1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* Manage a cache of file names' existence */ |
3 | #include <stdlib.h> |
4 | #include <unistd.h> |
5 | #include <string.h> |
6 | #include <linux/list.h> |
7 | #include "fncache.h" |
8 | |
9 | struct fncache { |
10 | struct hlist_node nd; |
11 | bool res; |
12 | char name[]; |
13 | }; |
14 | |
15 | #define FNHSIZE 61 |
16 | |
17 | static struct hlist_head fncache_hash[FNHSIZE]; |
18 | |
19 | unsigned shash(const unsigned char *s) |
20 | { |
21 | unsigned h = 0; |
22 | while (*s) |
23 | h = 65599 * h + *s++; |
24 | return h ^ (h >> 16); |
25 | } |
26 | |
27 | static bool lookup_fncache(const char *name, bool *res) |
28 | { |
29 | int h = shash(s: (const unsigned char *)name) % FNHSIZE; |
30 | struct fncache *n; |
31 | |
32 | hlist_for_each_entry(n, &fncache_hash[h], nd) { |
33 | if (!strcmp(n->name, name)) { |
34 | *res = n->res; |
35 | return true; |
36 | } |
37 | } |
38 | return false; |
39 | } |
40 | |
41 | static void update_fncache(const char *name, bool res) |
42 | { |
43 | struct fncache *n = malloc(sizeof(struct fncache) + strlen(name) + 1); |
44 | int h = shash(s: (const unsigned char *)name) % FNHSIZE; |
45 | |
46 | if (!n) |
47 | return; |
48 | strcpy(n->name, name); |
49 | n->res = res; |
50 | hlist_add_head(n: &n->nd, h: &fncache_hash[h]); |
51 | } |
52 | |
53 | /* No LRU, only use when bounded in some other way. */ |
54 | bool file_available(const char *name) |
55 | { |
56 | bool res; |
57 | |
58 | if (lookup_fncache(name, res: &res)) |
59 | return res; |
60 | res = access(name, R_OK) == 0; |
61 | update_fncache(name, res); |
62 | return res; |
63 | } |
64 | |