add support for error codes for CC_ERR

ChangeLog

@@ -37,6 +37,17 @@ Version NEXT
 	SCons now check if CC compiler works. We need SCons 1.1 or greater
 	  for building FSP now.
 	Large file support on Linux is now correctly detected.
+	Error codes added to CC_ERR command in PROTOCOL. It was long wished
+	  feature from ISV. Now there is standard way how to pass error codes
+	  from server to client. No such codes are defined yet, but you can
+	  use custom error codes in range 0xF000 - 0xFFFF. because no such
+	  codes are defined fspd do not sends them in error message, but it
+	  now correctly zeroes bb_pos field in CC_ERR reply to indicate
+	  that extended error code status is not attached to message. Old
+	  fspd versions left this field untouched - it will contain request
+	  bb_pos in most, but not all cases. Because we indicate size of
+	  extra data to be received, this extended error handling is
+	  compatible with "plain FSP over serial" standard.
 
 Version 2.8.1b25 - 10 Sep 2009
 	GNU autotools build system was entirely replaced by SCons

doc/PROTOCOL

@@ -252,9 +252,25 @@ CC_VERSION is recommended.
 		xtra data:     not used
 
 		reply
-		file position:  not used
+		file position:  size of extra data 
 		data:           ASCIIZ Error string
-		xtra data:	not used
+		xtra data:	not required
+                                word - error status code
+                
+                Error status codes are not currently standardised. If you
+                wish to participate in standardization process join FSP-devel
+                mailing list. For use in your own software use vendor-specific
+                error codes which have reserved range 0xF000 - 0xFFFF.
+
+                Compatibility
+
+                Support for sizing of extra data in reply was added
+                in fsp 2.8.1b26. Previous versions left this field
+                unchanged. In old versions it will most likely contain
+                file position used by requests but not always. In some
+                code paths in fspd it will be just uninitialized memory.
+                Its recommended to check if file position in reply is 2
+                otherwise it should be processed as containing zero.
 
  CC_GET_DIR  0x41		- get a directory listing
 

server/server.c

@@ -146,6 +146,7 @@ static void send_error (struct sockaddr_in * from, UBUF * ub, const char * msg)
   sz=strlen(msg)+1;
   memcpy(ub->buf,msg,sz);
   ub->cmd = CC_ERR;
+  BB_WRITE4(ub->bb_pos,0);
 
   server_reply(from,ub,sz,0);
 }