Add a in-memory cache

This is a more general API that caches data with a LRU scheme. See
include/cache.h. No comments yet, I'm still working on it. But Jeremy has given
me a hint in one of his checkins that he would like to make use of this now.

The idea is that we get rid of all our silly little caches and merge them all
into one cache that we can then very easily trim, for example even with a
smbcontrol message if someone decides memory is tight. The main user is the
stat cache, this patch also converts the getwd cache. More caches to come.
(This used to be commit 7a911b35713538d82001a3c9f34152e293fe1943)

1 files changed, 19 insertions, 48 deletions

diff --git a/source3/smbd/mangle_hash2.c b/source3/smbd/mangle_hash2.c
index 7066c2a4e5..9643506aea 100644
--- a/source3/smbd/mangle_hash2.c
+++ b/source3/smbd/mangle_hash2.c
@@ -93,15 +93,6 @@ static unsigned char char_flags[256];
 */
 static unsigned mangle_prefix;
 
-/* we will use a very simple direct mapped prefix cache. The big
-   advantage of this cache structure is speed and low memory usage 
-
-   The cache is indexed by the low-order bits of the hash, and confirmed by
-   hashing the resulting cache entry to match the known hash
-*/
-static char **prefix_cache;
-static unsigned int *prefix_cache_hashes;
-
 /* these are the characters we use in the 8.3 hash. Must be 36 chars long */
 static const char *basechars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 static unsigned char base_reverse[256];
@@ -147,57 +138,39 @@ static unsigned int mangle_hash(const char *key, unsigned int length)
 	return value & ~0x80000000;  
 }
 
-/* 
-   initialise (ie. allocate) the prefix cache
- */
-static bool cache_init(void)
-{
-	if (prefix_cache) {
-		return True;
-	}
-
-	prefix_cache = SMB_CALLOC_ARRAY(char *,MANGLE_CACHE_SIZE);
-	if (!prefix_cache) {
-		return False;
-	}
-
-	prefix_cache_hashes = SMB_CALLOC_ARRAY(unsigned int, MANGLE_CACHE_SIZE);
-	if (!prefix_cache_hashes) {
-		SAFE_FREE(prefix_cache);
-		return False;
-	}
-
-	return True;
-}
-
 /*
   insert an entry into the prefix cache. The string might not be null
   terminated */
 static void cache_insert(const char *prefix, int length, unsigned int hash)
 {
-	int i = hash % MANGLE_CACHE_SIZE;
+	char *str = SMB_STRNDUP(prefix, length);
 
-	if (prefix_cache[i]) {
-		free(prefix_cache[i]);
+	if (str == NULL) {
+		return;
 	}
 
-	prefix_cache[i] = SMB_STRNDUP(prefix, length);
-	prefix_cache_hashes[i] = hash;
+	memcache_add(smbd_memcache(), MANGLE_HASH2_CACHE,
+		     data_blob_const(&hash, sizeof(hash)),
+		     data_blob_const(str, length+1));
+	SAFE_FREE(str);
 }
 
 /*
   lookup an entry in the prefix cache. Return NULL if not found.
 */
-static const char *cache_lookup(unsigned int hash)
+static char *cache_lookup(TALLOC_CTX *mem_ctx, unsigned int hash)
 {
-	int i = hash % MANGLE_CACHE_SIZE;
+	DATA_BLOB value;
 
-	if (!prefix_cache[i] || hash != prefix_cache_hashes[i]) {
+	if (!memcache_lookup(smbd_memcache(), MANGLE_HASH2_CACHE,
+			     data_blob_const(&hash, sizeof(hash)), &value)) {
 		return NULL;
 	}
 
-	/* yep, it matched */
-	return prefix_cache[i];
+	SMB_ASSERT((value.length > 0)
+		   && (value.data[value.length-1] == '\0'));
+
+	return talloc_strdup(mem_ctx, (char *)value.data);
 }
 
 
@@ -377,7 +350,7 @@ static bool lookup_name_from_8_3(TALLOC_CTX *ctx,
 {
 	unsigned int hash, multiplier;
 	unsigned int i;
-	const char *prefix;
+	char *prefix;
 	char extension[4];
 
 	*pp_out = NULL;
@@ -397,7 +370,7 @@ static bool lookup_name_from_8_3(TALLOC_CTX *ctx,
 	}
 
 	/* now look in the prefix cache for that hash */
-	prefix = cache_lookup(hash);
+	prefix = cache_lookup(ctx, hash);
 	if (!prefix) {
 		M_DEBUG(10,("lookup_name_from_8_3: %s -> %08X -> not found\n",
 					name, hash));
@@ -421,6 +394,8 @@ static bool lookup_name_from_8_3(TALLOC_CTX *ctx,
 		*pp_out = talloc_strdup(ctx, prefix);
 	}
 
+	TALLOC_FREE(prefix);
+
 	if (!pp_out) {
 		M_DEBUG(0,("talloc_fail"));
 		return False;
@@ -728,10 +703,6 @@ struct mangle_fns *mangle_hash2_init(void)
 	init_tables();
 	mangle_reset();
 
-	if (!cache_init()) {
-		return NULL;
-	}
-
 	return &mangle_fns;
 }