RFC: Allow Bluez to select flushable or non-flushable ACL packets with L2CAP_LM_RELIABLE

[Nick Pelly <npelly@google.com>]

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Right now Bluez always requests flushable ACL packets (but does not
set a flush timeout, so effectively they are non-flushable):

However it is desirable to use an ACL flush timeout on A2DP packets so
that if the ACL packets block for some reason then the LM can flush
them to make room for newer packets.

Is it reasonable for Bluez to use the 0x00 ACL packet boundary flag by
default (non-flushable packet), and let userspace request flushable
packets on A2DP L2CAP sockets with the socket option
L2CAP_LM_RELIABLE.

Make sense? Any other suggestions?

Attached is a rough (untested) patch of what I had in mind.

See core spec 2.E.5.4.2 for reference.

Nick

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From 90f997071d3e795d6e674821c1d0f4057edb5838 Mon Sep 17 00:00:00 2001
From: Nick Pelly <npelly@google.com>
Date: Tue, 8 Dec 2009 19:42:21 -0800
Subject: [PATCH] Bluetooth: Send non-flushable ACL packets by default.

L2CAP sockets can request flushable ACL packets with L2CAP_LM_RELIABLE

Signed-off-by: Nick Pelly <npelly@google.com>
---
 include/net/bluetooth/hci.h |    3 +++
 net/bluetooth/hci_core.c    |    6 ++++--
 net/bluetooth/l2cap.c       |   10 ++++++++--
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index f69f015..c6f6ce5 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -142,11 +142,14 @@ enum {
 #define EDR_ESCO_MASK  (ESCO_2EV3 | ESCO_3EV3 | ESCO_2EV5 | ESCO_3EV5)
 
 /* ACL flags */
+#define ACL_START_FLUSHABLE	0x00
 #define ACL_CONT		0x01
 #define ACL_START		0x02
 #define ACL_ACTIVE_BCAST	0x04
 #define ACL_PICO_BCAST		0x08
 
+#define ACL_PB_MASK	(ACL_CONT | ACL_START)
+
 /* Baseband links */
 #define SCO_LINK	0x00
 #define ACL_LINK	0x01
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index cd06151..aeaf07f 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1200,7 +1200,7 @@ int hci_send_acl(struct hci_conn *conn, struct sk_buff *skb, __u16 flags)
 
 	skb->dev = (void *) hdev;
 	bt_cb(skb)->pkt_type = HCI_ACLDATA_PKT;
-	hci_add_acl_hdr(skb, conn->handle, flags | ACL_START);
+	hci_add_acl_hdr(skb, conn->handle, flags);
 
 	if (!(list = skb_shinfo(skb)->frag_list)) {
 		/* Non fragmented */
@@ -1217,12 +1217,14 @@ int hci_send_acl(struct hci_conn *conn, struct sk_buff *skb, __u16 flags)
 		spin_lock_bh(&conn->data_q.lock);
 
 		__skb_queue_tail(&conn->data_q, skb);
+		flags &= ~ACL_PB_MASK;
+		flags |= ACL_CONT;
 		do {
 			skb = list; list = list->next;
 
 			skb->dev = (void *) hdev;
 			bt_cb(skb)->pkt_type = HCI_ACLDATA_PKT;
-			hci_add_acl_hdr(skb, conn->handle, flags | ACL_CONT);
+			hci_add_acl_hdr(skb, conn->handle, flags);
 
 			BT_DBG("%s frag %p len %d", hdev->name, skb, skb->len);
 
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index ca4d3b4..bf16a6a 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -325,7 +325,7 @@ static inline int l2cap_send_cmd(struct l2cap_conn *conn, u8 ident, u8 code, u16
 	if (!skb)
 		return -ENOMEM;
 
-	return hci_send_acl(conn->hcon, skb, 0);
+	return hci_send_acl(conn->hcon, skb, ACL_START);
 }
 
 static void l2cap_do_start(struct sock *sk)
@@ -1116,6 +1116,7 @@ static inline int l2cap_do_send(struct sock *sk, struct msghdr *msg, int len)
 	struct sk_buff *skb, **frag;
 	int err, hlen, count, sent=0;
 	struct l2cap_hdr *lh;
+	u16 flags;
 
 	BT_DBG("sk %p len %d", sk, len);
 
@@ -1168,7 +1169,12 @@ static inline int l2cap_do_send(struct sock *sk, struct msghdr *msg, int len)
 		frag = &(*frag)->next;
 	}
 
-	if ((err = hci_send_acl(conn->hcon, skb, 0)) < 0)
+	if (l2cap_pi(sk)->force_reliable)
+		flags = ACL_START;
+	else
+		flags = ACL_START_FLUSHABLE;
+
+	if ((err = hci_send_acl(conn->hcon, skb, flags)) < 0)
 		goto fail;
 
 	return sent;
-- 
1.6.5.3