summaryrefslogtreecommitdiffstats
path: root/bftw.c
blob: 9b990e724c5c2dd3d35632add857ff9fda403778 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
/*********************************************************************
 * bfs                                                               *
 * Copyright (C) 2015 Tavian Barnes <tavianator@tavianator.com>      *
 *                                                                   *
 * This program is free software. It comes without any warranty, to  *
 * the extent permitted by applicable law. You can redistribute it   *
 * and/or modify it under the terms of the Do What The Fuck You Want *
 * To Public License, Version 2, as published by Sam Hocevar. See    *
 * the COPYING file or http://www.wtfpl.net/ for more details.       *
 *********************************************************************/

/**
 * bftw() implementation.
 *
 * The goal of this implementation is to avoid re-traversal by using openat() as
 * much as possible.  The 'dircache' attempts to accomplish this by storing a
 * hierarchy of 'dircache_entry's, along with an LRU list of recently accessed
 * entries.  Every entry in the LRU list has an open DIR *; to open an entry, we
 * traverse its chain of parents, hoping to find an open one.  The size of the
 * LRU list is limited, because so are the available file descriptors.
 *
 * The 'dirqueue' is a simple FIFO of 'dircache_entry's left to explore.
 */

#include "bftw.h"
#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

/**
 * Simple dynamically-sized string type.
 */
typedef struct {
	char *str;
	size_t length;
	size_t capacity;
} dynstr;

/** Initialize a dynstr. */
static void dynstr_init(dynstr *dstr) {
	dstr->str = NULL;
	dstr->length = 0;
	dstr->capacity = 0;
}

/** Grow a dynstr to the given capacity if necessary. */
static int dynstr_grow(dynstr *dstr, size_t length) {
	if (length >= dstr->capacity) {
		size_t new_capacity = 3*(length + 1)/2;
		char *new_str = realloc(dstr->str, new_capacity);
		if (!new_str) {
			return -1;
		}

		dstr->str = new_str;
		dstr->capacity = new_capacity;
	}

	return 0;
}

/** Concatenate a string to a dynstr at the given position. */
static int dynstr_concat(dynstr *dstr, size_t pos, const char *more) {
	size_t morelen = strlen(more);
	size_t length = pos + morelen;
	if (dynstr_grow(dstr, length) != 0) {
		return -1;
	}

	memcpy(dstr->str + pos, more, morelen + 1);
	dstr->length = length;
	return 0;
}

/** Free a dynstr. */
static void dynstr_free(dynstr *dstr) {
	free(dstr->str);
}

/**
 * A single entry in the dircache.
 */
typedef struct dircache_entry dircache_entry;

struct dircache_entry {
	/** The parent entry, if any. */
	dircache_entry *parent;
	/** This directory's depth in the walk. */
	size_t depth;

	/** Previous node in the LRU list. */
	dircache_entry *lru_prev;
	/** Next node in the LRU list. */
	dircache_entry *lru_next;

	/** The DIR pointer, if open. */
	DIR *dir;

	/** Reference count. */
	size_t refcount;

	/** The length of the directory's name. */
	size_t namelen;
	/** The directory's name. */
	char name[];
};

/**
 * A directory cache.
 */
typedef struct {
	/** Most recently used entry. */
	dircache_entry *lru_head;
	/** Least recently used entry. */
	dircache_entry *lru_tail;
	/** Remaining LRU list capacity. */
	size_t lru_remaining;
} dircache;

/** Initialize a dircache. */
static void dircache_init(dircache *cache, size_t lru_size) {
	assert(lru_size > 0);
	cache->lru_head = cache->lru_tail = NULL;
	cache->lru_remaining = lru_size;
}

/** Add an entry to the dircache. */
static dircache_entry *dircache_add(dircache *cache, dircache_entry *parent, const char *path) {
	size_t pathsize = strlen(path) + 1;
	dircache_entry *entry = malloc(sizeof(dircache_entry) + pathsize);
	if (entry) {
		entry->parent = parent;
		entry->depth = parent ? parent->depth + 1 : 0;
		entry->lru_prev = entry->lru_next = NULL;
		entry->dir = NULL;
		entry->refcount = 1;
		entry->namelen = pathsize - 1;
		memcpy(entry->name, path, pathsize);

		while (parent) {
			++parent->refcount;
			parent = parent->parent;
		}
	}
	return entry;
}

