__le32 segment length
__le16 segment alignment
} * 4
- reserved (2 bytes)
+ __u8 flags
+ reserved (1 byte)
__le32 preamble crc
An empty frame has one empty segment. A non-empty frame can have
If there are less than four segments, unused (trailing) segment
length and segment alignment fields are zeroed.
+### Currently supported flags
+
+ 1. FRAME_EARLY_DATA_COMPRESSED (see :ref:`msgr-post-compression`)
+
The reserved bytes are zeroed.
The preamble checksum is CRC32-C. It covers everything up to
late_status has the same meaning as in msgr2.1-crc mode.
+Compression
+-----------
+Compression handshake is implemented using msgr2 feature-based handshaking.
+In this phase, the client will indicate the server if on-wire-compression can be used for message transmitting,
+in addition to the list of supported compression methods. If on-wire-compression is enabled for both client and server,
+the server will choose a compression method based on client's request and its' own preferences.
+Once the handshake is completed, both peers have setup their compression handlers (if desired).
+
+* TAG_COMPRESSION_REQUEST (client->server): declares compression capabilities and requirements::
+
+ bool is_compress
+ std::vector<uint32_t> preferred_methods
+
+ - if the client identifies that both peers support compression feature, it initiates the handshake.
+ - is_compress flag indicates whether the client's configuration is to use compression.
+ - preferred_methods is a list of compression algorithms that are supported by the client.
+
+* TAG_COMPRESSION_DONE (server->client) : determines on compression settings::
+
+ bool is_compress
+ uint32_t method
+
+ - the server determines whether compression is possible according to its' configuration.
+ - if it is possible, it will pick its' most prioritizied compression method that is also supprorted by the client.
+ - if none exists, it will determine that session between the peers will be handled without compression.
+
+.. ditaa::
+
+ +---------+ +--------+
+ | Client | | Server |
+ +---------+ +--------+
+ | compression request |
+ |----------------------->|
+ |<-----------------------|
+ | compression done |
+
+# msgr2.x-secure mode
+
+Combining compression with encryption introduces security implications.
+Compression will not be possible when using secure mode, unless configured specifically by an admin.
+
+.. _msgr-post-compression:
+
+Post-compression frame format
+-----------------------------
+Depending on the negotiated connection mode from TAG_COMPRESSION_DONE, the connection is able to accept/send compressed frames or process all frames as decompressed.
+
+# msgr2.x-force mode
+
+All subsequent frames that will be sent via the connection will be compressed if compression requirements are met (e.g, the frames size).
+
+For compressed frames, the sending peer will enable the FRAME_EARLY_DATA_COMPRESSED flag, thus allowing the accepting peer to detect it and decompress the frame.
+
+# msgr2.x-none mode
+
+FRAME_EARLY_DATA_COMPRESSED flag will be disabled in preamble.
+
+
Message flow handshake
----------------------
| |
+.. graphviz::
+ :caption: client side state machine
+
+ digraph lossy_client {
+ node [shape = doublecircle]; "start_connect" "closed";
+ node [shape = oval];
+ start_connect -> banner_connecting [label = "<connected>"];
+ subgraph hello_banner {
+ banner_connecting -> hello_connecting [label = "banner exchange"];
+ hello_connecting -> banner_connecting [label = "hello exchange"];
+ label = "hello banner exchange";
+ color = blue;
+ }
+ banner_connecting -> auth_connecting [label = "<exchange done>"];
+ auth_connecting -> auth_connecting [label = "auth reply more"];
+ auth_connecting -> auth_connecting [label = "auth bad method"];
+ auth_connecting -> auth_connecting_sign [label = "auth done"];
+ auth_connecting_sign -> session_connecting [label = "auth signature"];
+ session_connecting -> wait [label = "wait"];
+ wait -> start_connect [label = "<backoff>"];
+ session_connecting -> closed [label = "ident missing features"];
+ session_connecting -> ready [label = "server ident", tooltip = "set peer_name, peer_addr and connection features"];
+ ready -> ready [label = "keep alive"];
+ }
+
+.. graphviz::
+ :caption: server side state machine
+
+ digraph lossy_server {
+ node [shape = doublecircle]; "start_accept" "closed";
+ node [shape = oval];
+ start_accept -> banner_accepting [label = "<accepted>"];
+ subgraph hello_banner {
+ banner_accepting -> hello_accepting [label = "banner exchange"];
+ hello_accepting -> banner_accepting [label = "hello exchange"];
+ label = "hello banner exchange";
+ color = blue;
+ };
+ banner_accepting -> auth_accepting [label = "<exchange done>"];
+ auth_accepting -> auth_accepting_more [label = "auth_request => 0"];
+ auth_accepting -> auth_accepting_sign [label = "auth_request => 1"];
+ auth_accepting_more -> auth_accepting_more [label = "auth_request => 0"];
+ auth_accepting_more -> auth_accepting_sign [label = "auth_request => 1"];
+ auth_accepting_more -> standby [label = "auth_request => EBUSY"];
+ auth_accepting_more -> auth_accepting_more [label = "auth_request => *"];
+ auth_accepting -> standby [label = "auth_request => EBUSY"];
+ auth_accepting -> auth_accepting [label = "send <auth bad method>"];
+ auth_accepting_sign -> session_accepting [label = "auth signature"];
+ session_accepting -> session_accepting [label = "reconnect"];
+ session_accepting -> closed [label = "ident missing features"];
+ session_accepting -> ready [label = "client ident", tooltip = "set connection features"];
+ ready -> ready [label = "keep alive"];
+ }
projects / ceph.git / blobdiff