libceph: implement RECONNECT_SEQ feature

This is an old protocol extension that allows the client and server to
avoid resending old messages after a reconnect (following a socket error).
Instead, the exchange their sequence numbers during the handshake.  This
avoids sending a bunch of useless data over the socket.

It has been supported in the server code since v0.22 (Sep 2010).

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>

3 files changed, 41 insertions, 5 deletions

diff --git a/include/linux/ceph/ceph_features.h b/include/linux/ceph/ceph_features.h
index 76554cecaab2..4c42080347af 100644
--- a/include/linux/ceph/ceph_features.h
+++ b/include/linux/ceph/ceph_features.h
@@ -41,6 +41,7 @@
  */
 #define CEPH_FEATURES_SUPPORTED_DEFAULT  \
         (CEPH_FEATURE_NOSRCADDR |               \
+         CEPH_FEATURE_RECONNECT_SEQ |           \
          CEPH_FEATURE_PGID64 |                  \
          CEPH_FEATURE_PGPOOL3 |                 \
          CEPH_FEATURE_OSDENC |                  \
@@ -51,6 +52,7 @@
 
 #define CEPH_FEATURES_REQUIRED_DEFAULT   \
         (CEPH_FEATURE_NOSRCADDR |        \
+         CEPH_FEATURE_RECONNECT_SEQ |    \
          CEPH_FEATURE_PGID64 |           \
          CEPH_FEATURE_PGPOOL3 |          \
          CEPH_FEATURE_OSDENC)
diff --git a/include/linux/ceph/msgr.h b/include/linux/ceph/msgr.h
index 680d3d648cac..3d94a73b5f30 100644
--- a/include/linux/ceph/msgr.h
+++ b/include/linux/ceph/msgr.h
@@ -87,6 +87,7 @@ struct ceph_entity_inst {
 #define CEPH_MSGR_TAG_BADPROTOVER  10  /* bad protocol version */
 #define CEPH_MSGR_TAG_BADAUTHORIZER 11 /* bad authorizer */
 #define CEPH_MSGR_TAG_FEATURES      12 /* insufficient features */
+#define CEPH_MSGR_TAG_SEQ           13 /* 64-bit int follows with seen seq number */
 
 
 /*
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 997daccf973a..e8491db43f5e 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -1247,6 +1247,24 @@ static void prepare_write_ack(struct ceph_connection *con)
 }
 
 /*
+ * Prepare to share the seq during handshake
+ */
+static void prepare_write_seq(struct ceph_connection *con)
+{
+        dout("prepare_write_seq %p %llu -> %llu\n", con,
+             con->in_seq_acked, con->in_seq);
+        con->in_seq_acked = con->in_seq;
+
+        con_out_kvec_reset(con);
+
+        con->out_temp_ack = cpu_to_le64(con->in_seq_acked);
+        con_out_kvec_add(con, sizeof (con->out_temp_ack),
+                         &con->out_temp_ack);
+
+        con_flag_set(con, CON_FLAG_WRITE_PENDING);
+}
+
+/*
  * Prepare to write keepalive byte.
  */
 static void prepare_write_keepalive(struct ceph_connection *con)
@@ -1582,6 +1600,13 @@ static void prepare_read_ack(struct ceph_connection *con)
         con->in_base_pos = 0;
 }
 
+static void prepare_read_seq(struct ceph_connection *con)
+{
+        dout("prepare_read_seq %p\n", con);
+        con->in_base_pos = 0;
+        con->in_tag = CEPH_MSGR_TAG_SEQ;
+}
+
 static void prepare_read_tag(struct ceph_connection *con)
 {
         dout("prepare_read_tag %p\n", con);
@@ -2059,6 +2084,7 @@ static int process_connect(struct ceph_connection *con)
                 prepare_read_connect(con);
                 break;
 
+        case CEPH_MSGR_TAG_SEQ:
         case CEPH_MSGR_TAG_READY:
                 if (req_feat & ~server_feat) {
                         pr_err("%s%lld %s protocol feature mismatch,"
@@ -2089,7 +2115,12 @@ static int process_connect(struct ceph_connection *con)
 
                 con->delay = 0;      /* reset backoff memory */
 
-                prepare_read_tag(con);
+                if (con->in_reply.tag == CEPH_MSGR_TAG_SEQ) {
+                        prepare_write_seq(con);
+                        prepare_read_seq(con);
+                } else {
+                        prepare_read_tag(con);
+                }
                 break;
 
         case CEPH_MSGR_TAG_WAIT:
@@ -2123,7 +2154,6 @@ static int read_partial_ack(struct ceph_connection *con)
         return read_partial(con, end, size, &con->in_temp_ack);
 }
 
-
 /*
  * We can finally discard anything that's been acked.
  */
@@ -2148,8 +2178,6 @@ static void process_ack(struct ceph_connection *con)
 }
 
 
-
-
 static int read_partial_message_section(struct ceph_connection *con,
                                         struct kvec *section,
                                         unsigned int sec_len, u32 *crc)
@@ -2672,7 +2700,12 @@ more:
                         prepare_read_tag(con);
                 goto more;
         }
-        if (con->in_tag == CEPH_MSGR_TAG_ACK) {
+        if (con->in_tag == CEPH_MSGR_TAG_ACK ||
+            con->in_tag == CEPH_MSGR_TAG_SEQ) {
+                /*
+                 * the final handshake seq exchange is semantically
+                 * equivalent to an ACK
+                 */
                 ret = read_partial_ack(con);
                 if (ret <= 0)
                         goto out;