Hi Mat,
* Gustavo F. Padovan <gustavo@xxxxxxxxxxx> [2010-08-11 00:35:41 -0300]:
> * Mat Martineau <mathewm@xxxxxxxxxxxxxx> [2010-08-10 12:15:00 -0700]:
>
> > In order to not limit ERTM and streaming mode PDUs to the HCI MTU
> > size, L2CAP must be able to split PDUs in to multple HCI fragments.
> > This is done by allocating space for the FCS in the last fragment.
> >
> > Signed-off-by: Mat Martineau <mathewm@xxxxxxxxxxxxxx>
> > ---
> > net/bluetooth/l2cap.c | 39 ++++++++++++++++++++++++++++++++++-----
> > 1 files changed, 34 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> > index aa69c84..b485c4a 100644
> > --- a/net/bluetooth/l2cap.c
> > +++ b/net/bluetooth/l2cap.c
> > @@ -1664,31 +1664,63 @@ static inline int l2cap_skbuff_fromiovec(struct sock *sk, struct msghdr *msg, in
> > {
> > struct l2cap_conn *conn = l2cap_pi(sk)->conn;
> > struct sk_buff **frag;
> > + struct sk_buff *final;
> > int err, sent = 0;
> >
> > + BT_DBG("sk %p, msg %p, len %d, count %d, skb %p", sk,
> > + msg, (int)len, (int)count, skb);
> > +
> > if (memcpy_fromiovec(skb_put(skb, count), msg->msg_iov, count))
> > return -EFAULT;
> >
> > sent += count;
> > len -= count;
> > + final = skb;
> >
> > /* Continuation fragments (no L2CAP header) */
> > frag = &skb_shinfo(skb)->frag_list;
> > while (len) {
> > + int skblen;
> > count = min_t(unsigned int, conn->mtu, len);
> >
> > - *frag = bt_skb_send_alloc(sk, count, msg->msg_flags & MSG_DONTWAIT, &err);
> > + /* Add room for the FCS if it fits */
> > + if (l2cap_pi(sk)->fcs == L2CAP_FCS_CRC16 &&
> > + len + L2CAP_FCS_SIZE <= conn->mtu)
>
> You don't need to check for (len + L2CAP_FCS_SIZE <= conn=mtu) here.
> Section 5.1 point that:
>
> "Unlike the B-Frame length field, the I-frame length field may be greater
> than the configured MTU because it includes the octet lengths of the
> Control, L2CAP SDU Length (when present), and frame check sequence
> fields as well as the Information octets."
>
> From that I understand "len <=" and not "len + L2CAP_FCS_SIZE <="
So here you might want to the check if we support FCS, and then add 2 to
skblen.
>
>
> > + skblen = count + L2CAP_FCS_SIZE;
> > + else
> > + skblen = count;
> > +
> > + *frag = bt_skb_send_alloc(sk, skblen,
> > + msg->msg_flags & MSG_DONTWAIT, &err);
> > if (!*frag)
> > return -EFAULT;
> > - if (memcpy_fromiovec(skb_put(*frag, count), msg->msg_iov, count))
> > +
> > + if (memcpy_fromiovec(skb_put(*frag, count),
> > + msg->msg_iov, count))
> > return -EFAULT;
> >
> > sent += count;
> > len -= count;
> >
> > + final = *frag;
> > +
> > frag = &(*frag)->next;
> > }
> >
> > + if (l2cap_pi(sk)->fcs == L2CAP_FCS_CRC16) {
> > + if (skb_tailroom(final) < L2CAP_FCS_SIZE) {
> > + *frag = bt_skb_send_alloc(sk, L2CAP_FCS_SIZE,
> > + msg->msg_flags & MSG_DONTWAIT,
> > + &err);
Why do we need to check for FCS again? We already added it required
space to the last fragment.
--
Gustavo F. Padovan
http://padovan.org
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