Ubuntu Manpage: rxrpc - Linux RxRPC (AFS) protocol implementation

NAME

       rxrpc - Linux RxRPC (AFS) protocol implementation

SYNOPSIS

       #include <sys/socket.h>
       #include <linux/rxrpc.h>

       socket = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
       socket = socket(AF_RXRPC, SOCK_DGRAM, PF_INET6);

DESCRIPTION

Linux optionally implements the RxRPC transport protocol, as used by the AFS network filesystem. Both
client and server ends are support - even on the same socket - and authentication is supported at both
ends.

This can be used through the BSD socket interface, using the sendmsg(2) and recvmsg(2) system calls with
control data to multiplex calls over the socket and to provide or retrieve call metadata. request_key(2)
is used to find the authentication keys to use in the calling process's keyrings.

The AF_RXRPC driver uses udp(7) sockets underneath, either IPv4-only or IPv6 (with IPv4), for transport.
Under certain circumstances, the underlying transport sockets may be shared between client-only sockets
(but are never shared if a socket is implementing a server).

Address format
struct sockaddr_rxrpc {
sa_family_t srx_family; /* AF_RXRPC */
uint16_t srx_service; /* The service identifier */
uint16_t transport_type; /* The type of transport */
uint16_t transport_len; /* Transport address length */
union {
sa_family_t family; /* Transport address family */
struct sockaddr_in sin; /* IPv4 transport address */
struct sockaddr_in6 sin6; /* IPv6 transport address */
} transport;
};

Where srx_family is always set to AF_RXRPC; srx_service is set to the service ID of the desired service;
transport_type is set to the transport type, which is always SOCK_DGRAM for now; transport_len says how
big the address in transport is.

Inside the transport address part, and appropriate address for the underlying socket should be set,
including things like family, port and address as appropriate. Note that it may be permissible to use
IPv4 addresses on an IPv6 socket.

Socket Options
AF_RXRPC provides a number of socket options that can be set with setsockopt(2) and read with
getsockopt(2). The socket option level for IPv6 is SOL_RXRPC.

RXRPC_SECURITY_KEY
The option value is a string that specifies the name of a key to pass to request_key(2) to get an
appropriate authentication key. Such keys are expected to be of rxrpc type.

If this isn't set, AF_RXRPC will perform an unauthenticated, unencrypted call to the server.

RXRPC_SECURITY_KEYRING
The option value is a string that specifies the name of a keyring to pass to request_key(2) to
specify the keys used by the server end to authenticate connections.

The service keys in the ring should be of type rxrpc_s and their descriptions should be of the
form "<service-id>:<security-index>" and each should be given an 8-byte secret.

RXRPC_EXCLUSIVE_CONNECTION
The option value should be empty. This causes each call made on this socket to get its own
virtual connection and thus its own negotiated security context.

RXRPC_MIN_SECURITY_LEVEL
The option value should be a 4-byte unsigned integer. This can be one of the following constants:
RXRPC_SECURITY_PLAIN, RXRPC_SECURITY_AUTH or RXRPC_SECURITY_ENCRYPT; the first indicating the
packets should be securely checksummed only, the second that packets should be authenticated and
the third that full encryption should be employed.

RXRPC_UPGRADEABLE_SERVICE
The option value should be a 2-slot array of 2-byte unsigned integers. To use this, the socket
must be a server socket and must have been bound to more than one address with different
srx_service specifiers.

Slot[0] in the array specified the service ID to upgrade from; slot[1] specifies the service ID to
upgrade to. This allows a client to find out if there's a 'better' version of the service
available on the same address, but a different service ID.

If the client follows the correct protocol for probing an upgradeable service, the kernel will
automatically upgrade the service ID on the connection and this will be reflected in the address
returned by recvmsg(2).

RXRPC_SUPPORTED_CMSG
The option buffer should have room for a 4-byte integer. The maximum control buffer message type
supported by the kernel is written into the buffer. This allows an application to find out what
control messages it may use so that it can avoid getting an error if it tries to use something
unsupported.

Message flags
AF_RXRPC communicates certain information by way of the message flags passed to and received from
sendmsg(2) and recvmsg(2).

