On Wed, 11 Aug 2010, Gustavo F. Padovan wrote:
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.
That's what the code does, without violating the HCI MTU.
+ 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.
If there was room in the HCI fragment, count+2 bytes were allocated
with bt_skb_send_alloc. However, only count bytes were used by
skb_put.
This final block of code is doing two things:
1. Allocating a final HCI fragment for the FCS if there was not room
for the FCS in the last data fragment.
2. Doing the skb_put for the FCS bytes.
I will add some comments to this code to help clarify what's going on.
--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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