drbd: Receiving of delay_probes

Delay_probes are new packets in the DRBD protocol, which allow
DRBD to know the current delay packets have on the data socket.
(relative to the meta data socket)
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -209,8 +209,11 @@ enum drbd_packets {
 	P_RS_IS_IN_SYNC	      = 0x22, /* meta socket */
 	P_SYNC_PARAM89	      = 0x23, /* data socket, protocol version 89 replacement for P_SYNC_PARAM */
 	P_COMPRESSED_BITMAP   = 0x24, /* compressed or otherwise encoded bitmap transfer */
+	/* P_CKPT_FENCE_REQ      = 0x25, * currently reserved for protocol D */
+	/* P_CKPT_DISABLE_REQ    = 0x26, * currently reserved for protocol D */
+	P_DELAY_PROBE         = 0x27, /* is used on BOTH sockets */
 
-	P_MAX_CMD	      = 0x25,
+	P_MAX_CMD	      = 0x28,
 	P_MAY_IGNORE	      = 0x100, /* Flag to test if (cmd > P_MAY_IGNORE) ... */
 	P_MAX_OPT_CMD	      = 0x101,
 
@@ -540,6 +543,18 @@ struct p_compressed_bm {
 	u8 code[0];
 } __packed;
 
+struct p_delay_probe {
+	struct p_header head;
+	u32	seq_num; /* sequence number to match the two probe packets */
+	u32	offset;	 /* usecs the probe got sent after the reference time point */
+} __packed;
+
+struct delay_probe {
+	struct list_head list;
+	int seq_num;
+	struct timeval time;
+};
+
 /* DCBP: Drbd Compressed Bitmap Packet ... */
 static inline enum drbd_bitmap_code
 DCBP_get_code(struct p_compressed_bm *p)
@@ -1028,6 +1043,9 @@ struct drbd_conf {
 	u64 ed_uuid; /* UUID of the exposed data */
 	struct mutex state_mutex;
 	char congestion_reason;  /* Why we where congested... */
+	struct list_head delay_probes; /* protected by peer_seq_lock */
+	int data_delay;   /* Delay of packets on the data-sock behind meta-sock */
+	atomic_t delay_seq; /* To generate sequence numbers of delay probes */
 };
 
 static inline struct drbd_conf *minor_to_mdev(unsigned int minor)

drivers/block/drbd/drbd_main.c

@@ -2608,6 +2608,7 @@ void drbd_init_set_defaults(struct drbd_conf *mdev)
 	atomic_set(&mdev->net_cnt, 0);
 	atomic_set(&mdev->packet_seq, 0);
 	atomic_set(&mdev->pp_in_use, 0);
+	atomic_set(&mdev->delay_seq, 0);
 
 	mutex_init(&mdev->md_io_mutex);
 	mutex_init(&mdev->data.mutex);
@@ -2636,6 +2637,8 @@ void drbd_init_set_defaults(struct drbd_conf *mdev)
 	INIT_LIST_HEAD(&mdev->unplug_work.list);
 	INIT_LIST_HEAD(&mdev->md_sync_work.list);
 	INIT_LIST_HEAD(&mdev->bm_io_work.w.list);
+	INIT_LIST_HEAD(&mdev->delay_probes);
+
 	mdev->resync_work.cb  = w_resync_inactive;
 	mdev->unplug_work.cb  = w_send_write_hint;
 	mdev->md_sync_work.cb = w_md_sync;

drivers/block/drbd/drbd_receiver.c

@@ -3501,6 +3501,92 @@ static int receive_UnplugRemote(struct drbd_conf *mdev, struct p_header *h)
 	return TRUE;
 }
 
