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Bluetooth: Add the l2cap_seq_list structure for tracking frames
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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>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
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Mat Martineau authored and Gustavo Padovan committed May 9, 2012
1 parent 9033894 commit 3c58819
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Showing 2 changed files with 154 additions and 8 deletions.
12 changes: 12 additions & 0 deletions include/net/bluetooth/l2cap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down
150 changes: 142 additions & 8 deletions net/bluetooth/l2cap_core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -232,6 +232,121 @@ 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)
{
size_t alloc_size, 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.
*/
alloc_size = roundup_pow_of_two(size);

seq_list->list = kmalloc(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 0;
}

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;

if (seq_list->head == L2CAP_SEQ_LIST_CLEAR) {
/* In case someone tries to pop the head of an empty list */
return L2CAP_SEQ_LIST_CLEAR;
} else if (seq_list->head == seq) {
/* Head can be removed in constant time */
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;
while (seq_list->list[prev & mask] != seq) {
prev = seq_list->list[prev & mask];
if (prev == L2CAP_SEQ_LIST_TAIL)
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 inline 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 */

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,
Expand Down Expand Up @@ -414,6 +529,8 @@ 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);
Expand Down Expand Up @@ -2045,8 +2162,10 @@ static void l2cap_ack_timeout(struct work_struct *work)
l2cap_chan_put(chan);
}

static inline void l2cap_ertm_init(struct l2cap_chan *chan)
static inline int l2cap_ertm_init(struct l2cap_chan *chan)
{
int err;

chan->expected_ack_seq = 0;
chan->unacked_frames = 0;
chan->buffer_seq = 0;
Expand All @@ -2060,6 +2179,11 @@ static inline void l2cap_ertm_init(struct l2cap_chan *chan)
skb_queue_head_init(&chan->srej_q);

INIT_LIST_HEAD(&chan->srej_l);
err = l2cap_seq_list_init(&chan->srej_list, chan->tx_win);
if (err < 0)
return err;

return l2cap_seq_list_init(&chan->retrans_list, chan->remote_tx_win);
}

static inline __u8 l2cap_select_mode(__u8 mode, __u16 remote_feat_mask)
Expand Down Expand Up @@ -2853,7 +2977,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr
u16 dcid, flags;
u8 rsp[64];
struct l2cap_chan *chan;
int len;
int len, err = 0;

dcid = __le16_to_cpu(req->dcid);
flags = __le16_to_cpu(req->flags);
Expand Down Expand Up @@ -2924,9 +3048,13 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr
chan->expected_tx_seq = 0;
skb_queue_head_init(&chan->tx_q);
if (chan->mode == L2CAP_MODE_ERTM)
l2cap_ertm_init(chan);
err = l2cap_ertm_init(chan);

if (err < 0)
l2cap_send_disconn_req(chan->conn, chan, -err);
else
l2cap_chan_ready(chan);

l2cap_chan_ready(chan);
goto unlock;
}

Expand Down Expand Up @@ -2954,7 +3082,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr

unlock:
l2cap_chan_unlock(chan);
return 0;
return err;
}

static inline int l2cap_config_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd, u8 *data)
Expand All @@ -2963,6 +3091,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hdr
u16 scid, flags, result;
struct l2cap_chan *chan;
int len = le16_to_cpu(cmd->len) - sizeof(*rsp);
int err = 0;

scid = __le16_to_cpu(rsp->scid);
flags = __le16_to_cpu(rsp->flags);
Expand Down Expand Up @@ -3054,14 +3183,17 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hdr
chan->expected_tx_seq = 0;
skb_queue_head_init(&chan->tx_q);
if (chan->mode == L2CAP_MODE_ERTM)
l2cap_ertm_init(chan);
err = l2cap_ertm_init(chan);

l2cap_chan_ready(chan);
if (err < 0)
l2cap_send_disconn_req(chan->conn, chan, -err);
else
l2cap_chan_ready(chan);
}

done:
l2cap_chan_unlock(chan);
return 0;
return err;
}

static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd, u8 *data)
Expand Down Expand Up @@ -3805,6 +3937,7 @@ static void l2cap_ertm_enter_local_busy(struct l2cap_chan *chan)
BT_DBG("chan %p, Enter local busy", chan);

set_bit(CONN_LOCAL_BUSY, &chan->conn_state);
l2cap_seq_list_clear(&chan->srej_list);

__set_ack_timer(chan);
}
Expand Down Expand Up @@ -3897,6 +4030,7 @@ static int l2cap_send_srejframe(struct l2cap_chan *chan, u16 tx_seq)
while (tx_seq != chan->expected_tx_seq) {
control = __set_ctrl_super(chan, L2CAP_SUPER_SREJ);
control |= __set_reqseq(chan, chan->expected_tx_seq);
l2cap_seq_list_append(&chan->srej_list, chan->expected_tx_seq);
l2cap_send_sframe(chan, control);

new = kzalloc(sizeof(struct srej_list), GFP_ATOMIC);
Expand Down

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