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2876 jermar 1
/*
2
 * Copyright (c) 2008 Jakub Jermar
3
 * All rights reserved.
4
 *
5
 * Redistribution and use in source and binary forms, with or without
6
 * modification, are permitted provided that the following conditions
7
 * are met:
8
 *
9
 * - Redistributions of source code must retain the above copyright
10
 *   notice, this list of conditions and the following disclaimer.
11
 * - 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
 * - The name of the author may not be used to endorse or promote products
15
 *   derived from this software without specific prior written permission.
16
 *
17
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
 */
28
 
29
/** @addtogroup fs
30
 * @{
31
 */
32
 
33
/**
34
 * @file    fat_idx.c
35
 * @brief   Layer for translating FAT entities to VFS node indices.
36
 */
37
 
38
#include "fat.h"
2881 jermar 39
#include "../../vfs/vfs.h"
2876 jermar 40
#include <errno.h>
41
#include <string.h>
42
#include <libadt/hash_table.h>
43
#include <libadt/list.h>
44
#include <assert.h>
45
#include <futex.h>
46
 
2881 jermar 47
/** Each instance of this type describes one interval of freed VFS indices. */
48
typedef struct {
49
    link_t      link;
50
    fs_index_t  first;
51
    fs_index_t  last;
52
} freed_t;
53
 
54
/**
55
 * Each instance of this type describes state of all VFS indices that
56
 * are currently unused.
57
 */
58
typedef struct {
59
    link_t      link;
60
    dev_handle_t    dev_handle;
61
 
62
    /** Next unassigned index. */
63
    fs_index_t  next;
64
    /** Number of remaining unassigned indices. */
65
    uint64_t    remaining;
66
 
67
    /** Sorted list of intervals of freed indices. */
68
    link_t      freed_head;
69
} unused_t;
70
 
2948 svoboda 71
/** Futex protecting the list of unused structures. */
72
static futex_t unused_futex = FUTEX_INITIALIZER;
73
 
74
/** List of unused structures. */
2881 jermar 75
static LIST_INITIALIZE(unused_head);
76
 
2948 svoboda 77
/** Futex protecting the up_hash and ui_hash.
78
 *
79
 * The locking strategy assumes that there will be at most one fibril for each
80
 * dev_handle.  Therefore it will be sufficient to hold the futex for shorter
81
 * times (i.e. only during hash table operations as opposed to holding it the
82
 * whole time between an unsuccessful find and the following insert). Should the
83
 * assumption break, the locking strategy for this futex will have to be
84
 * reconsidered.
85
 */
86
static futex_t used_futex = FUTEX_INITIALIZER;
87
 
2890 jermar 88
/**
89
 * Global hash table of all used fat_idx_t structures.
90
 * The index structures are hashed by the dev_handle, parent node's first
91
 * cluster and index within the parent directory.
92
 */
93
static hash_table_t up_hash;
2889 jermar 94
 
2890 jermar 95
#define UPH_BUCKETS_LOG 12
96
#define UPH_BUCKETS (1 << UPH_BUCKETS_LOG)
2889 jermar 97
 
2890 jermar 98
#define UPH_DH_KEY  0
99
#define UPH_PFC_KEY 1
100
#define UPH_PDI_KEY 2
2889 jermar 101
 
2890 jermar 102
static hash_index_t pos_hash(unsigned long key[])
2889 jermar 103
{
2890 jermar 104
    dev_handle_t dev_handle = (dev_handle_t)key[UPH_DH_KEY];
105
    fat_cluster_t pfc = (fat_cluster_t)key[UPH_PFC_KEY];
106
    unsigned pdi = (unsigned)key[UPH_PDI_KEY];
2889 jermar 107
 
