fncache.c

 1// SPDX-License-Identifier: GPL-2.0-only
 2/* Manage a cache of file names' existence */
 3#include <pthread.h>
 4#include <stdlib.h>
 5#include <string.h>
 6#include <unistd.h>
 7#include <linux/compiler.h>
 8#include "fncache.h"
 9#include "hashmap.h"
10
11static struct hashmap *fncache;
12
13static size_t fncache__hash(long key, void *ctx __maybe_unused)
14{
15	return str_hash((const char *)key);
16}
17
18static bool fncache__equal(long key1, long key2, void *ctx __maybe_unused)
19{
20	return strcmp((const char *)key1, (const char *)key2) == 0;
21}
22
23static void fncache__init(void)
24{
25	fncache = hashmap__new(fncache__hash, fncache__equal, /*ctx=*/NULL);
26}
27
28static struct hashmap *fncache__get(void)
29{
30	static pthread_once_t fncache_once = PTHREAD_ONCE_INIT;
31
32	pthread_once(&fncache_once, fncache__init);
33
34	return fncache;
35}
36
37static bool lookup_fncache(const char *name, bool *res)
38{
39	long val;
40
41	if (!hashmap__find(fncache__get(), name, &val))
42		return false;
43
44	*res = (val != 0);
45	return true;
46}
47
48static void update_fncache(const char *name, bool res)
49{
50	char *old_key = NULL, *key = strdup(name);
51
52	if (key) {
53		hashmap__set(fncache__get(), key, res, &old_key, /*old_value*/NULL);
54		free(old_key);
55	}
56}
57
58/* No LRU, only use when bounded in some other way. */
59bool file_available(const char *name)
60{
61	bool res;
62
63	if (lookup_fncache(name, &res))
64		return res;
65	res = access(name, R_OK) == 0;
66	update_fncache(name, res);
67	return res;
68}