[RFC]Mesh: meshctl configuration output fails in gatt.c:pipe_write

[Steve Brown <sbrown@cortland.com>]

If the first command output in a new connection exceeds 20 bytes,
mesh_gatt_write sets the SAR to FIRST as the write_mtu is initially 0
and the default is GATT_MTU-3 (20).

When pipe_write gets called, a new larger write_mtu has been set, but
the SAR is still set to FIRST. It's assumed that data->gatt_len >
max_len. However, it's not which causes lots of bogus output.

I've added code to reset the SAR and length in acquire_write_reply in
case write_mtu might have changed. 

This seems to work, but I'm sure there is a better way.

Steve

---

[config: Target = 0100]# get-ttl
mesh_gatt_write: max_len:20 len:21 sar:0 write_mtu:0 write_io:(nil)
Characteristic property changed /org/bluez/hci0/dev_C9_63_A3_A6_CD_DA/service000a/char000b
AcquireWrite success: fd 8 MTU 69
pipe_write: len:21 max_len:65
GATT-TX:         40 f4 a8 fa b2 33 ac 51 80 ff 16 2e 74 b4 a0 bb
GATT-TX:         2f 2f 54 e2 96
GATT-TX: iov[0]:         40
GATT-TX: iov[1]:         f4 a8 fa b2 33 ac 51 80 ff 16 2e 74 b4 a0 bb 2f
GATT-TX: iov[1]:         2f 54 e2
GATT-TX: iov[0]:         80
GATT-TX: iov[1]:         00 00 fe ff ff ff fe ff ff ff fe ff ff ff fe ff
GATT-TX: iov[1]:         ff ff fe ff ff ff fe ff ff ff fe ff ff ff fe ff
GATT-TX: iov[1]:         ff ff 14 00 00 00 fe ff ff ff 01 00 00 00 70 15
GATT-TX: iov[1]:         d6 01 36 00 00 00 3e 00 00 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00
GATT-TX: iov[0]:         80
GATT-TX: iov[1]:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00 00 00 00 00 00 00 00 00 51 00 00 00 06 00 00
GATT-TX: iov[1]:         00 0c 98 d7 76 00 00 00 00 00 00 00 00 04 00 97
GATT-TX: iov[1]:         d7
GATT-TX: iov[0]:         80
GATT-TX: iov[1]:         76 c4 97 d7 00 00 00 00 30 00 00 00 b0 4d d4 01
GATT-TX: iov[1]:         e0 b6 dc 76 20 b6 dc 76 21 00 00 00 dc 97 d7 76
GATT-TX: iov[1]:         dc 97 d7 76 28 4e d4 01 20 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00 00 00 00 50 00 00 00 29 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00
GATT-TX: iov[0]:         c0
GATT-TX: iov[1]:         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
GATT-TX: iov[1]:         00

diff --git a/mesh/gatt.c b/mesh/gatt.c
index 001eb17a8..3f59268f2 100644
--- a/mesh/gatt.c
+++ b/mesh/gatt.c
@@ -358,6 +362,7 @@ static void acquire_write_reply(DBusMessage *message, void *user_data)
 	struct write_data *data = user_data;
 	DBusError error;
 	int fd;
+	uint8_t max_len;
 
 	dbus_error_init(&error);
 
@@ -383,6 +388,18 @@ static void acquire_write_reply(DBusMessage *message, void *user_data)
 
 	write_io = pipe_io_new(fd);
 
+	/* Reset type and length as write_mtu may have changed */
+	max_len = write_mtu ? write_mtu - 3 : GATT_MTU - 3;
+	data->gatt_data[0] &= GATT_TYPE_MASK;
+
+	if (max_len < data->gatt_len) {
+		data->iov.iov_len = max_len;
+		data->gatt_data[0] |= GATT_SAR_FIRST;
+	}
+
+	else
+		data->iov.iov_len = data->gatt_len;
+
 	pipe_write(write_io, data);
 }