[PATCH 1/5] TODO: remove 'fix MTU exchange' task

[PATCH 1/5] TODO: remove 'fix MTU exchange' task

[Bruna Moreira]

---
 TODO |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

diff --git a/TODO b/TODO
index 1120ad9..8b92808 100644
--- a/TODO
+++ b/TODO
@@ -136,11 +136,6 @@ ATT/GATT
   Priority: Medium
   Complexity: C2
 
-- GATT server: fix MTU exchange
-
-  Priority: Medium
-  Complexity: C2
-
 - Implement ATT PDU validation. Malformed PDUs can cause division by zero
   when decoding PDUs. A proper error PDU should be returned for this case.
   See decoding function in att.c file.
-- 
1.7.0.4

[PATCH 2/5] Add internal buffer to GAttrib struct

[Bruna Moreira]

The new buffer is allocated in g_attrib_new() and it will be used to
send/receive PDUs. The buffer size is the MTU read from L2CAP channel
limited to ATT_MAX_MTU. Functions to handle the buffer size were also
created.
---
 attrib/gattrib.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 attrib/gattrib.h |    3 +++
 2 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/attrib/gattrib.c b/attrib/gattrib.c
index 07e56de..ba168e7 100644
--- a/attrib/gattrib.c
+++ b/attrib/gattrib.c
@@ -40,6 +40,8 @@
 struct _GAttrib {
 	GIOChannel *io;
 	gint refs;
+	uint8_t *buf;
+	int buflen;
 	guint read_watch;
 	guint write_watch;
 	guint timeout_watch;
@@ -193,6 +195,8 @@ static void attrib_destroy(GAttrib *attrib)
 		g_io_channel_unref(attrib->io);
 	}
 
+	g_free(attrib->buf);
+
 	if (attrib->destroy)
 		attrib->destroy(attrib->destroy_user_data);
 
@@ -386,6 +390,7 @@ done:
 GAttrib *g_attrib_new(GIOChannel *io)
 {
 	struct _GAttrib *attrib;
+	uint16_t omtu;
 
 	g_io_channel_set_encoding(io, NULL, NULL);
 	g_io_channel_set_buffered(io, FALSE);
@@ -401,6 +406,17 @@ GAttrib *g_attrib_new(GIOChannel *io)
 			G_IO_IN | G_IO_HUP | G_IO_ERR | G_IO_NVAL,
 			received_data, attrib);
 
+	if (bt_io_get(attrib->io, BT_IO_L2CAP, NULL,
+			BT_IO_OPT_OMTU, &omtu,
+			BT_IO_OPT_INVALID)) {
+		if (omtu > ATT_MAX_MTU)
+			omtu = ATT_MAX_MTU;
+	} else
+		omtu = ATT_DEFAULT_LE_MTU;
+
+	attrib->buf = g_malloc0(omtu);
+	attrib->buflen = omtu;
+
 	return g_attrib_ref(attrib);
 }
 
@@ -504,6 +520,36 @@ gboolean g_attrib_set_debug(GAttrib *attrib,
 	return TRUE;
 }
 
+uint8_t *g_attrib_get_buffer(GAttrib *attrib, int *len)
+{
+	if (len == NULL)
+		return NULL;
+
+	*len = attrib->buflen;
+
+	return attrib->buf;
+}
+
+gboolean g_attrib_set_buffer(GAttrib *attrib, int mtu)
+{
+	if (mtu < ATT_DEFAULT_LE_MTU)
+		mtu = ATT_DEFAULT_LE_MTU;
+
+	if (mtu > ATT_MAX_MTU)
+		mtu = ATT_MAX_MTU;
+
+	if (!bt_io_set(attrib->io, BT_IO_L2CAP, NULL,
+			BT_IO_OPT_OMTU, mtu,
+			BT_IO_OPT_INVALID))
+		return FALSE;
+
+	attrib->buf = g_realloc(attrib->buf, mtu);
+
+	attrib->buflen = mtu;
+
+	return TRUE;
+}
+
 guint g_attrib_register(GAttrib *attrib, guint8 opcode,
 				GAttribNotifyFunc func, gpointer user_data,
 				GDestroyNotify notify)
diff --git a/attrib/gattrib.h b/attrib/gattrib.h
index f25208d..0211068 100644
--- a/attrib/gattrib.h
+++ b/attrib/gattrib.h
@@ -68,6 +68,9 @@ guint g_attrib_register(GAttrib *attrib, guint8 opcode,
 
 gboolean g_attrib_is_encrypted(GAttrib *attrib);
 
+uint8_t *g_attrib_get_buffer(GAttrib *attrib, int *len);
+gboolean g_attrib_set_buffer(GAttrib *attrib, int mtu);
+
 gboolean g_attrib_unregister(GAttrib *attrib, guint id);
 gboolean g_attrib_unregister_all(GAttrib *attrib);
 
-- 
1.7.0.4

Re: [PATCH 2/5] Add internal buffer to GAttrib struct

[Johan Hedberg]

Hi Bruna,

On Wed, Mar 16, 2011, Bruna Moreira wrote:
> +gboolean g_attrib_set_buffer(GAttrib *attrib, int mtu)
> +{
> +	if (mtu < ATT_DEFAULT_LE_MTU)
> +		mtu = ATT_DEFAULT_LE_MTU;
> +
> +	if (mtu > ATT_MAX_MTU)
> +		mtu = ATT_MAX_MTU;
> +
> +	if (!bt_io_set(attrib->io, BT_IO_L2CAP, NULL,
> +			BT_IO_OPT_OMTU, mtu,
> +			BT_IO_OPT_INVALID))
> +		return FALSE;
> +
> +	attrib->buf = g_realloc(attrib->buf, mtu);
> +
> +	attrib->buflen = mtu;
> +
> +	return TRUE;
> +}

Wouldn't g_attrib_set_mtu make more sense for the name of this function?
Since it's named symmetrically to the _get version one would expect it
to take a buffer as an input parameter, but it's not doing that.