/** Add an entry to the head of the LRU list. */
static void dircache_lru_add(dircache *cache, dircache_entry *entry) {
	assert(entry->dir);
	assert(entry->lru_prev == NULL);
	assert(entry->lru_next == NULL);

	entry->lru_next = cache->lru_head;
	cache->lru_head = entry;

	if (entry->lru_next) {
		entry->lru_next->lru_prev = entry;
	}

	if (!cache->lru_tail) {
		cache->lru_tail = entry;
	}

	--cache->lru_remaining;
}

/** Remove an entry from the LRU list. */
static void dircache_lru_remove(dircache *cache, dircache_entry *entry) {
	if (entry->lru_prev) {
		assert(cache->lru_head != entry);
		entry->lru_prev->lru_next = entry->lru_next;
	} else {
		assert(cache->lru_head == entry);
		cache->lru_head = entry->lru_next;
	}

	if (entry->lru_next) {
		assert(cache->lru_tail != entry);
		entry->lru_next->lru_prev = entry->lru_prev;
	} else {
		assert(cache->lru_tail == entry);
		cache->lru_tail = entry->lru_prev;
	}

	entry->lru_prev = entry->lru_next = NULL;

	++cache->lru_remaining;
}

/** Close a dircache_entry and remove it from the LRU list. */
static void dircache_entry_close(dircache *cache, dircache_entry *entry) {
	dircache_lru_remove(cache, entry);
	closedir(entry->dir);
	entry->dir = NULL;
}

/** POSIX doesn't have this?! */
static DIR *opendirat(int fd, const char *name) {
	int dfd = openat(fd, name, O_DIRECTORY);
	if (dfd < 0) {
		return NULL;
	}

	return fdopendir(dfd);
}

/**
 * Open a dircache_entry.
 *
 * @param cache
 *         The cache containing the entry.
 * @param entry
 *         The entry to open.
 * @param[out] path
 *         Will hold the full path to the entry, with a trailing '/'.
 * @return
 *         The opened DIR *, or NULL on error.
 */
static DIR *dircache_entry_open(dircache *cache, dircache_entry *entry, dynstr *path) {
	assert(!entry->dir);

	if (cache->lru_remaining == 0) {
		dircache_entry_close(cache, cache->lru_tail);
	}

	// First, reserve enough space for the path
	size_t pathlen = 0;

	dircache_entry *parent = entry;
	do {
		size_t namelen = parent->namelen;
		pathlen += namelen;

		if (namelen > 0 && parent->name[namelen - 1] != '/') {
			++pathlen;
		}

		parent = parent->parent;
	} while (parent);

	if (dynstr_grow(path, pathlen) != 0) {
		return NULL;
	}
	path->length = pathlen;

	// Now, build the path backwards while looking for a parent
	char *segment = path->str + pathlen;
	*segment = '\0';

	int fd = AT_FDCWD;
	const char *relpath = path->str;

	parent = entry;
	while (true) {
		size_t namelen = parent->namelen;
		bool needs_slash = namelen > 0 && parent->name[namelen - 1] != '/';

		segment -= namelen;
		if (needs_slash) {
			segment -= 1;
		}

		memcpy(segment, parent->name, namelen);

		if (needs_slash) {
			segment[namelen] = '/';
		}

		parent = parent->parent;
		if (!parent) {
			break;
		}

		if (parent->dir && fd == AT_FDCWD) {
			dircache_lru_remove(cache, parent);
			dircache_lru_add(cache, parent);
			fd = dirfd(parent->dir);
			relpath = segment;
		}
	}

	DIR *dir = opendirat(fd, relpath);
	if (dir) {
		entry->dir = dir;
		dircache_lru_add(cache, entry);
	}

	return dir;
}

/** Free a dircache_entry. */
static void dircache_entry_free(dircache *cache, dircache_entry *entry) {
	while (entry) {
		dircache_entry *saved = entry;
		entry = entry->parent;

		if (--saved->refcount == 0) {
			if (saved->dir) {
				dircache_entry_close(cache, saved);
			}
			free(saved);
		}
	}
}

/** The size of a dirqueue block. */
#define DIRQUEUE_BLOCK_SIZE 1023

/**
 * A single block in the dirqueue chain.
 */
typedef struct dirqueue_block dirqueue_block;

struct dirqueue_block {
	/** The next block in the chain. */
	dirqueue_block *next;
	/** The elements in the queue. */
	dircache_entry *entries[DIRQUEUE_BLOCK_SIZE];
};

/**
 * A queue of 'dircache_entry's to examine.
 */
typedef struct {
	/** The first block. */
	dirqueue_block *head;
	/** The last block. */
	dirqueue_block *tail;
	/** The index in 'head' of the next entry to read. */
	size_t front;
	/** The index in 'tail' of the next entry to write. */
	size_t back;
} dirqueue;

