Bluetooth: Add the l2cap_seq_list structure for tracking frames

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>

1 files changed, 142 insertions, 8 deletions

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 03746f565fc..041ebed9e64 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -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,
@@ -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);
@@ -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;
@@ -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)
@@ -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);
@@ -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;
         }
 
@@ -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)
@@ -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);
@@ -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)
@@ -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);
 }
@@ -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);