Johan

Re: [PATCH 2/5] Add internal buffer to GAttrib struct

[Bruna Moreira]

On 3/17/11, Johan Hedberg <johan.hedberg@gmail.com> wrote:
> Hi Bruna,
>
> On Wed, Mar 16, 2011, Bruna Moreira wrote:
>> +gboolean g_attrib_set_buffer(GAttrib *attrib, int mtu)
>> +{
>> +	if (mtu < ATT_DEFAULT_LE_MTU)
>> +		mtu = ATT_DEFAULT_LE_MTU;
>> +
>> +	if (mtu > ATT_MAX_MTU)
>> +		mtu = ATT_MAX_MTU;
>> +
>> +	if (!bt_io_set(attrib->io, BT_IO_L2CAP, NULL,
>> +			BT_IO_OPT_OMTU, mtu,
>> +			BT_IO_OPT_INVALID))
>> +		return FALSE;
>> +
>> +	attrib->buf = g_realloc(attrib->buf, mtu);
>> +
>> +	attrib->buflen = mtu;
>> +
>> +	return TRUE;
>> +}
>
> Wouldn't g_attrib_set_mtu make more sense for the name of this function?
> Since it's named symmetrically to the _get version one would expect it
> to take a buffer as an input parameter, but it's not doing that.

Agreed. I will send a new updated series.

BR,
-- 
Bruna Moreira
Instituto Nokia de Tecnologia (INdT)
Manaus - Brazil

[PATCH 3/5] Use GAttrib buffer for ATT protocol PDUs

[Bruna Moreira]

Prior to this commit, there were local buffers inside GATT functions.
Now, a single buffer is used, to make sure the MTU limit is respected.
---
 attrib/gatt.c |  109 +++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 64 insertions(+), 45 deletions(-)

diff --git a/attrib/gatt.c b/attrib/gatt.c
index 32bd4a0..d3333fd 100644
--- a/attrib/gatt.c
+++ b/attrib/gatt.c
@@ -108,9 +108,9 @@ static void primary_by_uuid_cb(guint8 status, const guint8 *ipdu,
 	struct discover_primary *dp = user_data;
 	GSList *ranges, *last;
 	struct att_range *range;
-	uint8_t opdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
 	guint16 oplen;
-	int err = 0;
+	int err = 0, buflen;
 
 	if (status) {
 		err = status == ATT_ECODE_ATTR_NOT_FOUND ? 0 : status;
@@ -129,13 +129,14 @@ static void primary_by_uuid_cb(guint8 status, const guint8 *ipdu,
 	if (range->end == 0xffff)
 		goto done;
 
+	buf = g_attrib_get_buffer(dp->attrib, &buflen);
 	oplen = encode_discover_primary(range->end + 1, 0xffff, &dp->uuid,
-							opdu, sizeof(opdu));
+								buf, buflen);
 
 	if (oplen == 0)
 		goto done;
 
-	g_attrib_send(dp->attrib, 0, opdu[0], opdu, oplen, primary_by_uuid_cb,
+	g_attrib_send(dp->attrib, 0, buf[0], buf, oplen, primary_by_uuid_cb,
 								dp, NULL);
 	return;
 
@@ -196,12 +197,13 @@ static void primary_all_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	err = 0;
 
 	if (end != 0xffff) {
-		uint8_t opdu[ATT_DEFAULT_LE_MTU];
+		int buflen;
+		uint8_t *buf = g_attrib_get_buffer(dp->attrib, &buflen);
 		guint16 oplen = encode_discover_primary(end + 1, 0xffff, NULL,
-							opdu, sizeof(opdu));
+								buf, buflen);
 
-		g_attrib_send(dp->attrib, 0, opdu[0], opdu, oplen,
-						primary_all_cb, dp, NULL);
+		g_attrib_send(dp->attrib, 0, buf[0], buf, oplen, primary_all_cb,
+								dp, NULL);
 
 		return;
 	}
@@ -215,11 +217,12 @@ guint gatt_discover_primary(GAttrib *attrib, bt_uuid_t *uuid, gatt_cb_t func,
 							gpointer user_data)
 {
 	struct discover_primary *dp;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	GAttribResultFunc cb;
 	guint16 plen;
 
-	plen = encode_discover_primary(0x0001, 0xffff, uuid, pdu, sizeof(pdu));
+	plen = encode_discover_primary(0x0001, 0xffff, uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
@@ -237,7 +240,7 @@ guint gatt_discover_primary(GAttrib *attrib, bt_uuid_t *uuid, gatt_cb_t func,
 	} else
 		cb = primary_all_cb;
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, cb, dp, NULL);
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, cb, dp, NULL);
 }
 
 static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
@@ -246,7 +249,8 @@ static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	struct discover_char *dc = user_data;
 	struct att_data_list *list;
 	unsigned int i, err;
-	uint8_t opdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf;
 	guint16 oplen;
 	bt_uuid_t uuid;
 	uint16_t last = 0;
@@ -293,15 +297,17 @@ static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	err = 0;
 
 	if (last != 0) {
+		buf = g_attrib_get_buffer(dc->attrib, &buflen);
+
 		bt_uuid16_create(&uuid, GATT_CHARAC_UUID);
 
-		oplen = enc_read_by_type_req(last + 1, dc->end, &uuid, opdu,
-								sizeof(opdu));
+		oplen = enc_read_by_type_req(last + 1, dc->end, &uuid, buf,
+									buflen);
 
 		if (oplen == 0)
 			return;
 
