Re: [PATCHv2 1/2] Bluetooth: Add the l2cap_seq_list structure for tracking frames

[Marcel Holtmann <marcel@holtmann.org>]

Hi Mat,

> A sequence list is a data structure used to track frames that need to
> be retransmitted, and frames that have been requested for
> retransmission by the remote device.  It can compactly represent a
> list of sequence numbers within the ERTM transmit window.  Memory for
> the list is allocated once at connection time, and common operations
> in ERTM are O(1).
> 
> Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
> ---
>  include/net/bluetooth/l2cap.h |   12 ++++
>  net/bluetooth/l2cap_core.c    |  132 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 144 insertions(+)
> 
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index f6f0500..5d65b3d 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -407,6 +407,16 @@ struct l2cap_conn_param_update_rsp {
>  #define L2CAP_CONN_PARAM_REJECTED	0x0001
>  
>  /* ----- L2CAP channels and connections ----- */
> +struct l2cap_seq_list {
> +	__u16	head;
> +	__u16	tail;
> +	__u16	mask;
> +	__u16	*list;
> +};
> +
> +#define L2CAP_SEQ_LIST_CLEAR	0xFFFF
> +#define L2CAP_SEQ_LIST_TAIL	0x8000
> +
>  struct srej_list {
>  	__u16	tx_seq;
>  	struct list_head list;
> @@ -501,6 +511,8 @@ struct l2cap_chan {
>  	struct sk_buff		*tx_send_head;
>  	struct sk_buff_head	tx_q;
>  	struct sk_buff_head	srej_q;
> +	struct l2cap_seq_list	srej_list;
> +	struct l2cap_seq_list	retrans_list;
>  	struct list_head	srej_l;
>  
>  	struct list_head	list;
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 3caff27..2414ddd 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -233,6 +233,134 @@ static inline void l2cap_chan_set_err(struct l2cap_chan *chan, int err)
>  	release_sock(sk);
>  }
>  
> +/* ---- L2CAP sequence number lists ---- */
> +
> +/* For ERTM, ordered lists of sequence numbers must be tracked for
> + * SREJ requests that are received and for frames that are to be
> + * retransmitted. These seq_list functions implement a singly-linked
> + * list in an array, where membership in the list can also be checked
> + * in constant time. Items can also be added to the tail of the list
> + * and removed from the head in constant time, without further memory
> + * allocs or frees.
> + */
> +
> +static int l2cap_seq_list_init(struct l2cap_seq_list *seq_list, u16 size)
> +{
> +	u16 alloc_size = 1;
> +	int err = 0;
> +	int i;
> +
> +	/* Allocated size is a power of 2 to map sequence numbers
> +	 * (which may be up to 14 bits) in to a smaller array that is
> +	 * sized for the negotiated ERTM transmit windows.
> +	 */
> +	while (alloc_size && alloc_size <= size)
> +		alloc_size <<= 1;
> +	if (!alloc_size)
> +		return -ENOMEM;
> +
> +	seq_list->list = kzalloc(sizeof(u16) * alloc_size, GFP_KERNEL);
> +	if (!seq_list->list)
> +		return -ENOMEM;
> +
> +	seq_list->mask = alloc_size - 1;
> +	seq_list->head = L2CAP_SEQ_LIST_CLEAR;
> +	seq_list->tail = L2CAP_SEQ_LIST_CLEAR;
> +	for (i = 0; i < alloc_size; i++)
> +		seq_list->list[i] = L2CAP_SEQ_LIST_CLEAR;
> +
> +	return err;
> +}
> +
> +static inline void l2cap_seq_list_free(struct l2cap_seq_list *seq_list)
> +{
> +	kfree(seq_list->list);
> +}
> +
> +static inline bool l2cap_seq_list_contains(struct l2cap_seq_list *seq_list,
> +					   u16 seq)
> +{
> +	/* Constant-time check for list membership */
> +	return seq_list->list[seq & seq_list->mask] != L2CAP_SEQ_LIST_CLEAR;
> +}
> +
> +static u16 l2cap_seq_list_remove(struct l2cap_seq_list *seq_list, u16 seq)
> +{
> +	u16 mask = seq_list->mask;
> +
> +	BT_DBG("seq_list %p, seq %d", seq_list, (int) seq);
> +
> +	if (seq_list->head == L2CAP_SEQ_LIST_CLEAR) {
> +		/* In case someone tries to pop the head of an empty list */
> +		BT_DBG("List empty");

I think that see debug statement should go away. Do you really need
them?

