Bluetooth: Enable option to configure Max Transmission value via sockopt

With the sockopt extension we can set a per-channel MaxTx value.
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/l2cap.h

@@ -55,6 +55,7 @@ struct l2cap_options {
 	__u16 flush_to;
 	__u8  mode;
 	__u8  fcs;
+	__u8  max_tx;
 	__u16 txwin_size;
 };
 
@@ -340,6 +341,7 @@ struct l2cap_pinfo {
 	__u8		ident;
 
 	__u8		tx_win;
+	__u8		max_tx;
 	__u8		remote_tx_win;
 	__u8		remote_max_tx;
 	__u16		retrans_timeout;

net/bluetooth/l2cap.c

@@ -783,6 +783,7 @@ static void l2cap_sock_init(struct sock *sk, struct sock *parent)
 		pi->omtu = l2cap_pi(parent)->omtu;
 		pi->mode = l2cap_pi(parent)->mode;
 		pi->fcs  = l2cap_pi(parent)->fcs;
+		pi->max_tx = l2cap_pi(parent)->max_tx;
 		pi->tx_win = l2cap_pi(parent)->tx_win;
 		pi->sec_level = l2cap_pi(parent)->sec_level;
 		pi->role_switch = l2cap_pi(parent)->role_switch;
@@ -791,6 +792,7 @@ static void l2cap_sock_init(struct sock *sk, struct sock *parent)
 		pi->imtu = L2CAP_DEFAULT_MTU;
 		pi->omtu = 0;
 		pi->mode = L2CAP_MODE_BASIC;
+		pi->max_tx = max_transmit;
 		pi->fcs  = L2CAP_FCS_CRC16;
 		pi->tx_win = tx_window;
 		pi->sec_level = BT_SECURITY_LOW;
@@ -1785,6 +1787,7 @@ static int l2cap_sock_setsockopt_old(struct socket *sock, int optname, char __us
 		opts.flush_to = l2cap_pi(sk)->flush_to;
 		opts.mode     = l2cap_pi(sk)->mode;
 		opts.fcs      = l2cap_pi(sk)->fcs;
+		opts.max_tx   = l2cap_pi(sk)->max_tx;
 		opts.txwin_size = (__u16)l2cap_pi(sk)->tx_win;
 
 		len = min_t(unsigned int, sizeof(opts), optlen);
@@ -1797,6 +1800,7 @@ static int l2cap_sock_setsockopt_old(struct socket *sock, int optname, char __us
 		l2cap_pi(sk)->omtu = opts.omtu;
 		l2cap_pi(sk)->mode = opts.mode;
 		l2cap_pi(sk)->fcs  = opts.fcs;
+		l2cap_pi(sk)->max_tx = opts.max_tx;
 		l2cap_pi(sk)->tx_win = (__u8)opts.txwin_size;
 		break;
 
@@ -1912,6 +1916,7 @@ static int l2cap_sock_getsockopt_old(struct socket *sock, int optname, char __us
 		opts.flush_to = l2cap_pi(sk)->flush_to;
 		opts.mode     = l2cap_pi(sk)->mode;
 		opts.fcs      = l2cap_pi(sk)->fcs;
+		opts.max_tx   = l2cap_pi(sk)->max_tx;
 		opts.txwin_size = (__u16)l2cap_pi(sk)->tx_win;
 
 		len = min_t(unsigned int, len, sizeof(opts));
@@ -2331,7 +2336,7 @@ static int l2cap_build_conf_req(struct sock *sk, void *data)
 	case L2CAP_MODE_ERTM:
 		rfc.mode            = L2CAP_MODE_ERTM;
 		rfc.txwin_size      = pi->tx_win;
-		rfc.max_transmit    = max_transmit;
+		rfc.max_transmit    = pi->max_tx;
 		rfc.retrans_timeout = 0;
 		rfc.monitor_timeout = 0;
 		rfc.max_pdu_size    = cpu_to_le16(L2CAP_DEFAULT_MAX_PDU_SIZE);