-		g_attrib_send(dc->attrib, 0, opdu[0], opdu, oplen,
+		g_attrib_send(dc->attrib, 0, buf[0], buf, oplen,
 						char_discovered_cb, dc, NULL);
 
 		return;
@@ -315,14 +321,15 @@ done:
 guint gatt_discover_char(GAttrib *attrib, uint16_t start, uint16_t end,
 					gatt_cb_t func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	struct discover_char *dc;
 	guint16 plen;
 	bt_uuid_t uuid;
 
 	bt_uuid16_create(&uuid, GATT_CHARAC_UUID);
 
-	plen = enc_read_by_type_req(start, end, &uuid, pdu, sizeof(pdu));
+	plen = enc_read_by_type_req(start, end, &uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
@@ -335,7 +342,7 @@ guint gatt_discover_char(GAttrib *attrib, uint16_t start, uint16_t end,
 	dc->user_data = user_data;
 	dc->end = end;
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, char_discovered_cb,
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, char_discovered_cb,
 								dc, NULL);
 }
 
@@ -343,15 +350,16 @@ guint gatt_read_char_by_uuid(GAttrib *attrib, uint16_t start, uint16_t end,
 					bt_uuid_t *uuid, GAttribResultFunc func,
 					gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	guint16 plen;
 
-	plen = enc_read_by_type_req(start, end, uuid, pdu, sizeof(pdu));
+	plen = enc_read_by_type_req(start, end, uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
 	return g_attrib_send(attrib, 0, ATT_OP_READ_BY_TYPE_REQ,
-					pdu, plen, func, user_data, NULL);
+					buf, plen, func, user_data, NULL);
 }
 
 struct read_long_data {
@@ -382,7 +390,8 @@ static void read_blob_helper(guint8 status, const guint8 *rpdu, guint16 rlen,
 							gpointer user_data)
 {
 	struct read_long_data *long_read = user_data;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint8 *tmp;
 	guint16 plen;
 	guint id;
@@ -403,13 +412,14 @@ static void read_blob_helper(guint8 status, const guint8 *rpdu, guint16 rlen,
 	long_read->buffer = tmp;
 	long_read->size += rlen - 1;
 
-	if (rlen < ATT_DEFAULT_LE_MTU)
+	buf = g_attrib_get_buffer(long_read->attrib, &buflen);
+	if (rlen < buflen)
 		goto done;
 
 	plen = enc_read_blob_req(long_read->handle, long_read->size - 1,
-							pdu, sizeof(pdu));
+								buf, buflen);
 	id = g_attrib_send(long_read->attrib, long_read->id,
-				ATT_OP_READ_BLOB_REQ, pdu, plen,
+				ATT_OP_READ_BLOB_REQ, buf, plen,
 				read_blob_helper, long_read, read_long_destroy);
 
 	if (id != 0) {
@@ -428,11 +438,12 @@ static void read_char_helper(guint8 status, const guint8 *rpdu,
 					guint16 rlen, gpointer user_data)
 {
 	struct read_long_data *long_read = user_data;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(long_read->attrib, &buflen);
 	guint16 plen;
 	guint id;
 
-	if (status != 0 || rlen < ATT_DEFAULT_LE_MTU)
+	if (status != 0 || rlen < buflen)
 		goto done;
 
 	long_read->buffer = g_malloc(rlen);
@@ -443,9 +454,9 @@ static void read_char_helper(guint8 status, const guint8 *rpdu,
 	memcpy(long_read->buffer, rpdu, rlen);
 	long_read->size = rlen;
 
-	plen = enc_read_blob_req(long_read->handle, rlen - 1, pdu, sizeof(pdu));
+	plen = enc_read_blob_req(long_read->handle, rlen - 1, buf, buflen);
 	id = g_attrib_send(long_read->attrib, long_read->id,
-			ATT_OP_READ_BLOB_REQ, pdu, plen, read_blob_helper,
+			ATT_OP_READ_BLOB_REQ, buf, plen, read_blob_helper,
 			long_read, read_long_destroy);
 
 	if (id != 0) {
@@ -462,7 +473,8 @@ done:
 guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 				GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 	guint id;
 	struct read_long_data *long_read;
@@ -477,14 +489,15 @@ guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 	long_read->user_data = user_data;
 	long_read->handle = handle;
 
+	buf = g_attrib_get_buffer(attrib, &buflen);
 	if (offset > 0) {
-		plen = enc_read_blob_req(long_read->handle, offset, pdu,
-								sizeof(pdu));
-		id = g_attrib_send(attrib, 0, ATT_OP_READ_BLOB_REQ, pdu, plen,
+		plen = enc_read_blob_req(long_read->handle, offset, buf,
+									buflen);
+		id = g_attrib_send(attrib, 0, ATT_OP_READ_BLOB_REQ, buf, plen,
 				read_blob_helper, long_read, read_long_destroy);
 	} else {
-		plen = enc_read_req(handle, pdu, sizeof(pdu));
-		id = g_attrib_send(attrib, 0, ATT_OP_READ_REQ, pdu, plen,
+		plen = enc_read_req(handle, buf, buflen);
+		id = g_attrib_send(attrib, 0, ATT_OP_READ_REQ, buf, plen,
 				read_char_helper, long_read, read_long_destroy);
 	}
 