> +		return L2CAP_SEQ_LIST_CLEAR;
> +	} else if (seq_list->head == seq) {
> +		/* Head can be removed in constant time */
> +		BT_DBG("Remove head");
> +		seq_list->head = seq_list->list[seq & mask];
> +		seq_list->list[seq & mask] = L2CAP_SEQ_LIST_CLEAR;
> +
> +		if (seq_list->head == L2CAP_SEQ_LIST_TAIL) {
> +			seq_list->head = L2CAP_SEQ_LIST_CLEAR;
> +			seq_list->tail = L2CAP_SEQ_LIST_CLEAR;
> +		}
> +	} else {
> +		/* Walk the list to find the sequence number */
> +		u16 prev = seq_list->head;
> +		BT_DBG("Find and remove");
> +		while (seq_list->list[prev & mask] != seq) {
> +			prev = seq_list->list[prev & mask];
> +			if (prev == L2CAP_SEQ_LIST_TAIL) {
> +				BT_DBG("seq %d not in list", (int) seq);
> +				return L2CAP_SEQ_LIST_CLEAR;
> +			}
> +		}
> +
> +		/* Unlink the number from the list and clear it */
> +		seq_list->list[prev & mask] = seq_list->list[seq & mask];
> +		seq_list->list[seq & mask] = L2CAP_SEQ_LIST_CLEAR;
> +		if (seq_list->tail == seq)
> +			seq_list->tail = prev;
> +	}
> +	return seq;
> +}
> +
> +static u16 l2cap_seq_list_pop(struct l2cap_seq_list *seq_list)
> +{
> +	/* Remove the head in constant time */
> +	return l2cap_seq_list_remove(seq_list, seq_list->head);
> +}
> +
> +static void l2cap_seq_list_clear(struct l2cap_seq_list *seq_list)
> +{
> +	if (seq_list->head != L2CAP_SEQ_LIST_CLEAR) {
> +		u16 i;
> +		for (i = 0; i <= seq_list->mask; i++)
> +			seq_list->list[i] = L2CAP_SEQ_LIST_CLEAR;
> +
> +		seq_list->head = L2CAP_SEQ_LIST_CLEAR;
> +		seq_list->tail = L2CAP_SEQ_LIST_CLEAR;
> +	}
> +}
> +
> +static void l2cap_seq_list_append(struct l2cap_seq_list *seq_list, u16 seq)
> +{
> +	u16 mask = seq_list->mask;
> +
> +	/* All appends happen in constant time */
> +	BT_DBG("seq_list %p, seq %d", seq_list, (int) seq);
> +
> +	if (seq_list->list[seq & mask] == L2CAP_SEQ_LIST_CLEAR) {
> +		if (seq_list->tail == L2CAP_SEQ_LIST_CLEAR)
> +			seq_list->head = seq;
> +		else
> +			seq_list->list[seq_list->tail & mask] = seq;
> +
> +		seq_list->tail = seq;
> +		seq_list->list[seq & mask] = L2CAP_SEQ_LIST_TAIL;
> +	}
> +}
> +
>  static void l2cap_chan_timeout(struct work_struct *work)
>  {
>  	struct l2cap_chan *chan = container_of(work, struct l2cap_chan,
> @@ -404,6 +532,8 @@ static void l2cap_chan_del(struct l2cap_chan *chan, int err)
>  
>  		skb_queue_purge(&chan->srej_q);
>  
> +		l2cap_seq_list_free(&chan->srej_list);
> +		l2cap_seq_list_free(&chan->retrans_list);
>  		list_for_each_entry_safe(l, tmp, &chan->srej_l, list) {
>  			list_del(&l->list);
>  			kfree(l);
> @@ -2052,6 +2182,8 @@ static inline void l2cap_ertm_init(struct l2cap_chan *chan)
>  
>  	skb_queue_head_init(&chan->srej_q);
>  
> +	l2cap_seq_list_init(&chan->srej_list, chan->tx_win);
> +	l2cap_seq_list_init(&chan->retrans_list, chan->remote_tx_win);
>  	INIT_LIST_HEAD(&chan->srej_l);
>  }
>  

Besides removing the debug statements, this looks good to me.

Acked-by: Marcel Holtmann <marcel@holtmann.org>

Regards

Marcel