108
    hash_index_t h;
109
 
110
    /*
111
     * The least significant half of all bits are the least significant bits
112
     * of the parent node's first cluster.
113
     *
114
     * The least significant half of the most significant half of all bits
115
     * are the least significant bits of the node's dentry index within the
116
     * parent directory node.
117
     *
118
     * The most significant half of the most significant half of all bits
119
     * are the least significant bits of the device handle.
120
     */
2890 jermar 121
    h = pfc & ((1 << (UPH_BUCKETS_LOG / 2)) - 1);
122
    h |= (pdi & ((1 << (UPH_BUCKETS_LOG / 4)) - 1)) <<
123
        (UPH_BUCKETS_LOG / 2);
124
    h |= (dev_handle & ((1 << (UPH_BUCKETS_LOG / 4)) - 1)) <<
125
        (3 * (UPH_BUCKETS_LOG / 4));
2889 jermar 126
 
127
    return h;
128
}
129
 
2890 jermar 130
static int pos_compare(unsigned long key[], hash_count_t keys, link_t *item)
2889 jermar 131
{
2890 jermar 132
    dev_handle_t dev_handle = (dev_handle_t)key[UPH_DH_KEY];
133
    fat_cluster_t pfc = (fat_cluster_t)key[UPH_PFC_KEY];
134
    unsigned pdi = (unsigned)key[UPH_PDI_KEY];
135
    fat_idx_t *fidx = list_get_instance(item, fat_idx_t, uph_link);
2889 jermar 136
 
137
    return (dev_handle == fidx->dev_handle) && (pfc == fidx->pfc) &&
138
        (pdi == fidx->pdi);
139
}
140
 
2890 jermar 141
static void pos_remove_callback(link_t *item)
142
{
143
    /* nothing to do */
144
}
145
 
146
static hash_table_operations_t uph_ops = {
147
    .hash = pos_hash,
148
    .compare = pos_compare,
149
    .remove_callback = pos_remove_callback,
150
};
151
 
152
/**
153
 * Global hash table of all used fat_idx_t structures.
154
 * The index structures are hashed by the dev_handle and index.
155
 */
156
static hash_table_t ui_hash;
157
 
158
#define UIH_BUCKETS_LOG 12
159
#define UIH_BUCKETS (1 << UIH_BUCKETS_LOG)
160
 
161
#define UIH_DH_KEY  0
162
#define UIH_INDEX_KEY   1
163
 
164
static hash_index_t idx_hash(unsigned long key[])
165
{
166
    dev_handle_t dev_handle = (dev_handle_t)key[UIH_DH_KEY];
167
    fs_index_t index = (fs_index_t)key[UIH_INDEX_KEY];
168
 
169
    hash_index_t h;
170
 
171
    h = dev_handle & ((1 << (UIH_BUCKETS_LOG / 2)) - 1);
172
    h |= (index & ((1 << (UIH_BUCKETS_LOG / 2)) - 1)) <<
173
        (UIH_BUCKETS_LOG / 2);
174
 
175
    return h;
176
}
177
 
178
static int idx_compare(unsigned long key[], hash_count_t keys, link_t *item)
179
{
180
    dev_handle_t dev_handle = (dev_handle_t)key[UIH_DH_KEY];
181
    fs_index_t index = (fs_index_t)key[UIH_INDEX_KEY];
182
    fat_idx_t *fidx = list_get_instance(item, fat_idx_t, uih_link);
183
 
184
    return (dev_handle == fidx->dev_handle) && (index == fidx->index);
185
}
186
 
2889 jermar 187
static void idx_remove_callback(link_t *item)
188
{
189
    /* nothing to do */
190
}
191
 
2890 jermar 192
static hash_table_operations_t uih_ops = {
2889 jermar 193
    .hash = idx_hash,
194
    .compare = idx_compare,
195
    .remove_callback = idx_remove_callback,
196
};
197
 
2881 jermar 198
/** Allocate a VFS index which is not currently in use. */
199
static bool fat_idx_alloc(dev_handle_t dev_handle, fs_index_t *index)
2876 jermar 200
{
2881 jermar 201
    link_t *l;
202
    unused_t *u;
203
 
