BRMR Message Protocol

BRMR currently has a small set of commands being exchanged between the client and server side. These are map, unmap, and metadata read. These commands use the rmr_id_t.b field to inform the server of their presence. This is undesirable because the rmr_id_t struct is reserved for use with IOs only. To solve this issue, a proper protocol with command and message structs has been added.

Message types

BRMR will have 2 message types: Command and IO (used as appropriate). These will be stored in brmr_msg_hdr.type.

For the command message type, BRMR will have a struct brmr_msg_cmd, which represents all commands. The cmd_type field stores which command it is. A union holds structs with command-specific data.

Command types

The following command types will exist for now (not all are currently used):

BRMR_CMD_MAP_NEW — Map a new device BRMR_CMD_MAP_CHECK — Try to map an already-mapped device BRMR_CMD_UNMAP — Unmap a device BRMR_CMD_READ_MD — Read metadata BRMR_CMD_RSP — Represents a command response (buffer) sent back from the server side

The IO message type is used to send IOs. The message stores fields related to IO, such as flags, sector, and offset. This is not currently used but will be added in the future.