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, 57 insertions, 111 deletions

diff --git a/source3/smbd/vfs.c b/source3/smbd/vfs.c
index 628d2eec4b..45d0788117 100644
--- a/source3/smbd/vfs.c
+++ b/source3/smbd/vfs.c
@@ -731,152 +731,98 @@ int vfs_ChDir(connection_struct *conn, const char *path)
 	return(res);
 }
 
-/* number of list structures for a caching GetWd function. */
-#define MAX_GETWDCACHE (50)
-
-static struct {
-	SMB_DEV_T dev; /* These *must* be compatible with the types returned in a stat() call. */
-	SMB_INO_T inode; /* These *must* be compatible with the types returned in a stat() call. */
-	char *path; /* The pathname. */
-	bool valid;
-} ino_list[MAX_GETWDCACHE];
-
-extern bool use_getwd_cache;
-
-/****************************************************************************
- Prompte a ptr (to make it recently used)
-****************************************************************************/
-
-static void array_promote(char *array,int elsize,int element)
-{
-	char *p;
-	if (element == 0)
-		return;
-
-	p = (char *)SMB_MALLOC(elsize);
-
-	if (!p) {
-		DEBUG(5,("array_promote: malloc fail\n"));
-		return;
-	}
-
-	memcpy(p,array + element * elsize, elsize);
-	memmove(array + elsize,array,elsize*element);
-	memcpy(array,p,elsize);
-	SAFE_FREE(p);
-}
-
 /*******************************************************************
  Return the absolute current directory path - given a UNIX pathname.
  Note that this path is returned in DOS format, not UNIX
  format. Note this can be called with conn == NULL.
 ********************************************************************/
 
+struct getwd_cache_key {
+	SMB_DEV_T dev;
+	SMB_INO_T ino;
+};
+
 char *vfs_GetWd(TALLOC_CTX *ctx, connection_struct *conn)
 {
         char s[PATH_MAX+1];
-	static bool getwd_cache_init = False;
 	SMB_STRUCT_STAT st, st2;
-	int i;
-	char *ret = NULL;
+	char *result;
+	DATA_BLOB cache_value;
+	struct getwd_cache_key key;
 
 	*s = 0;
 
-	if (!use_getwd_cache) {
- nocache:
-		ret = SMB_VFS_GETWD(conn,s);
-		if (!ret) {
-			DEBUG(0,("vfs_GetWd: SMB_VFS_GETWD call failed, "
-				"errno %s\n",strerror(errno)));
-			return NULL;
-		}
-		return talloc_strdup(ctx, ret);
-	}
-
-	/* init the cache */
-	if (!getwd_cache_init) {
-		getwd_cache_init = True;
-		for (i=0;i<MAX_GETWDCACHE;i++) {
-			string_set(&ino_list[i].path,"");
-			ino_list[i].valid = False;
-		}
+	if (!lp_getwd_cache()) {
+		goto nocache;
 	}
 
-	/*  Get the inode of the current directory, if this doesn't work we're
-		in trouble :-) */
+	SET_STAT_INVALID(st);
 
 	if (SMB_VFS_STAT(conn, ".",&st) == -1) {
-		/* Known to fail for root: the directory may be
-		 * NFS-mounted and exported with root_squash (so has no root access). */
+		/*
+		 * Known to fail for root: the directory may be NFS-mounted
+		 * and exported with root_squash (so has no root access).
+		 */
 		DEBUG(1,("vfs_GetWd: couldn't stat \".\" error %s "
-			"(NFS problem ?)\n",
-			strerror(errno) ));
+			 "(NFS problem ?)\n", strerror(errno) ));
 		goto nocache;
 	}
 
+	ZERO_STRUCT(key); /* unlikely, but possible padding */
+	key.dev = st.st_dev;
+	key.ino = st.st_ino;
 