204
    assert(index);
2948 svoboda 205
    futex_down(&unused_futex);
2881 jermar 206
    for (l = unused_head.next; l != &unused_head; l = l->next) {
207
        u = list_get_instance(l, unused_t, link);
208
        if (u->dev_handle == dev_handle)
209
            goto hit;
210
    }
2948 svoboda 211
    futex_up(&unused_futex);
212
 
2881 jermar 213
    /* dev_handle not found */
214
    return false;  
215
 
216
hit:
217
    if (list_empty(&u->freed_head)) {
218
        if (u->remaining) {
219
            /*
220
             * There are no freed indices, allocate one directly
221
             * from the counter.
222
             */
223
            *index = u->next++;
224
            --u->remaining;
2948 svoboda 225
            futex_up(&unused_futex);
2881 jermar 226
            return true;
227
        }
228
    } else {
229
        /* There are some freed indices which we can reuse. */
230
        freed_t *f = list_get_instance(u->freed_head.next, freed_t,
231
            link);
232
        *index = f->first;
233
        if (f->first++ == f->last) {
234
            /* Destroy the interval. */
235
            list_remove(&f->link);
236
            free(f);
237
        }
2948 svoboda 238
        futex_up(&unused_futex);
2881 jermar 239
        return true;
240
    }
241
    /*
242
     * We ran out of indices, which is extremely unlikely with FAT16, but
243
     * theoretically still possible (e.g. too many open unlinked nodes or
244
     * too many zero-sized nodes).
245
     */
2948 svoboda 246
    futex_up(&unused_futex);
2881 jermar 247
    return false;
248
}
249
 
2884 jermar 250
/** If possible, coalesce two intervals of freed indices. */
251
static void try_coalesce_intervals(link_t *l, link_t *r, link_t *cur)
2881 jermar 252
{
253
    freed_t *fl = list_get_instance(l, freed_t, link);
254
    freed_t *fr = list_get_instance(r, freed_t, link);
255
 
256
    if (fl->last + 1 == fr->first) {
257
        if (cur == l) {
258
            fl->last = fr->last;
259
            list_remove(r);
260
            free(r);
261
        } else {
262
            fr->first = fl->first;
263
            list_remove(l);
264
            free(l);
265
        }
266
    }
267
}
268
 
269
/** Free a VFS index, which is no longer in use. */
270
static void fat_idx_free(dev_handle_t dev_handle, fs_index_t index)
271
{
272
    link_t *l;
273
    unused_t *u;
274
 
2948 svoboda 275
    futex_down(&unused_futex);
2881 jermar 276
    for (l = unused_head.next; l != &unused_head; l = l->next) {
277
        u = list_get_instance(l, unused_t, link);
278
        if (u->dev_handle == dev_handle)
279
            goto hit;
280
    }
2948 svoboda 281
    futex_up(&unused_futex);
2881 jermar 282
 
283
    /* should not happen */
284
    assert(0);
285
 
286
hit:
287
    if (u->next == index + 1) {
288
        /* The index can be returned directly to the counter. */
289
        u->next--;
290
        u->remaining++;
291
    } else {
292
        /*
293
         * The index must be returned either to an existing freed
294
         * interval or a new interval must be created.
295
         */
296
        link_t *lnk;
297
        freed_t *n;
298
        for (lnk = u->freed_head.next; lnk != &u->freed_head;
299
            lnk = lnk->next) {
300
            freed_t *f = list_get_instance(lnk, freed_t, link);
301
            if (f->first == index + 1) {
302
                f->first--;
303
                if (lnk->prev != &u->freed_head)
2884 jermar 304
                    try_coalesce_intervals(lnk->prev, lnk,
2881 jermar 305
                        lnk);
2948 svoboda 306
                futex_up(&unused_futex);
2881 jermar 307
                return;
308
            }
309
            if (f->last == index - 1) {
310
                f->last++;
311
                if (lnk->next != &u->freed_head)
2884 jermar 312
                    try_coalesce_intervals(lnk, lnk->next,
2881 jermar 313
                        lnk);
2948 svoboda 314
                futex_up(&unused_futex);
2881 jermar 315
                return;
316
            }
317
            if (index > f->first) {
318
                n = malloc(sizeof(freed_t));
319
                /* TODO: sleep until allocation succeeds */
320
                assert(n);
321
                link_initialize(&n->link);
322
                n->first = index;
323
                n->last = index;
324
                list_insert_before(&n->link, lnk);
2948 svoboda 325
                futex_up(&unused_futex);
2881 jermar 326
                return;
327
            }
328
 
