Re: [PATCH v3] Bluetooth: automatically flushable packets aren't allowed on LE links

Johan Hedberg
2014-11-20T11:38:25Z

Hi Steven,

On Wed, Nov 19, 2014, Steven Walter wrote:
> The bluetooth spec states that automatically flushable packets may not
> be sent over a LE-U link.
>
> Signed-off-by: Steven Walter <stevenrwalter@gmail.com>
> ---
> net/bluetooth/l2cap_core.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 4af3821..7c4350f 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -764,7 +764,7 @@ static void l2cap_send_cmd(struct l2cap_conn *conn, u8 ident, u8 code, u16 len,
> if (!skb)
> return;
>
> - if (lmp_no_flush_capable(conn->hcon->hdev))
> + if (lmp_no_flush_capable(conn->hcon->hdev) || conn->hcon->type == LE_LINK)
> flags = ACL_START_NO_FLUSH;
> else
> flags = ACL_START;
> @@ -784,7 +784,7 @@ static bool __chan_is_moving(struct l2cap_chan *chan)
> static void l2cap_do_send(struct l2cap_chan *chan, struct sk_buff *skb)
> {
> struct hci_conn *hcon = chan->conn->hcon;
> - u16 flags;
> + u16 flags = ACL_START;
>
> BT_DBG("chan %p, skb %p len %d priority %u", chan, skb, skb->len,
> skb->priority);
> @@ -798,11 +798,13 @@ static void l2cap_do_send(struct l2cap_chan *chan, struct sk_buff *skb)
> return;
> }
>
> - if (!test_bit(FLAG_FLUSHABLE, &chan->flags) &&
> - lmp_no_flush_capable(hcon->hdev))
> + if (hcon->type == LE_LINK) {
> + /* LE-U does not support auto-flushing packets */
> flags = ACL_START_NO_FLUSH;
> - else
> - flags = ACL_START;
> + } else if (!test_bit(FLAG_FLUSHABLE, &chan->flags) &&
> + lmp_no_flush_capable(hcon->hdev)) {
> + flags = ACL_START_NO_FLUSH;
> + }

I think Marcel was after just providing a clarifying code comment in
both places - having two branches of an if-statement doing exactly the
same thing looks a bit weird to me. To make thins completely clear I'd
suggest adding a simple helper function that you can call from both
places to get the needed flags, something like the following:

static u16 get_acl_flags(struct hci_conn *hcon, struct l2cap_chan *chan)
{
/* LE-U does not support auto-flushing packets */
if (hcon->type == LE_LINK)
return ACL_START_NO_FLUSH;

/* If non-flushable packets are not supported don't request them */
if (!lmp_no_flush_capable(hcon->hdev))
return ACL_START;

/* If the chan has requested auto-flushing go with that */
if (chan && test_bit(FLAG_FLUSHABLE, &chan->flags))
return ACL_START;

/* Otherwise go with a non-flushable packet */
return ACL_START_NO_FLUSH;
}

This way we'd avoid complex if-statements and can clearly document each
condition independently.

Johan