********************************
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RDMA Network Block Device (RNBD)
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********************************
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Introduction
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------------
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RNBD (RDMA Network Block Device) is a pair of kernel modules
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(client and server) that allow for remote access of a block device on
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the server over RTRS protocol using the RDMA (InfiniBand, RoCE, iWARP)
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transport. After being mapped, the remote block devices can be accessed
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on the client side as local block devices.
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I/O is transferred between client and server by the RTRS transport
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modules. The administration of RNBD and RTRS modules is done via
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sysfs entries.
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Requirements
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------------
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RTRS kernel modules
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Quick Start
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-----------
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Server side:
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# modprobe rnbd_server
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Client side:
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# modprobe rnbd_client
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# echo "sessname=blya path=ip:10.50.100.66 device_path=/dev/ram0" > \
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/sys/devices/virtual/rnbd-client/ctl/map_device
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Where "sessname=" is a session name, a string to identify the session
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on client and on server sides; "path=" is a destination IP address or
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a pair of a source and a destination IPs, separated by comma. Multiple
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"path=" options can be specified in order to use multipath (see RTRS
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description for details); "device_path=" is the block device to be
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mapped from the server side. After the session to the server machine is
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established, the mapped device will appear on the client side under
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/dev/rnbd<N>.
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RNBD-Server Module Parameters
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=============================
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dev_search_path
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---------------
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When a device is mapped from the client, the server generates the path
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to the block device on the server side by concatenating dev_search_path
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and the "device_path" that was specified in the map_device operation.
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The default dev_search_path is: "/".
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dev_search_path option can also contain %SESSNAME% in order to provide
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different device namespaces for different sessions. See "device_path"
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option for details.
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============================
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Protocol (rnbd/rnbd-proto.h)
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============================
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1. Before mapping first device from a given server, client sends an
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RNBD_MSG_SESS_INFO to the server. Server responds with
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RNBD_MSG_SESS_INFO_RSP. Currently the messages only contain the protocol
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version for backward compatibility.
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2. Client requests to open a device by sending RNBD_MSG_OPEN message. This
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contains the path to the device and access mode (read-only or writable).
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Server responds to the message with RNBD_MSG_OPEN_RSP. This contains
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a 32 bit device id to be used for IOs and device "geometry" related
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information: side, max_hw_sectors, etc.
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3. Client attaches RNBD_MSG_IO to each IO message send to a device. This
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message contains device id, provided by server in his rnbd_msg_open_rsp,
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sector to be accessed, read-write flags and bi_size.
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4. Client closes a device by sending RNBD_MSG_CLOSE which contains only the
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device id provided by the server.
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=========================================
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Contributors List(in alphabetical order)
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=========================================
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Danil Kipnis <danil.kipnis@profitbricks.com>
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Fabian Holler <mail@fholler.de>
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Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
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Jack Wang <jinpu.wang@profitbricks.com>
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Kleber Souza <kleber.souza@profitbricks.com>
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Lutz Pogrell <lutz.pogrell@cloud.ionos.com>
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Milind Dumbare <Milind.dumbare@gmail.com>
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Roman Penyaev <roman.penyaev@profitbricks.com>
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