@@ -501,39 +514,45 @@ guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 guint gatt_write_char(GAttrib *attrib, uint16_t handle, uint8_t *value,
 			int vlen, GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
+	buf = g_attrib_get_buffer(attrib, &buflen);
 	if (func)
-		plen = enc_write_req(handle, value, vlen, pdu, sizeof(pdu));
+		plen = enc_write_req(handle, value, vlen, buf, buflen);
 	else
-		plen = enc_write_cmd(handle, value, vlen, pdu, sizeof(pdu));
+		plen = enc_write_cmd(handle, value, vlen, buf, buflen);
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, func,
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, func,
 							user_data, NULL);
 }
 
 guint gatt_find_info(GAttrib *attrib, uint16_t start, uint16_t end,
 				GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
-	plen = enc_find_info_req(start, end, pdu, sizeof(pdu));
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_find_info_req(start, end, buf, buflen);
 	if (plen == 0)
 		return 0;
 
-	return g_attrib_send(attrib, 0, ATT_OP_FIND_INFO_REQ, pdu, plen, func,
+	return g_attrib_send(attrib, 0, ATT_OP_FIND_INFO_REQ, buf, plen, func,
 							user_data, NULL);
 }
 
 guint gatt_write_cmd(GAttrib *attrib, uint16_t handle, uint8_t *value, int vlen,
 				GDestroyNotify notify, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
-	plen = enc_write_cmd(handle, value, vlen, pdu, sizeof(pdu));
-	return g_attrib_send(attrib, 0, ATT_OP_WRITE_CMD, pdu, plen, NULL,
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_write_cmd(handle, value, vlen, buf, buflen);
+	return g_attrib_send(attrib, 0, ATT_OP_WRITE_CMD, buf, plen, NULL,
 							user_data, notify);
 }
-- 
1.7.0.4

[PATCH 4/5] Add Exchange MTU operation in GATT library

[Bruna Moreira]

---
 attrib/gatt.c |   13 +++++++++++++
 attrib/gatt.h |    3 +++
 2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/attrib/gatt.c b/attrib/gatt.c
index d3333fd..a9863e3 100644
--- a/attrib/gatt.c
+++ b/attrib/gatt.c
@@ -528,6 +528,19 @@ guint gatt_write_char(GAttrib *attrib, uint16_t handle, uint8_t *value,
 							user_data, NULL);
 }
 
+guint gatt_exchange_mtu(GAttrib *attrib, uint16_t mtu, GAttribResultFunc func,
+							gpointer user_data)
+{
+	uint8_t *buf;
+	int buflen;
+	guint16 plen;
+
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_mtu_req(mtu, buf, buflen);
+	return g_attrib_send(attrib, 0, ATT_OP_MTU_REQ, buf, plen, func,
+							user_data, NULL);
+}
+
 guint gatt_find_info(GAttrib *attrib, uint16_t start, uint16_t end,
 				GAttribResultFunc func, gpointer user_data)
 {
diff --git a/attrib/gatt.h b/attrib/gatt.h
index 730de7e..347c1a6 100644
--- a/attrib/gatt.h
+++ b/attrib/gatt.h
@@ -47,3 +47,6 @@ guint gatt_write_cmd(GAttrib *attrib, uint16_t handle, uint8_t *value, int vlen,
 guint gatt_read_char_by_uuid(GAttrib *attrib, uint16_t start, uint16_t end,
 				bt_uuid_t *uuid, GAttribResultFunc func,
 				gpointer user_data);
+
+guint gatt_exchange_mtu(GAttrib *attrib, uint16_t mtu, GAttribResultFunc func,
+							gpointer user_data);
-- 
1.7.0.4

[PATCH 5/5] Add Exchange MTU in interactive gatttool

[Bruna Moreira]

---
 attrib/interactive.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 62 insertions(+), 0 deletions(-)

diff --git a/attrib/interactive.c b/attrib/interactive.c
index b32e9e7..38fc75a 100644
--- a/attrib/interactive.c
+++ b/attrib/interactive.c
@@ -362,6 +362,7 @@ static void cmd_disconnect(int argcp, char **argvp)
 
 	g_attrib_unref(attrib);
 	attrib = NULL;
+	opt_mtu = 0;
 
 	g_io_channel_shutdown(iochannel, FALSE, NULL);
 	g_io_channel_unref(iochannel);
@@ -642,6 +643,65 @@ static void cmd_sec_level(int argcp, char **argvp)
 	}
 }
 
+static void exchange_mtu_cb(guint8 status, const guint8 *pdu, guint16 plen,
+							gpointer user_data)
+{
+	uint16_t mtu;
+
+	if (status != 0) {
+		printf("Exchange MTU Request failed: %s\n",
+							att_ecode2str(status));
+		return;
+	}
+
+	if (!dec_mtu_resp(pdu, plen, &mtu)) {
+		printf("Protocol error\n");
+		return;
+	}
+
+	mtu = MIN(mtu, opt_mtu);
+	/* Set new value for MTU in client */
+	if (g_attrib_set_buffer(attrib, mtu))
+		printf("MTU was exchanged successfully: %d\n", mtu);
+	else
+		printf("Error exchanging MTU\n");
+}
+
+static void cmd_mtu(int argcp, char **argvp)
+{
+	if (conn_state != STATE_CONNECTED) {
+		printf("Command failed: not connected.\n");
+		return;
+	}
+
+	if (opt_psm) {
+		printf("Command failed: operation is only available for LE"
+							" transport.\n");
+		return;
+	}
+
+	if (argcp < 2) {
+		printf("Usage: mtu <value>\n");
+		return;
+	}
+
+	if (opt_mtu) {
+		printf("Command failed: MTU exchange can only occur once per"
+							" connection.\n");
+		return;
+	}
+
+	errno = 0;
+	opt_mtu = strtoll(argvp[1], NULL, 0);
+	if (errno != 0 || opt_mtu < ATT_DEFAULT_LE_MTU) {
+		printf("Invalid value. Minimum MTU size is %d\n",
+							ATT_DEFAULT_LE_MTU);
+		return;
+	}
+
+	gatt_exchange_mtu(attrib, opt_mtu, exchange_mtu_cb, NULL);
+}
+
 static struct {
 	const char *cmd;
 	void (*func)(int argcp, char **argvp);
@@ -672,6 +732,8 @@ static struct {
 		"Characteristic Value Write (No response)" },
 	{ "sec-level",		cmd_sec_level,	"[low | medium | high]",
 		"Set security level. Default: low" },
+	{ "mtu",		cmd_mtu,	"<value>",
+		"Exchange MTU for GATT/ATT" },
 	{ NULL, NULL, NULL}
 };
 