-	for (i=0; i<MAX_GETWDCACHE; i++) {
-		if (ino_list[i].valid) {
-
-			/*  If we have found an entry with a matching inode and dev number
-				then find the inode number for the directory in the cached string.
-				If this agrees with that returned by the stat for the current
-				directory then all is o.k. (but make sure it is a directory all
-				the same...) */
-
-			if (st.st_ino == ino_list[i].inode && st.st_dev == ino_list[i].dev) {
-				if (SMB_VFS_STAT(conn,ino_list[i].path,&st2) == 0) {
-					if (st.st_ino == st2.st_ino && st.st_dev == st2.st_dev &&
-							(st2.st_mode & S_IFMT) == S_IFDIR) {
+	if (!memcache_lookup(smbd_memcache(), GETWD_CACHE,
+			     data_blob_const(&key, sizeof(key)),
+			     &cache_value)) {
+		goto nocache;
+	}
 
-						ret = talloc_strdup(ctx,
-							ino_list[i].path);
+	SMB_ASSERT((cache_value.length > 0)
+		   && (cache_value.data[cache_value.length-1] == '\0'));
 
-						/* promote it for future use */
-						array_promote((char *)&ino_list[0],sizeof(ino_list[0]),i);
-						if (ret == NULL) {
-							errno = ENOMEM;
-						}
-						return ret;
-					} else {
-						/*  If the inode is different then something's changed,
-							scrub the entry and start from scratch. */
-						ino_list[i].valid = False;
-					}
-				}
-			}
+	if ((SMB_VFS_STAT(conn, (char *)cache_value.data, &st2) == 0)
+	    && (st.st_dev == st2.st_dev) && (st.st_ino == st2.st_ino)
+	    && (S_ISDIR(st.st_mode))) {
+		/*
+		 * Ok, we're done
+		 */
+		result = talloc_strdup(ctx, (char *)cache_value.data);
+		if (result == NULL) {
+			errno = ENOMEM;
 		}
+		return result;
 	}
 
-	/*  We don't have the information to hand so rely on traditional
-	 *  methods. The very slow getcwd, which spawns a process on some
-	 *  systems, or the not quite so bad getwd. */
+ nocache:
+
+	/*
+	 * We don't have the information to hand so rely on traditional
+	 * methods. The very slow getcwd, which spawns a process on some
+	 * systems, or the not quite so bad getwd.
+	 */
 
 	if (!SMB_VFS_GETWD(conn,s)) {
-		DEBUG(0,("vfs_GetWd: SMB_VFS_GETWD call failed, errno %s\n",
-				strerror(errno)));
-		return (NULL);
+		DEBUG(0, ("vfs_GetWd: SMB_VFS_GETWD call failed: %s\n",
+			  strerror(errno)));
+		return NULL;
 	}
 
-	ret = talloc_strdup(ctx,s);
-
-	DEBUG(5,("vfs_GetWd %s, inode %.0f, dev %.0f\n",
-				s,(double)st.st_ino,(double)st.st_dev));
-
-	/* add it to the cache */
-	i = MAX_GETWDCACHE - 1;
-	string_set(&ino_list[i].path,s);
-	ino_list[i].dev = st.st_dev;
-	ino_list[i].inode = st.st_ino;
-	ino_list[i].valid = True;
+	if (lp_getwd_cache() && VALID_STAT(st)) {
+		ZERO_STRUCT(key); /* unlikely, but possible padding */
+		key.dev = st.st_dev;
+		key.ino = st.st_ino;
 
-	/* put it at the top of the list */
-	array_promote((char *)&ino_list[0],sizeof(ino_list[0]),i);
+		memcache_add(smbd_memcache(), GETWD_CACHE,
+			     data_blob_const(&key, sizeof(key)),
+			     data_blob_const(s, strlen(s)+1));
+	}
 
-	if (ret == NULL) {
+	result = talloc_strdup(ctx, s);
+	if (result == NULL) {
 		errno = ENOMEM;
 	}
-	return ret;
+	return result;
 }
 
 /*******************************************************************