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+What: /sys/class/rnbd-client
+Date: Feb 2020
+KernelVersion: 5.7
+Contact: Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description: Provide information about RNBD-client.
+ All sysfs files that are not read-only provide the usage information on read:
+
+ Example::
+
+ # cat /sys/class/rnbd-client/ctl/map_device
+
+ > Usage: echo "sessname=<name of the rtrs session> path=<[srcaddr,]dstaddr>
+ > [path=<[srcaddr,]dstaddr>] device_path=<full path on remote side>
+ > [access_mode=<ro|rw|migration>] > map_device
+ >
+ > addr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]
+
+What: /sys/class/rnbd-client/ctl/map_device
+Date: Feb 2020
+KernelVersion: 5.7
+Contact: Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description: Expected format is the following::
+
+ sessname=<name of the rtrs session>
+ path=<[srcaddr,]dstaddr> [path=<[srcaddr,]dstaddr> ...]
+ device_path=<full path on remote side>
+ [access_mode=<ro|rw|migration>]
+
+ Where:
+
+ sessname:
+ accepts a string not bigger than 256 chars, which identifies
+ a given session on the client and on the server.
+ I.e. "clt_hostname-srv_hostname" could be a natural choice.
+
+ path:
+ describes a connection between the client and the server by
+ specifying destination and, when required, the source address.
+ The addresses are to be provided in the following format::
+
+ ip:<IPv6>
+ ip:<IPv4>
+ gid:<GID>
+
+ for example::
+
+ path=ip:10.0.0.66
+
+ The single addr is treated as the destination.
+ The connection will be established to this server from any client IP address.
+
+ ::
+
+ path=ip:10.0.0.66,ip:10.0.1.66
+
+ First addr is the source address and the second is the destination.
+
+ If multiple "path=" options are specified multiple connection
+ will be established and data will be sent according to
+ the selected multipath policy (see RTRS mp_policy sysfs entry description).
+
+ device_path:
+ Path to the block device on the server side. Path is specified
+ relative to the directory on server side configured in the
+ 'dev_search_path' module parameter of the rnbd_server.
+ The rnbd_server prepends the <device_path> received from client
+ with <dev_search_path> and tries to open the
+ <dev_search_path>/<device_path> block device. On success,
+ a /dev/rnbd<N> device file, a /sys/block/rnbd<N>/
+ directory and an entry in /sys/class/rnbd-client/ctl/devices
+ will be created.
+
+ If 'dev_search_path' contains '%SESSNAME%', then each session can
+ have different devices namespace, e.g. server was configured with
+ the following parameter "dev_search_path=/run/rnbd-devs/%SESSNAME%",
+ client has this string "sessname=blya device_path=sda", then server
+ will try to open: /run/rnbd-devs/blya/sda.
+
+ access_mode:
+ the access_mode parameter specifies if the device is to be
+ mapped as "ro" read-only or "rw" read-write. The server allows
+ a device to be exported in rw mode only once. The "migration"
+ access mode has to be specified if a second mapping in read-write
+ mode is desired.
+
+ By default "rw" is used.
+
+ nr_poll_queues
+ specifies the number of poll-mode queues. If the IO has HIPRI flag,
+ the block-layer will send the IO via the poll-mode queue.
+ For fast network and device the polling is faster than interrupt-base
+ IO handling because it saves time for context switching, switching to
+ another process, handling the interrupt and switching back to the
+ issuing process.
+
+ Set -1 if you want to set it as the number of CPUs
+ By default rnbd client creates only irq-mode queues.
+
+ NOTICE: MUST make a unique session for a device using the poll-mode queues.
+
+ Exit Codes:
+
+ If the device is already mapped it will fail with EEXIST. If the input
+ has an invalid format it will return EINVAL. If the device path cannot
+ be found on the server, it will fail with ENOENT.
+
+ Finding device file after mapping
+ ---------------------------------
+
+ After mapping, the device file can be found by:
+ o The symlink /sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>
+ points to /sys/block/<dev-name>. The last part of the symlink destination
+ is the same as the device name. By extracting the last part of the
+ path the path to the device /dev/<dev-name> can be build.
+
+ * /dev/block/$(cat /sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>/dev)
+
+ How to find the <device_id> of the device is described on the next
+ section.
+
+What: /sys/class/rnbd-client/ctl/devices/
+Date: Feb 2020
+KernelVersion: 5.7
+Contact: Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description: For each device mapped on the client a new symbolic link is created as
+ /sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>, which points
+ to the block device created by rnbd (/sys/block/rnbd<N>/).
+ The <device_id> of each device is created as follows:
+
+ - If the 'device_path' provided during mapping contains slashes ("/"),
+ they are replaced by exclamation mark ("!") and used as as the
+ <device_id>. Otherwise, the <device_id> will be the same as the
+ "device_path" provided.