+static void timeval_sub_us(struct timeval* tv, unsigned int us)
+{
+	tv->tv_sec -= us / 1000000;
+	us = us % 1000000;
+	if (tv->tv_usec > us) {
+		tv->tv_usec += 1000000;
+		tv->tv_sec--;
+	}
+	tv->tv_usec -= us;
+}
+
+static void got_delay_probe(struct drbd_conf *mdev, int from, struct p_delay_probe *p)
+{
+	struct delay_probe *dp;
+	struct list_head *le;
+	struct timeval now;
+	int seq_num;
+	int offset;
+	int data_delay;
+
+	seq_num = be32_to_cpu(p->seq_num);
+	offset  = be32_to_cpu(p->offset);
+
+	spin_lock(&mdev->peer_seq_lock);
+	if (!list_empty(&mdev->delay_probes)) {
+		if (from == USE_DATA_SOCKET)
+			le = mdev->delay_probes.next;
+		else
+			le = mdev->delay_probes.prev;
+
+		dp = list_entry(le, struct delay_probe, list);
+
+		if (dp->seq_num == seq_num) {
+			list_del(le);
+			spin_unlock(&mdev->peer_seq_lock);
+			do_gettimeofday(&now);
+			timeval_sub_us(&now, offset);
+			data_delay =
+				now.tv_usec - dp->time.tv_usec +
+				(now.tv_sec - dp->time.tv_sec) * 1000000;
+
+			if (data_delay > 0)
+				mdev->data_delay = data_delay;
+
+			kfree(dp);
+			return;
+		}
+
+		if (dp->seq_num > seq_num) {
+			spin_unlock(&mdev->peer_seq_lock);
+			dev_warn(DEV, "Previous allocation failure of struct delay_probe?\n");
+			return; /* Do not alloca a struct delay_probe.... */
+		}
+	}
+	spin_unlock(&mdev->peer_seq_lock);
+
+	dp = kmalloc(sizeof(struct delay_probe), GFP_NOIO);
+	if (!dp) {
+		dev_warn(DEV, "Failed to allocate a struct delay_probe, do not worry.\n");
+		return;
+	}
+
+	dp->seq_num = seq_num;
+	do_gettimeofday(&dp->time);
+	timeval_sub_us(&dp->time, offset);
+
+	spin_lock(&mdev->peer_seq_lock);
+	if (from == USE_DATA_SOCKET)
+		list_add(&dp->list, &mdev->delay_probes);
+	else
+		list_add_tail(&dp->list, &mdev->delay_probes);
+	spin_unlock(&mdev->peer_seq_lock);
+}
+
+static int receive_delay_probe(struct drbd_conf *mdev, struct p_header *h)
+{
+	struct p_delay_probe *p = (struct p_delay_probe *)h;
+
+	ERR_IF(h->length != (sizeof(*p)-sizeof(*h))) return FALSE;
+	if (drbd_recv(mdev, h->payload, h->length) != h->length)
+		return FALSE;
+
+	got_delay_probe(mdev, USE_DATA_SOCKET, p);
+	return TRUE;
+}
+
 typedef int (*drbd_cmd_handler_f)(struct drbd_conf *, struct p_header *);
 
 static drbd_cmd_handler_f drbd_default_handler[] = {
@@ -3524,6 +3610,7 @@ static drbd_cmd_handler_f drbd_default_handler[] = {
 	[P_OV_REQUEST]      = receive_DataRequest,
 	[P_OV_REPLY]        = receive_DataRequest,
 	[P_CSUM_RS_REQUEST]    = receive_DataRequest,
+	[P_DELAY_PROBE]     = receive_delay_probe,
 	/* anything missing from this table is in
 	 * the asender_tbl, see get_asender_cmd */
 	[P_MAX_CMD]	    = NULL,
@@ -4300,6 +4387,14 @@ static int got_OVResult(struct drbd_conf *mdev, struct p_header *h)
 	return TRUE;
 }
 
+static int got_delay_probe_m(struct drbd_conf *mdev, struct p_header *h)
+{
+	struct p_delay_probe *p = (struct p_delay_probe *)h;
+
+	got_delay_probe(mdev, USE_META_SOCKET, p);
+	return TRUE;
+}
+
 struct asender_cmd {
 	size_t pkt_size;
 	int (*process)(struct drbd_conf *mdev, struct p_header *h);
@@ -4324,6 +4419,7 @@ static struct asender_cmd *get_asender_cmd(int cmd)
 	[P_BARRIER_ACK]	    = { sizeof(struct p_barrier_ack), got_BarrierAck },
 	[P_STATE_CHG_REPLY] = { sizeof(struct p_req_state_reply), got_RqSReply },
 	[P_RS_IS_IN_SYNC]   = { sizeof(struct p_block_ack), got_IsInSync },
+	[P_DELAY_PROBE]     = { sizeof(struct p_delay_probe), got_delay_probe_m },
 	[P_MAX_CMD]	    = { 0, NULL },
 	};
 	if (cmd > P_MAX_CMD || asender_tbl[cmd].process == NULL)