-- 
1.7.0.4

[PATCHv2 1/5] TODO: remove 'fix MTU exchange' task

[Bruna Moreira]

---
 TODO |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

diff --git a/TODO b/TODO
index f49a9c4..588d9f6 100644
--- a/TODO
+++ b/TODO
@@ -130,11 +130,6 @@ ATT/GATT
   Priority: Medium
   Complexity: C2
 
-- GATT server: fix MTU exchange
-
-  Priority: Medium
-  Complexity: C2
-
 - Implement ATT PDU validation. Malformed PDUs can cause division by zero
   when decoding PDUs. A proper error PDU should be returned for this case.
   See decoding function in att.c file.
-- 
1.7.0.4

Re: [PATCHv2 1/5] TODO: remove 'fix MTU exchange' task

[Johan Hedberg]

Hi Bruna,

On Thu, Mar 17, 2011, Bruna Moreira wrote:
> ---
>  TODO |    5 -----
>  1 files changed, 0 insertions(+), 5 deletions(-)

All five patches have now been pushed upstream. Thanks.

Johan

[PATCHv2 2/5] Add internal buffer to GAttrib struct

[Bruna Moreira]

The new buffer is allocated in g_attrib_new() and it will be used to
send/receive PDUs. The buffer size is the MTU read from L2CAP channel
limited to ATT_MAX_MTU. Functions to handle the buffer size were also
created.
---
 attrib/gattrib.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 attrib/gattrib.h |    3 +++
 2 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/attrib/gattrib.c b/attrib/gattrib.c
index 07e56de..290cd96 100644
--- a/attrib/gattrib.c
+++ b/attrib/gattrib.c
@@ -40,6 +40,8 @@
 struct _GAttrib {
 	GIOChannel *io;
 	gint refs;
+	uint8_t *buf;
+	int buflen;
 	guint read_watch;
 	guint write_watch;
 	guint timeout_watch;
@@ -193,6 +195,8 @@ static void attrib_destroy(GAttrib *attrib)
 		g_io_channel_unref(attrib->io);
 	}
 
+	g_free(attrib->buf);
+
 	if (attrib->destroy)
 		attrib->destroy(attrib->destroy_user_data);
 
@@ -386,6 +390,7 @@ done:
 GAttrib *g_attrib_new(GIOChannel *io)
 {
 	struct _GAttrib *attrib;
+	uint16_t omtu;
 
 	g_io_channel_set_encoding(io, NULL, NULL);
 	g_io_channel_set_buffered(io, FALSE);
@@ -401,6 +406,17 @@ GAttrib *g_attrib_new(GIOChannel *io)
 			G_IO_IN | G_IO_HUP | G_IO_ERR | G_IO_NVAL,
 			received_data, attrib);
 
+	if (bt_io_get(attrib->io, BT_IO_L2CAP, NULL,
+			BT_IO_OPT_OMTU, &omtu,
+			BT_IO_OPT_INVALID)) {
+		if (omtu > ATT_MAX_MTU)
+			omtu = ATT_MAX_MTU;
+	} else
+		omtu = ATT_DEFAULT_LE_MTU;
+
+	attrib->buf = g_malloc0(omtu);
+	attrib->buflen = omtu;
+
 	return g_attrib_ref(attrib);
 }
 
@@ -504,6 +520,36 @@ gboolean g_attrib_set_debug(GAttrib *attrib,
 	return TRUE;
 }
 
+uint8_t *g_attrib_get_buffer(GAttrib *attrib, int *len)
+{
+	if (len == NULL)
+		return NULL;
+
+	*len = attrib->buflen;
+
+	return attrib->buf;
+}
+
+gboolean g_attrib_set_mtu(GAttrib *attrib, int mtu)
+{
+	if (mtu < ATT_DEFAULT_LE_MTU)
+		mtu = ATT_DEFAULT_LE_MTU;
+
+	if (mtu > ATT_MAX_MTU)
+		mtu = ATT_MAX_MTU;
+
+	if (!bt_io_set(attrib->io, BT_IO_L2CAP, NULL,
+			BT_IO_OPT_OMTU, mtu,
+			BT_IO_OPT_INVALID))
+		return FALSE;
+
+	attrib->buf = g_realloc(attrib->buf, mtu);
+
+	attrib->buflen = mtu;
+
+	return TRUE;
+}
+
 guint g_attrib_register(GAttrib *attrib, guint8 opcode,
 				GAttribNotifyFunc func, gpointer user_data,
 				GDestroyNotify notify)
diff --git a/attrib/gattrib.h b/attrib/gattrib.h
index f25208d..4c49879 100644
--- a/attrib/gattrib.h
+++ b/attrib/gattrib.h
@@ -68,6 +68,9 @@ guint g_attrib_register(GAttrib *attrib, guint8 opcode,
 
 gboolean g_attrib_is_encrypted(GAttrib *attrib);
 
+uint8_t *g_attrib_get_buffer(GAttrib *attrib, int *len);
+gboolean g_attrib_set_mtu(GAttrib *attrib, int mtu);
+
 gboolean g_attrib_unregister(GAttrib *attrib, guint id);
 gboolean g_attrib_unregister_all(GAttrib *attrib);
 
