == size && m->ctime == ctime )
431	return m;
432	if ( i == he )
433	break;
434	}
435	return (Map*) 0;
436	}
437
438
439	static unsigned int
440	hash( ino_t ino, dev_t dev, off_t size, time_t ctime )
441	{
442	unsigned int h = 177573;
443
444	h ^= ino;
445	h += h << 5;
446	h ^= dev;
447	h += h << 5;
448	h ^= size;
449	h += h << 5;
450	h ^= ctime;
451
452	return h & hash_mask;
453	}
454
455
456	/* Generate debugging statistics syslog message. */
457	void
458	mmc_logstats( long secs )
459	{
460	syslog(
461	LOG_NOTICE, " map cache - %d allocated, %d active, %d free; hash size: %d; expire age: %ld",
462	alloc_count, map_count, free_count, hash_size, expire_age );
463	if ( map_count + free_count != alloc_count )
464	syslog( LOG_ERR, "map counts don't add up!" );
465	}