s3/smbd: open the share_info.tdb on startup instead of tconx

This is a small performance optimization.  Instead of opening the tdb
on every smb connection in the forked child process, we now open it in
the parent and share the fd.

This also reduces the total fd usage in the system.

source3/include/proto.h

@@ -721,6 +721,7 @@ struct named_mutex *grab_named_mutex(TALLOC_CTX *mem_ctx, const char *name,
 
 /* The following definitions come from lib/sharesec.c  */
 
+bool share_info_db_init(void);
 SEC_DESC *get_share_security_default( TALLOC_CTX *ctx, size_t *psize, uint32 def_access);
 SEC_DESC *get_share_security( TALLOC_CTX *ctx, const char *servicename,
 			      size_t *psize);

source3/lib/sharesec.c

@@ -37,7 +37,7 @@ static int delete_fn(struct db_record *rec, void *priv)
 	return 0;
 }
 
-static bool share_info_db_init(void)
+bool share_info_db_init(void)
 {
 	const char *vstring = "INFO/version";
 	int32 vers_id;

source3/smbd/server.c

@@ -1218,6 +1218,15 @@ extern void build_options(bool screen);
 		return -1;
 	}
 
+	/* Open the share_info.tdb here, so we don't have to open
+	   after the fork on every single connection.  This is a small
+	   performance improvment and reduces the total number of system
+	   fds used. */
+	if (!share_info_db_init()) {
+		DEBUG(0,("ERROR: failed to load share info db.\n"));
+		exit(1);
+	}
+
 	/* only start the background queue daemon if we are 
 	   running as a daemon -- bad things will happen if
 	   smbd is launched via inetd and we fork a copy of