-- 
1.7.0.4

[PATCHv2 3/5] Use GAttrib buffer for ATT protocol PDUs

[Bruna Moreira]

Prior to this commit, there were local buffers inside GATT functions.
Now, a single buffer is used, to make sure the MTU limit is respected.
---
 attrib/gatt.c |  109 +++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 64 insertions(+), 45 deletions(-)

diff --git a/attrib/gatt.c b/attrib/gatt.c
index 1cd651c..28654af 100644
--- a/attrib/gatt.c
+++ b/attrib/gatt.c
@@ -109,9 +109,9 @@ static void primary_by_uuid_cb(guint8 status, const guint8 *ipdu,
 	struct discover_primary *dp = user_data;
 	GSList *ranges, *last;
 	struct att_range *range;
-	uint8_t opdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
 	guint16 oplen;
-	int err = 0;
+	int err = 0, buflen;
 
 	if (status) {
 		err = status == ATT_ECODE_ATTR_NOT_FOUND ? 0 : status;
@@ -130,13 +130,14 @@ static void primary_by_uuid_cb(guint8 status, const guint8 *ipdu,
 	if (range->end == 0xffff)
 		goto done;
 
+	buf = g_attrib_get_buffer(dp->attrib, &buflen);
 	oplen = encode_discover_primary(range->end + 1, 0xffff, &dp->uuid,
-							opdu, sizeof(opdu));
+								buf, buflen);
 
 	if (oplen == 0)
 		goto done;
 
-	g_attrib_send(dp->attrib, 0, opdu[0], opdu, oplen, primary_by_uuid_cb,
+	g_attrib_send(dp->attrib, 0, buf[0], buf, oplen, primary_by_uuid_cb,
 								dp, NULL);
 	return;
 
@@ -197,12 +198,13 @@ static void primary_all_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	err = 0;
 
 	if (end != 0xffff) {
-		uint8_t opdu[ATT_DEFAULT_LE_MTU];
+		int buflen;
+		uint8_t *buf = g_attrib_get_buffer(dp->attrib, &buflen);
 		guint16 oplen = encode_discover_primary(end + 1, 0xffff, NULL,
-							opdu, sizeof(opdu));
+								buf, buflen);
 
-		g_attrib_send(dp->attrib, 0, opdu[0], opdu, oplen,
-						primary_all_cb, dp, NULL);
+		g_attrib_send(dp->attrib, 0, buf[0], buf, oplen, primary_all_cb,
+								dp, NULL);
 
 		return;
 	}
@@ -216,11 +218,12 @@ guint gatt_discover_primary(GAttrib *attrib, bt_uuid_t *uuid, gatt_cb_t func,
 							gpointer user_data)
 {
 	struct discover_primary *dp;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	GAttribResultFunc cb;
 	guint16 plen;
 
-	plen = encode_discover_primary(0x0001, 0xffff, uuid, pdu, sizeof(pdu));
+	plen = encode_discover_primary(0x0001, 0xffff, uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
@@ -238,7 +241,7 @@ guint gatt_discover_primary(GAttrib *attrib, bt_uuid_t *uuid, gatt_cb_t func,
 	} else
 		cb = primary_all_cb;
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, cb, dp, NULL);
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, cb, dp, NULL);
 }
 
 static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
@@ -247,7 +250,8 @@ static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	struct discover_char *dc = user_data;
 	struct att_data_list *list;
 	unsigned int i, err;
-	uint8_t opdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf;
 	guint16 oplen;
 	bt_uuid_t uuid;
 	uint16_t last = 0;
@@ -297,15 +301,17 @@ static void char_discovered_cb(guint8 status, const guint8 *ipdu, guint16 iplen,
 	err = 0;
 
 	if (last != 0) {
+		buf = g_attrib_get_buffer(dc->attrib, &buflen);
+
 		bt_uuid16_create(&uuid, GATT_CHARAC_UUID);
 
-		oplen = enc_read_by_type_req(last + 1, dc->end, &uuid, opdu,
-								sizeof(opdu));
+		oplen = enc_read_by_type_req(last + 1, dc->end, &uuid, buf,
+									buflen);
 
 		if (oplen == 0)
 			return;
 
-		g_attrib_send(dc->attrib, 0, opdu[0], opdu, oplen,
+		g_attrib_send(dc->attrib, 0, buf[0], buf, oplen,
 						char_discovered_cb, dc, NULL);
 
 		return;
@@ -320,14 +326,15 @@ guint gatt_discover_char(GAttrib *attrib, uint16_t start, uint16_t end,
 						bt_uuid_t *uuid, gatt_cb_t func,
 						gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	struct discover_char *dc;
 	bt_uuid_t type_uuid;
 	guint16 plen;
 
 	bt_uuid16_create(&type_uuid, GATT_CHARAC_UUID);
 
-	plen = enc_read_by_type_req(start, end, &type_uuid, pdu, sizeof(pdu));
+	plen = enc_read_by_type_req(start, end, &type_uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
@@ -341,7 +348,7 @@ guint gatt_discover_char(GAttrib *attrib, uint16_t start, uint16_t end,
 	dc->end = end;
 	dc->uuid = g_memdup(uuid, sizeof(bt_uuid_t));
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, char_discovered_cb,
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, char_discovered_cb,
 								dc, NULL);
 }
 
@@ -349,15 +356,16 @@ guint gatt_read_char_by_uuid(GAttrib *attrib, uint16_t start, uint16_t end,
 					bt_uuid_t *uuid, GAttribResultFunc func,
 					gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(attrib, &buflen);
 	guint16 plen;
 
