--- /dev/null
+==================
+ Network Protocol
+==================
+
+This file describes the network protocol used by Ceph. In order to understand
+the way the structures are defined it is recommended to read the introduction
+of :doc:`/dev/network-encoding` first.
+
+Hello
+=====
+
+The protocol starts with a handshake that confirms that both nodes are talking
+ceph and shares some basic information.
+
+Banner
+------
+
+The first action is the server sending banner to the client. The banner is
+defined in ``CEPH_BANNER`` from ``src/include/msgr.h``. This is followed by
+the server's then client's address each encoded as a ``entity_addr_t``.
+
+Once the client verifies that the servers banner matches its own it replies with
+its banner and its address.
+
+Connect
+-------
+
+Once the banners have been verified and the addresses exchanged the connection
+negotiation begins. First the client sends a ``ceph_msg_connect`` structure
+with its information.
+
+::
+
+ // From src/include/msgr.h
+ struct ceph_msg_connect {
+ u64le features; // Supported features (CEPH_FEATURE_*)
+ u32le host_type; // CEPH_ENTITY_TYPE_*
+ u32le global_seq; // Number of connections initiated by this host.
+ u32le connect_seq; // Number of connections initiated in this session.
+ u32le protocol_version;
+ u32le authorizer_protocol;
+ u32le authorizer_len;
+ u8 flags; // CEPH_MSG_CONNECT_*
+ u8 authorizer[authorizer_len];
+ }
+
+Connect Reply
+-------------
+
+Once the connect has been sent the connection has effectively been opened,
+however the first message the server sends must be a connect reply message.
+
+::
+
+ struct ceph_msg_connect_reply {
+ u8 tag; // Tag indicating response code.
+ u64le features;
+ u32le global_seq;
+ u32le connect_seq;
+ u32le protocol_version;
+ u32le authorizer_len;
+ u8 flags;
+ u8 authorizer[authorizer_len];
+ }
+
+MSGR Protocol
+=============
+
+This is a low level protocol over which messages are delivered. The messages
+at this level consist of a tag byte, identifying the type of message, followed
+by the message data.
+
+::
+
+ // Virtual structure.
+ struct {
+ u8 tag; // CEPH_MSGR_TAG_*
+ u8 data[]; // Length depends on tag and data.
+ }
+
+The length of ``data`` is determined by the tag byte and depending on the
+message type via information in the ``data`` array itself.
+
+.. note::
+ There is no way to determine the length of the message if you do not
+ understand the type of message.
+
+The message tags are defined in ``src/include/msgr.h`` and the current ones
+are listed below along with the data they include. Note that the defined
+structures don't exist in the source and are merely for representing the
+protocol.
+
+CEPH_MSGR_TAG_CLOSE (0x06)
+--------------------------
+
+::
+
+ struct ceph_msgr_close {
+ u8 tag = 0x06;
+ u8 data[0]; // No data.
+ }
+
+The close message indicates that the connection is being closed.
+
+CEPH_MSGR_TAG_MSG (0x07)
+------------------------
+
+::
+
+ struct ceph_msgr_msg {
+ u8 tag = 0x07;
+ ceph_msg_header header;
+ u8 front [header.front_len ];
+ u8 middle[header.middle_len];
+ u8 data [header.data_len ];
+ ceph_msg_footer footer;
+ }
+
+ // From src/include/msgr.h
+ struct ceph_msg_header {
+ u64le seq; // Sequence number.
+ u64le tid; // Transaction ID.
+ u16le type; // Message type (CEPH_MSG_* or MSG_*).
+ u16le priority; // Priority (higher is more important).
+ u16le version; // Version of message encoding.
+
+ u32le front_len; // The size of the front section.
+ u32le middle_len; // The size of the middle section.
+ u32le data_len; // The size of the data section.
+ u16le data_off; // The way data should be aligned by the reciever.
+
+ ceph_entity_name src; // Information about the sender.
+
+ u16le compat_version; // Oldest compatible encoding version.
+ u16le reserved; // Unused.
+ u32le crc; // CRC of header.
+ }
+
+ // From src/include/msgr.h
+ struct ceph_msg_footer {
+ u32le front_crc; // Checksums of the various sections.
+ u32le middle_crc; //
+ u32le data_crc; //
+ u64le sig; // Crypographic signature.
+ u8 flags;
+ }
+
+Messages are the business logic of Ceph. They are what is used to send data and
+requests between nodes. The message header contains the length of the message
+so unknown messages can be handled gracefully.
+
+There are two names for the message type constants ``CEPH_MSG_*`` and ``MSG_*``.
+The only difference between the two is that the first are considered "public"
+while the second is for internal use only. There is no protocol-level
+difference.
+
+CEPH_MSGR_TAG_ACK (0x08)
+------------------------
+
+::
+
+ struct ceph_msgr_ack {
+ u8 tag = 0x08;
+ u64le seq; // The sequence number of the message being acknowledged.
+ }
+
+CEPH_MSGR_TAG_KEEPALIVE (0x09)
+------------------------------
+
+::
+
+ struct ceph_msgr_keepalive {
+ u8 tag = 0x09;
+ u8 data[0]; // No data.
+ }
+
+CEPH_MSGR_TAG_KEEPALIVE2 (0x0E)
+-------------------------------
+
+::
+
+ struct ceph_msgr_keepalive2 {
+ u8 tag = 0x0E;
+ utime_t timestamp;
+ }
+
+CEPH_MSGR_TAG_KEEPALIVE2_ACK (0x0F)
+-----------------------------------
+
+::
+
+ struct ceph_msgr_keepalive2_ack {
+ u8 tag = 0x0F;
+ utime_t timestamp;
+ }
+
+.. vi: textwidth=80 noexpandtab
Code Review / stor4nfv.git / blobdiff