LXR linux/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
   9struct fncache {
  10        struct hlist_node nd;
  11        bool res;
  12        char name[];
  13};
  14
  15#define FNHSIZE 61
  16
  17static struct hlist_head fncache_hash[FNHSIZE];
  18
  19unsigned 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
  27static 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
  41static 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. */
  54bool 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}
  64