tools/perf/util/fncache.c

   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((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((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->nd, &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))
  59                 return res;
  60         res = access(name, R_OK) == 0;
  61         update_fncache(name, res);
  62         return res;
  63 }