329
        }
330
        /* The index will form the last interval. */
331
        n = malloc(sizeof(freed_t));
332
        /* TODO: sleep until allocation succeeds */
333
        assert(n);
334
        link_initialize(&n->link);
335
        n->first = index;
336
        n->last = index;
337
        list_append(&n->link, &u->freed_head);
338
    }
2948 svoboda 339
    futex_up(&unused_futex);
2881 jermar 340
}
341
 
2890 jermar 342
fat_idx_t *
343
fat_idx_get_by_pos(dev_handle_t dev_handle, fat_cluster_t pfc, unsigned pdi)
2881 jermar 344
{
2889 jermar 345
    fat_idx_t *fidx;
346
    link_t *l;
2890 jermar 347
    unsigned long pkey[] = {
348
        [UPH_DH_KEY] = dev_handle,
349
        [UPH_PFC_KEY] = pfc,
350
        [UPH_PDI_KEY] = pdi,
2889 jermar 351
    };
352
 
2948 svoboda 353
    futex_down(&used_futex);
2890 jermar 354
    l = hash_table_find(&up_hash, pkey);
2948 svoboda 355
    futex_up(&used_futex);
2889 jermar 356
    if (l) {
2890 jermar 357
        fidx = hash_table_get_instance(l, fat_idx_t, uph_link);
2889 jermar 358
    } else {
359
        fidx = (fat_idx_t *) malloc(sizeof(fat_idx_t));
360
        if (!fidx) {
361
            return NULL;
362
        }
363
        if (!fat_idx_alloc(dev_handle, &fidx->index)) {
364
            free(fidx);
365
            return NULL;
366
        }
2890 jermar 367
 
368
        unsigned long ikey[] = {
369
            [UIH_DH_KEY] = dev_handle,
370
            [UIH_INDEX_KEY] = fidx->index,
371
        };
372
 
373
        link_initialize(&fidx->uph_link);
374
        link_initialize(&fidx->uih_link);
2889 jermar 375
        fidx->dev_handle = dev_handle;
376
        fidx->pfc = pfc;
377
        fidx->pdi = pdi;
378
        fidx->nodep = NULL;
2890 jermar 379
 
2948 svoboda 380
        futex_down(&used_futex);
2890 jermar 381
        hash_table_insert(&up_hash, pkey, &fidx->uph_link);
382
        hash_table_insert(&ui_hash, ikey, &fidx->uih_link);
2948 svoboda 383
        futex_up(&used_futex);
2889 jermar 384
    }
385
 
386
    return fidx;
2876 jermar 387
}
2889 jermar 388
 
2890 jermar 389
fat_idx_t *
390
fat_idx_get_by_index(dev_handle_t dev_handle, fs_index_t index)
391
{
392
    fat_idx_t *fidx = NULL;
393
    link_t *l;
394
    unsigned long ikey[] = {
395
        [UIH_DH_KEY] = dev_handle,
396
        [UIH_INDEX_KEY] = index,
397
    };
398
 
2948 svoboda 399
    futex_down(&used_futex);
2890 jermar 400
    l = hash_table_find(&ui_hash, ikey);
2948 svoboda 401
    futex_up(&used_futex);
2890 jermar 402
    if (l) {
403
        fidx = hash_table_get_instance(l, fat_idx_t, uih_link);
404
    }
405
 
406
    return fidx;
407
}
408