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util/disk_cache: use rand_xorshift128plus() to get our random int

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Otherwise for apps that don't seed the regular rand() we will always
remove old cache entries from the same dirs.

V2: assume bits returned by rand are independent uniformly distributed
    bits and grab our hex value without taking the modulus of the whole
    value, this also fixes a bug where 'f' was always missing.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
This commit is contained in:
Timothy Arceri
2017-03-21 19:35:22 +11:00
parent dd00a3c923
commit 6a9020f8dc
1 changed files with 10 additions and 8 deletions
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18
src/util/disk_cache.c
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@@ -41,6 +41,7 @@
#include "zlib.h" #include "zlib.h"
#include "util/crc32.h" #include "util/crc32.h"
#include "util/rand_xor.h"
#include "util/u_atomic.h" #include "util/u_atomic.h"
#include "util/u_queue.h" #include "util/u_queue.h"
#include "util/mesa-sha1.h" #include "util/mesa-sha1.h"
@@ -66,6 +67,9 @@ struct disk_cache {
/* Thread queue for compressing and writing cache entries to disk */ /* Thread queue for compressing and writing cache entries to disk */
struct util_queue cache_queue; struct util_queue cache_queue;
/* Seed for rand, which is used to pick a random directory */
uint64_t seed_xorshift128plus[2];
/* A pointer to the mmapped index file within the cache directory. */ /* A pointer to the mmapped index file within the cache directory. */
uint8_t *index_mmap; uint8_t *index_mmap;
size_t index_mmap_size; size_t index_mmap_size;
@@ -408,6 +412,9 @@ disk_cache_create(const char *gpu_name, const char *timestamp)
*/ */
util_queue_init(&cache->cache_queue, "disk_cache", 32, 1); util_queue_init(&cache->cache_queue, "disk_cache", 32, 1);
/* Seed our rand function */
s_rand_xorshift128plus(cache->seed_xorshift128plus, true);
ralloc_free(local); ralloc_free(local);
return cache; return cache;
@@ -613,23 +620,18 @@ is_two_character_sub_directory(const char *path, const struct stat *sb,
static void static void
evict_lru_item(struct disk_cache *cache) evict_lru_item(struct disk_cache *cache)
{ {
const char hex[] = "0123456789abcde";
char *dir_path; char *dir_path;
int a, b;
size_t size;
/* With a reasonably-sized, full cache, (and with keys generated /* With a reasonably-sized, full cache, (and with keys generated
* from a cryptographic hash), we can choose two random hex digits * from a cryptographic hash), we can choose two random hex digits
* and reasonably expect the directory to exist with a file in it. * and reasonably expect the directory to exist with a file in it.
* Provides pseudo-LRU eviction to reduce checking all cache files. * Provides pseudo-LRU eviction to reduce checking all cache files.
*/ */
a = rand() % 16; uint64_t rand64 = rand_xorshift128plus(cache->seed_xorshift128plus);
b = rand() % 16; if (asprintf(&dir_path, "%s/%02" PRIx64 , cache->path, rand64 & 0xff) < 0)
if (asprintf(&dir_path, "%s/%c%c", cache->path, hex[a], hex[b]) < 0)
return; return;
size = unlink_lru_file_from_directory(dir_path); size_t size = unlink_lru_file_from_directory(dir_path);
free(dir_path); free(dir_path);