/** Initialize a dirqueue. */
static void dirqueue_init(dirqueue *queue) {
	queue->head = queue->tail = NULL;
	queue->front = 0;
	queue->back = DIRQUEUE_BLOCK_SIZE;
}

/** Add an entry to the dirqueue. */
static int dirqueue_push(dirqueue *queue, dircache_entry *entry) {
	if (queue->back == DIRQUEUE_BLOCK_SIZE) {
		dirqueue_block *block = malloc(sizeof(dirqueue_block));
		if (!block) {
			return -1;
		}

		block->next = NULL;

		if (queue->tail) {
			queue->tail->next = block;
		}
		queue->tail = block;

		if (!queue->head) {
			queue->head = block;
		}

		queue->back = 0;
	}

	queue->tail->entries[queue->back++] = entry;
	return 0;
}

/** Remove an entry from the dirqueue. */
static dircache_entry *dirqueue_pop(dirqueue *queue) {
	if (!queue->head) {
		return NULL;
	}

	if (queue->head == queue->tail && queue->front == queue->back) {
		free(queue->head);
		dirqueue_init(queue);
		return NULL;
	}

	dirqueue_block *head = queue->head;
	dircache_entry *entry = head->entries[queue->front];
	if (++queue->front == DIRQUEUE_BLOCK_SIZE) {
		queue->head = head->next;
		queue->front = 0;
		free(head);
	}
	return entry;
}

int bftw(const char *dirpath, bftw_fn *fn, int nopenfd, int flags, void *ptr) {
	int ret = -1, err;

	dircache cache;
	dircache_init(&cache, nopenfd);

	dirqueue queue;
	dirqueue_init(&queue);

	dynstr path;
	dynstr_init(&path);

	dircache_entry *current = dircache_add(&cache, NULL, dirpath);
	if (!current) {
		goto done;
	}

	do {
		DIR *dir = dircache_entry_open(&cache, current, &path);
		if (!dir) {
			goto done;
		}

		size_t pathlen = path.length;

		struct dirent *de;
		while ((de = readdir(dir)) != NULL) {
			if (strcmp(de->d_name, ".") == 0 || strcmp(de->d_name, "..") == 0) {
				continue;
			}

			struct BFTW ftwbuf = {
				.statbuf = NULL,
				.typeflag = BFTW_UNKNOWN,
				.base = pathlen,
				.level = current->depth + 1,
			};

			if (dynstr_concat(&path, pathlen, de->d_name) != 0) {
				goto done;
			}

#if defined(_DIRENT_HAVE_D_TYPE) || defined(DT_DIR)
			switch (de->d_type) {
			case DT_DIR:
				ftwbuf.typeflag = BFTW_D;
				break;
			case DT_REG:
				ftwbuf.typeflag = BFTW_R;
				break;
			case DT_LNK:
				ftwbuf.typeflag = BFTW_SL;
				break;
			}
#endif

			struct stat sb;

			if ((flags & BFTW_STAT) || ftwbuf.typeflag == BFTW_UNKNOWN) {
				if (fstatat(dirfd(dir), de->d_name, &sb, AT_SYMLINK_NOFOLLOW) == 0) {
					ftwbuf.statbuf = &sb;

					switch (sb.st_mode & S_IFMT) {
					case S_IFDIR:
						ftwbuf.typeflag = BFTW_D;
						break;
					case S_IFREG:
						ftwbuf.typeflag = BFTW_R;
						break;
					case S_IFLNK:
						ftwbuf.typeflag = BFTW_SL;
						break;
					}
				}
			}

			int action = fn(path.str, &ftwbuf, ptr);

			switch (action) {
			case BFTW_CONTINUE:
				if (ftwbuf.typeflag == BFTW_D) {
					dircache_entry *next = dircache_add(&cache, current, de->d_name);
					if (!next) {
						goto done;
					}

					if (dirqueue_push(&queue, next) != 0) {
						goto done;
					}
				}
				break;

			case BFTW_SKIP_SIBLINGS:
				goto next;

			case BFTW_SKIP_SUBTREE:
				break;

			case BFTW_STOP:
				ret = 0;
				goto done;

			default:
				errno = EINVAL;
				goto done;
			}
		}

	next:
		dircache_entry_free(&cache, current);
		current = dirqueue_pop(&queue);
	} while (current);

	ret = 0;
done:
	err = errno;

	while (current) {
		dircache_entry_free(&cache, current);
		current = dirqueue_pop(&queue);
	}

	dynstr_free(&path);

	errno = err;
	return ret;
}