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Subject: Re: [PATCH 02/11] shared/gatt: Implement bt_gatt_exchange_mtu.
From: Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <1405718037-15401-3-git-send-email-armansito@chromium.org>
Date: Wed, 23 Jul 2014 01:25:41 +0200
Cc: linux-bluetooth@vger.kernel.org
Message-Id: <8A469641-D16A-4AF9-8557-AD5EE3B17571@holtmann.org>
References: <1405718037-15401-1-git-send-email-armansito@chromium.org> <1405718037-15401-3-git-send-email-armansito@chromium.org>
To: Arman Uguray <armansito@chromium.org>
Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Arman,

> This patch implements the helper function bt_gatt_exchange_mtu, which performs
> an ATT "Exchange MTU" request and resizes the internal buffer based on the
> result.
> ---
> src/shared/gatt-helpers.c | 87 +++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 85 insertions(+), 2 deletions(-)
> 
> diff --git a/src/shared/gatt-helpers.c b/src/shared/gatt-helpers.c
> index 3d85868..9cf05cf 100644
> --- a/src/shared/gatt-helpers.c
> +++ b/src/shared/gatt-helpers.c
> @@ -30,14 +30,97 @@
> #include "src/shared/att.h"
> #include "lib/uuid.h"
> #include "src/shared/gatt-helpers.h"
> +#include "src/shared/util.h"
> +
> +#ifndef MIN
> +#define MIN(a, b) ((a) < (b) ? (a) : (b))
> +#endif
> +
> +struct mtu_op {
> +	struct bt_att *att;
> +	uint16_t client_rx_mtu;
> +	bt_gatt_result_callback_t callback;
> +	void *user_data;
> +	bt_gatt_destroy_func_t destroy;
> +};
> +
> +static void destroy_mtu_op(void *user_data)
> +{
> +	struct mtu_op *op = user_data;
> +
> +	if (op->destroy)
> +		op->destroy(op->user_data);
> +
> +	free(op);
> +}
> +
> +static uint16_t process_error(const void *pdu, uint16_t length)
> +{
> +	if (!pdu || length != 4)
> +		return BT_GATT_ERROR_INVALID_RSP;
> +
> +	return (uint16_t)((uint8_t *) pdu)[3];
> +}

I am not convinced by the uint16 status, but in case you do these things, create a uint16_t local variable and assign the uint8_t value to it and then return.  It is a clearer, then the double casting.

> +
> +static void mtu_cb(uint8_t opcode, const void *pdu, uint16_t length,
> +								void *user_data)
> +{
> +	struct mtu_op *op = user_data;
> +	uint16_t result = 0;
> +	uint16_t server_rx_mtu;
> +
> +	if (opcode == BT_ATT_OP_ERROR_RSP) {
> +		result = process_error(pdu, length);
> +		goto done;
> +	}
> +
> +	if (opcode != BT_ATT_OP_MTU_RSP || !pdu || length != 2) {
> +		result = BT_GATT_ERROR_INVALID_RSP;
> +		goto done;
> +	}
> +
> +	server_rx_mtu = get_le16(pdu);
> +	bt_att_set_mtu(op->att, MIN(op->client_rx_mtu, server_rx_mtu));
> +
> +done:
> +	if (op->callback)
> +		op->callback(result, op->user_data);
> +}
> 
> bool bt_gatt_exchange_mtu(struct bt_att *att, uint16_t client_rx_mtu,
> 					bt_gatt_result_callback_t callback,
> 					void *user_data,
> 					bt_gatt_destroy_func_t destroy)
> {
> -	/* TODO */
> -	return false;
> +	struct mtu_op *op;
> +	uint8_t pdu[2];
> +
> +	if (!att)
> +		return false;
> +
> +	if (!client_rx_mtu)
> +		return false;
> +
> +	op = new0(struct mtu_op, 1);
> +	if (!op)
> +		return false;
> +
> +	op->att = att;
> +	op->client_rx_mtu = client_rx_mtu;
> +	op->callback = callback;
> +	op->user_data = user_data;
> +	op->destroy = destroy;
> +
> +	put_le16(client_rx_mtu, pdu);
> +
> +	if (!bt_att_send(att, BT_ATT_OP_MTU_REQ, pdu, sizeof(pdu),
> +							mtu_cb, op,
> +							destroy_mtu_op)) {
> +		free(op);
> +		return false;
> +	}
> +
> +	return true;
> }

Regards

Marcel