-	plen = enc_read_by_type_req(start, end, uuid, pdu, sizeof(pdu));
+	plen = enc_read_by_type_req(start, end, uuid, buf, buflen);
 	if (plen == 0)
 		return 0;
 
 	return g_attrib_send(attrib, 0, ATT_OP_READ_BY_TYPE_REQ,
-					pdu, plen, func, user_data, NULL);
+					buf, plen, func, user_data, NULL);
 }
 
 struct read_long_data {
@@ -388,7 +396,8 @@ static void read_blob_helper(guint8 status, const guint8 *rpdu, guint16 rlen,
 							gpointer user_data)
 {
 	struct read_long_data *long_read = user_data;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint8 *tmp;
 	guint16 plen;
 	guint id;
@@ -409,13 +418,14 @@ static void read_blob_helper(guint8 status, const guint8 *rpdu, guint16 rlen,
 	long_read->buffer = tmp;
 	long_read->size += rlen - 1;
 
-	if (rlen < ATT_DEFAULT_LE_MTU)
+	buf = g_attrib_get_buffer(long_read->attrib, &buflen);
+	if (rlen < buflen)
 		goto done;
 
 	plen = enc_read_blob_req(long_read->handle, long_read->size - 1,
-							pdu, sizeof(pdu));
+								buf, buflen);
 	id = g_attrib_send(long_read->attrib, long_read->id,
-				ATT_OP_READ_BLOB_REQ, pdu, plen,
+				ATT_OP_READ_BLOB_REQ, buf, plen,
 				read_blob_helper, long_read, read_long_destroy);
 
 	if (id != 0) {
@@ -434,11 +444,12 @@ static void read_char_helper(guint8 status, const guint8 *rpdu,
 					guint16 rlen, gpointer user_data)
 {
 	struct read_long_data *long_read = user_data;
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	int buflen;
+	uint8_t *buf = g_attrib_get_buffer(long_read->attrib, &buflen);
 	guint16 plen;
 	guint id;
 
-	if (status != 0 || rlen < ATT_DEFAULT_LE_MTU)
+	if (status != 0 || rlen < buflen)
 		goto done;
 
 	long_read->buffer = g_malloc(rlen);
@@ -449,9 +460,9 @@ static void read_char_helper(guint8 status, const guint8 *rpdu,
 	memcpy(long_read->buffer, rpdu, rlen);
 	long_read->size = rlen;
 
-	plen = enc_read_blob_req(long_read->handle, rlen - 1, pdu, sizeof(pdu));
+	plen = enc_read_blob_req(long_read->handle, rlen - 1, buf, buflen);
 	id = g_attrib_send(long_read->attrib, long_read->id,
-			ATT_OP_READ_BLOB_REQ, pdu, plen, read_blob_helper,
+			ATT_OP_READ_BLOB_REQ, buf, plen, read_blob_helper,
 			long_read, read_long_destroy);
 
 	if (id != 0) {
@@ -468,7 +479,8 @@ done:
 guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 				GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 	guint id;
 	struct read_long_data *long_read;
@@ -483,14 +495,15 @@ guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 	long_read->user_data = user_data;
 	long_read->handle = handle;
 
+	buf = g_attrib_get_buffer(attrib, &buflen);
 	if (offset > 0) {
-		plen = enc_read_blob_req(long_read->handle, offset, pdu,
-								sizeof(pdu));
-		id = g_attrib_send(attrib, 0, ATT_OP_READ_BLOB_REQ, pdu, plen,
+		plen = enc_read_blob_req(long_read->handle, offset, buf,
+									buflen);
+		id = g_attrib_send(attrib, 0, ATT_OP_READ_BLOB_REQ, buf, plen,
 				read_blob_helper, long_read, read_long_destroy);
 	} else {
-		plen = enc_read_req(handle, pdu, sizeof(pdu));
-		id = g_attrib_send(attrib, 0, ATT_OP_READ_REQ, pdu, plen,
+		plen = enc_read_req(handle, buf, buflen);
+		id = g_attrib_send(attrib, 0, ATT_OP_READ_REQ, buf, plen,
 				read_char_helper, long_read, read_long_destroy);
 	}
 
@@ -507,39 +520,45 @@ guint gatt_read_char(GAttrib *attrib, uint16_t handle, uint16_t offset,
 guint gatt_write_char(GAttrib *attrib, uint16_t handle, uint8_t *value,
 			int vlen, GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
+	buf = g_attrib_get_buffer(attrib, &buflen);
 	if (func)
-		plen = enc_write_req(handle, value, vlen, pdu, sizeof(pdu));
+		plen = enc_write_req(handle, value, vlen, buf, buflen);
 	else
-		plen = enc_write_cmd(handle, value, vlen, pdu, sizeof(pdu));
+		plen = enc_write_cmd(handle, value, vlen, buf, buflen);
 
-	return g_attrib_send(attrib, 0, pdu[0], pdu, plen, func,
+	return g_attrib_send(attrib, 0, buf[0], buf, plen, func,
 							user_data, NULL);
 }
 
 guint gatt_find_info(GAttrib *attrib, uint16_t start, uint16_t end,
 				GAttribResultFunc func, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
-	plen = enc_find_info_req(start, end, pdu, sizeof(pdu));
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_find_info_req(start, end, buf, buflen);
 	if (plen == 0)
 		return 0;
 
-	return g_attrib_send(attrib, 0, ATT_OP_FIND_INFO_REQ, pdu, plen, func,
+	return g_attrib_send(attrib, 0, ATT_OP_FIND_INFO_REQ, buf, plen, func,
 							user_data, NULL);
 }
 
 guint gatt_write_cmd(GAttrib *attrib, uint16_t handle, uint8_t *value, int vlen,
 				GDestroyNotify notify, gpointer user_data)
 {
-	uint8_t pdu[ATT_DEFAULT_LE_MTU];
+	uint8_t *buf;
+	int buflen;
 	guint16 plen;
 
-	plen = enc_write_cmd(handle, value, vlen, pdu, sizeof(pdu));
-	return g_attrib_send(attrib, 0, ATT_OP_WRITE_CMD, pdu, plen, NULL,
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_write_cmd(handle, value, vlen, buf, buflen);
+	return g_attrib_send(attrib, 0, ATT_OP_WRITE_CMD, buf, plen, NULL,
 							user_data, notify);
 }
-- 
1.7.0.4

[PATCHv2 4/5] Add Exchange MTU operation in GATT library

[Bruna Moreira]

---
 attrib/gatt.c |   13 +++++++++++++
 attrib/gatt.h |    3 +++
 2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/attrib/gatt.c b/attrib/gatt.c
index 28654af..0b69daf 100644
--- a/attrib/gatt.c
+++ b/attrib/gatt.c
@@ -534,6 +534,19 @@ guint gatt_write_char(GAttrib *attrib, uint16_t handle, uint8_t *value,
 							user_data, NULL);
 }
 
+guint gatt_exchange_mtu(GAttrib *attrib, uint16_t mtu, GAttribResultFunc func,
+							gpointer user_data)
+{
+	uint8_t *buf;
+	int buflen;
+	guint16 plen;
+
+	buf = g_attrib_get_buffer(attrib, &buflen);
+	plen = enc_mtu_req(mtu, buf, buflen);
+	return g_attrib_send(attrib, 0, ATT_OP_MTU_REQ, buf, plen, func,
+							user_data, NULL);
+}
+
 guint gatt_find_info(GAttrib *attrib, uint16_t start, uint16_t end,
 				GAttribResultFunc func, gpointer user_data)
 {
diff --git a/attrib/gatt.h b/attrib/gatt.h
index c6d3843..221d94d 100644
--- a/attrib/gatt.h
+++ b/attrib/gatt.h
@@ -48,3 +48,6 @@ guint gatt_write_cmd(GAttrib *attrib, uint16_t handle, uint8_t *value, int vlen,
 guint gatt_read_char_by_uuid(GAttrib *attrib, uint16_t start, uint16_t end,
 				bt_uuid_t *uuid, GAttribResultFunc func,
 				gpointer user_data);
+
+guint gatt_exchange_mtu(GAttrib *attrib, uint16_t mtu, GAttribResultFunc func,
+							gpointer user_data);
-- 
1.7.0.4

[PATCHv2 5/5] Add Exchange MTU in interactive gatttool

[Bruna Moreira]

---
 attrib/interactive.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 62 insertions(+), 0 deletions(-)

diff --git a/attrib/interactive.c b/attrib/interactive.c
index a9157e7..3fafb1e 100644
--- a/attrib/interactive.c
+++ b/attrib/interactive.c
@@ -362,6 +362,7 @@ static void cmd_disconnect(int argcp, char **argvp)
 
 	g_attrib_unref(attrib);
 	attrib = NULL;
+	opt_mtu = 0;
 
 	g_io_channel_shutdown(iochannel, FALSE, NULL);
 	g_io_channel_unref(iochannel);
@@ -654,6 +655,65 @@ static void cmd_sec_level(int argcp, char **argvp)
 	}
 }
 
+static void exchange_mtu_cb(guint8 status, const guint8 *pdu, guint16 plen,
+							gpointer user_data)
+{
+	uint16_t mtu;
+
+	if (status != 0) {
+		printf("Exchange MTU Request failed: %s\n",
+							att_ecode2str(status));
+		return;
+	}
+
+	if (!dec_mtu_resp(pdu, plen, &mtu)) {
+		printf("Protocol error\n");
+		return;
+	}
+
+	mtu = MIN(mtu, opt_mtu);
+	/* Set new value for MTU in client */
+	if (g_attrib_set_mtu(attrib, mtu))
+		printf("MTU was exchanged successfully: %d\n", mtu);
+	else
+		printf("Error exchanging MTU\n");
+}
+
+static void cmd_mtu(int argcp, char **argvp)
+{
+	if (conn_state != STATE_CONNECTED) {
+		printf("Command failed: not connected.\n");
+		return;
+	}
+
+	if (opt_psm) {
+		printf("Command failed: operation is only available for LE"
+							" transport.\n");
+		return;
+	}
+
+	if (argcp < 2) {
+		printf("Usage: mtu <value>\n");
+		return;
+	}
+
+	if (opt_mtu) {
+		printf("Command failed: MTU exchange can only occur once per"
+							" connection.\n");
+		return;
+	}
+
+	errno = 0;
+	opt_mtu = strtoll(argvp[1], NULL, 0);
+	if (errno != 0 || opt_mtu < ATT_DEFAULT_LE_MTU) {
+		printf("Invalid value. Minimum MTU size is %d\n",
+							ATT_DEFAULT_LE_MTU);
+		return;
+	}
+
+	gatt_exchange_mtu(attrib, opt_mtu, exchange_mtu_cb, NULL);
+}
+
 static struct {
 	const char *cmd;
 	void (*func)(int argcp, char **argvp);
@@ -684,6 +744,8 @@ static struct {
 		"Characteristic Value Write (No response)" },
 	{ "sec-level",		cmd_sec_level,	"[low | medium | high]",
 		"Set security level. Default: low" },
+	{ "mtu",		cmd_mtu,	"<value>",
+		"Exchange MTU for GATT/ATT" },
 	{ NULL, NULL, NULL}
 };
 
-- 
1.7.0.4