On Sun, 14 Mar 2010, Daniel Abraham wrote: > > You can probably use "sdptool search" to find specific services ok? > > Actually "sdptool" is just an example, the real problem is that when > BlueZ discovers that device, the SDP PDU truncation causes it to appear > to be profile-less, so I can't actively connect to any service, only > passively accept connections. Well, I'm not sure how BlueZ works in this regard but my question covers searching for a specific service in general - eg if you perform a ServiceSearchAttribute with a specific UUID and possibly a limited AttributeIDList then the response will be a whole lot smaller and probably fit into the L2CAP packet.. > > Although sdptool has no way to increase the "Incoming MTU" on the SDP > > connection, if you could work out how to do that it might allow more > > information to be received (in lib/sdp.c:sdp_connect_l2cap() set > > L2CAP_OPTIONS with imtu at some large number than 672, before the > > connect()) > > Although the PDU truncation is a bug not in BlueZ, I still think it > uncovers a point for improvement in BlueZ. > > Up until the truncation point, the PDU still contains 6-7 valid > attribute lists, which are discarded. Why not use them despite the > malformed PDU? The code that parses the response from the remote side is told that there are XXX bytes in the following data, but only yyy are in the packet.. what to do? Its obviously an error and you can't necessarily guess what the other side intended to send.. On the other hand, if BlueZ were to set the MaximiumAttributeByteCount to a lower value (eg see patch below), that might help your remote device to do the right thing.. if that works, the count could be calculated at runtime as MTU - 5(pdu hdr) - 2(attr count) - 17(max cont state) rather than using a fixed value. iain --- lib/sdp.c.orig 2010-03-14 19:56:19.000000000 +0000 +++ lib/sdp.c 2010-03-14 19:56:53.000000000 +0000 @@ -95,7 +95,7 @@ 0x80, 0x00, 0x00, 0x80, 0x5F, 0x9B, 0x34, 0xFB } }; -#define SDP_MAX_ATTR_LEN 65535 +#define SDP_MAX_ATTR_LEN 600 static sdp_data_t *sdp_copy_seq(sdp_data_t *data); static int sdp_attr_add_new_with_length(sdp_record_t *rec, -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