MSG_MORE
This is passed to sendmsg() to indicate that there is more data to be transmitted as part of the
request phase of a client call or the reply phase of a service operation. MSG_EOR recvmsg() sets
this to indicate that the call has been terminated (the control messages must be parsed for
information as to why) and that the kernel has discarded the user call ID tag. The tag may now be
reused. MSG_PEEK This is passed to recvmsg() to look at the front of the message queue without
removing any messages or changing the state of any outstanding calls. MSG_WAITALL This is passed
to sendmsg() to instruct it not to return for a signal if it is still loading up the message queue
and progress is being made at the other side in emptying it. This works around the problem of
sendmsg() getting interrupted after partially queuing its data, but not then being able to return
how much it has consumed. MSG_DONTWAIT This is passed to recvmsg() to indicate that it shouldn't
wait if the message queue is empty.

Control messages
AF_RXRPC communicates metadata to the caller through the ancillary data buffer (msg_control) in the
messages passed to and fro using sendmsg(2) and recvmsg(2). When building a control message buffer for
sendmsg(), the RXRPC_SUPPORTED_CMSG value should be consulted to make sure that the control message type
is supported.

RXRPC_USER_CALL_ID
The data for this is an arbitrary long integer/pointer-sized tag that represents the call to the
kernel. It may, for example, hold a pointer to some userspace structure representing the call to
the process.

[sendmsg] This is passed to sendmsg() when the message proposed will create a client call. It
must thereafter be included in all future sendmsg() calls pertaining to that call.

[recvmsg] recvmsg() includes the tag in all messages pertaining to a call until the final
termination message is reached - which recvmsg() will mark by setting MSG_EOR.

RXRPC_ABORT
The data for this is a 32-bit integer that is the abort code.

[sendmsg] When passed to sendmsg(), this causes the operation matching the tag to be aborted; this
will be followed up by recvmsg() indicating MSG_EOR and a local error of ECONNABORTED, thereby
terminating the tag.

[recvmsg] When obtained from recvmsg(), this indicates that a remote abort was received from the
peer and the data gives the code for that abort.

RXRPC_ACK
[recvmsg] This conveys no data. It indicates the final acknowledgement to a service call has been
received.

RXRPC_NET_ERROR
[recvmsg] This conveys a 32-bit integer into which the network error that terminated a call will
have been placed.

RXRPC_BUSY
[recvmsg] This conveys no data. It indicates that the operation has been rejected because the
server is busy.

RXRPC_LOCAL_ERROR
[recvmsg] This conveys a 32-bit integer into which the local error that terminated a call will
have been placed.

RXRPC_NEW_CALL
[recvmsg] This conveys no data. It indicates that a new service call has arrived at a server
socket and is in need of a tag. RXRPC_ACCEPT is must be used for that.

RXRPC_ACCEPT
The data for this is an arbitrary long integer/pointer-sized tag that represents the call to the
kernel with the same semantics as for RXRPC_USER_CALL_ID.

[sendmsg] Supply a user call ID tag to a new service call.

RXRPC_EXCLUSIVE_CALL
[sendmsg] Indicate that this particular call should be made on its own connection with an unshared
negotiated security context. This requires no additional data.

RXRPC_UPGRADE_SERVICE
[sendmsg] Indicate that this call should attempt to probe the service ID on the other side to see
if it gets upgraded. The answer can be found in the srx_service value of the peer address
recvmsg() returns for this call. This requires no additional data.

RXRPC_TX_LENGTH
The data for this is a signed 64-bit integer.

[sendmsg] Specify the exact total transmit size. This allows AF_RXRPC to work out in advance how
big encrypted packets are going to be (under some circumstances, there's a data length encrypted
inside the packet).

If this is set, it may allow AF_RXRPC to be more efficient at filling packets. If the wrong
amount of data is given (too little or too much), then the call will be aborted.

RXRPC_SET_CALL_TIMEOUT
The data for this is an array of 1-3 32-bit integers.

[sendmsg] Specify various call timeouts. The first timeout is the hard timeout for the call in
seconds: the call will be aborted if it takes longer than this amount of time in total.

The second timeout is the idle timeout for the call in milliseconds: the call will be aborted if
we don't receive the next DATA packet within that amount of time during the reception phase.

The third timeout is the normal timeout for the call in milliseconds: the call will be aborted if
we go for that amount of time without receiving any type of packet pertaining to the call.

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO