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b960a34b73
Allow kernel services using AF_RXRPC to indicate that a call should be non-interruptible. This allows kafs to make things like lock-extension and writeback data storage calls non-interruptible. If this is set, signals will be ignored for operations on that call where possible - such as waiting to get a call channel on an rxrpc connection. It doesn't prevent UDP sendmsg from being interrupted, but that will be handled by packet retransmission. rxrpc_kernel_recv_data() isn't affected by this since that never waits, preferring instead to return -EAGAIN and leave the waiting to the caller. Userspace initiated calls can't be set to be uninterruptible at this time. Signed-off-by: David Howells <dhowells@redhat.com>
1156 lines
45 KiB
Plaintext
1156 lines
45 KiB
Plaintext
======================
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RxRPC NETWORK PROTOCOL
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======================
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The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
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that can be used to perform RxRPC remote operations. This is done over sockets
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of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and
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receive data, aborts and errors.
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Contents of this document:
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(*) Overview.
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(*) RxRPC protocol summary.
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(*) AF_RXRPC driver model.
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(*) Control messages.
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(*) Socket options.
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(*) Security.
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(*) Example client usage.
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(*) Example server usage.
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(*) AF_RXRPC kernel interface.
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(*) Configurable parameters.
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========
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OVERVIEW
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========
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RxRPC is a two-layer protocol. There is a session layer which provides
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reliable virtual connections using UDP over IPv4 (or IPv6) as the transport
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layer, but implements a real network protocol; and there's the presentation
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layer which renders structured data to binary blobs and back again using XDR
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(as does SunRPC):
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+-------------+
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| Application |
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+-------------+
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| XDR | Presentation
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+-------------+
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| RxRPC | Session
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+-------------+
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| UDP | Transport
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+-------------+
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AF_RXRPC provides:
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(1) Part of an RxRPC facility for both kernel and userspace applications by
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making the session part of it a Linux network protocol (AF_RXRPC).
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(2) A two-phase protocol. The client transmits a blob (the request) and then
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receives a blob (the reply), and the server receives the request and then
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transmits the reply.
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(3) Retention of the reusable bits of the transport system set up for one call
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to speed up subsequent calls.
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(4) A secure protocol, using the Linux kernel's key retention facility to
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manage security on the client end. The server end must of necessity be
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more active in security negotiations.
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AF_RXRPC does not provide XDR marshalling/presentation facilities. That is
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left to the application. AF_RXRPC only deals in blobs. Even the operation ID
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is just the first four bytes of the request blob, and as such is beyond the
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kernel's interest.
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Sockets of AF_RXRPC family are:
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(1) created as type SOCK_DGRAM;
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(2) provided with a protocol of the type of underlying transport they're going
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to use - currently only PF_INET is supported.
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The Andrew File System (AFS) is an example of an application that uses this and
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that has both kernel (filesystem) and userspace (utility) components.
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======================
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RXRPC PROTOCOL SUMMARY
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======================
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An overview of the RxRPC protocol:
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(*) RxRPC sits on top of another networking protocol (UDP is the only option
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currently), and uses this to provide network transport. UDP ports, for
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example, provide transport endpoints.
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(*) RxRPC supports multiple virtual "connections" from any given transport
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endpoint, thus allowing the endpoints to be shared, even to the same
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remote endpoint.
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(*) Each connection goes to a particular "service". A connection may not go
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to multiple services. A service may be considered the RxRPC equivalent of
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a port number. AF_RXRPC permits multiple services to share an endpoint.
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(*) Client-originating packets are marked, thus a transport endpoint can be
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shared between client and server connections (connections have a
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direction).
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(*) Up to a billion connections may be supported concurrently between one
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local transport endpoint and one service on one remote endpoint. An RxRPC
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connection is described by seven numbers:
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Local address }
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Local port } Transport (UDP) address
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Remote address }
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Remote port }
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Direction
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Connection ID
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Service ID
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(*) Each RxRPC operation is a "call". A connection may make up to four
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billion calls, but only up to four calls may be in progress on a
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connection at any one time.
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(*) Calls are two-phase and asymmetric: the client sends its request data,
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which the service receives; then the service transmits the reply data
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which the client receives.
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(*) The data blobs are of indefinite size, the end of a phase is marked with a
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flag in the packet. The number of packets of data making up one blob may
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not exceed 4 billion, however, as this would cause the sequence number to
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wrap.
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(*) The first four bytes of the request data are the service operation ID.
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(*) Security is negotiated on a per-connection basis. The connection is
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initiated by the first data packet on it arriving. If security is
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requested, the server then issues a "challenge" and then the client
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replies with a "response". If the response is successful, the security is
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set for the lifetime of that connection, and all subsequent calls made
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upon it use that same security. In the event that the server lets a
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connection lapse before the client, the security will be renegotiated if
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the client uses the connection again.
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(*) Calls use ACK packets to handle reliability. Data packets are also
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explicitly sequenced per call.
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(*) There are two types of positive acknowledgment: hard-ACKs and soft-ACKs.
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A hard-ACK indicates to the far side that all the data received to a point
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has been received and processed; a soft-ACK indicates that the data has
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been received but may yet be discarded and re-requested. The sender may
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not discard any transmittable packets until they've been hard-ACK'd.
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(*) Reception of a reply data packet implicitly hard-ACK's all the data
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packets that make up the request.
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(*) An call is complete when the request has been sent, the reply has been
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received and the final hard-ACK on the last packet of the reply has
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reached the server.
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(*) An call may be aborted by either end at any time up to its completion.
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=====================
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AF_RXRPC DRIVER MODEL
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=====================
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About the AF_RXRPC driver:
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(*) The AF_RXRPC protocol transparently uses internal sockets of the transport
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protocol to represent transport endpoints.
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(*) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC
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connections are handled transparently. One client socket may be used to
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make multiple simultaneous calls to the same service. One server socket
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may handle calls from many clients.
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(*) Additional parallel client connections will be initiated to support extra
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concurrent calls, up to a tunable limit.
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(*) Each connection is retained for a certain amount of time [tunable] after
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the last call currently using it has completed in case a new call is made
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that could reuse it.
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(*) Each internal UDP socket is retained [tunable] for a certain amount of
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time [tunable] after the last connection using it discarded, in case a new
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connection is made that could use it.
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(*) A client-side connection is only shared between calls if they have have
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the same key struct describing their security (and assuming the calls
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would otherwise share the connection). Non-secured calls would also be
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able to share connections with each other.
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(*) A server-side connection is shared if the client says it is.
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(*) ACK'ing is handled by the protocol driver automatically, including ping
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replying.
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(*) SO_KEEPALIVE automatically pings the other side to keep the connection
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alive [TODO].
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(*) If an ICMP error is received, all calls affected by that error will be
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aborted with an appropriate network error passed through recvmsg().
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Interaction with the user of the RxRPC socket:
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(*) A socket is made into a server socket by binding an address with a
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non-zero service ID.
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(*) In the client, sending a request is achieved with one or more sendmsgs,
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followed by the reply being received with one or more recvmsgs.
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(*) The first sendmsg for a request to be sent from a client contains a tag to
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be used in all other sendmsgs or recvmsgs associated with that call. The
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tag is carried in the control data.
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(*) connect() is used to supply a default destination address for a client
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socket. This may be overridden by supplying an alternate address to the
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first sendmsg() of a call (struct msghdr::msg_name).
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(*) If connect() is called on an unbound client, a random local port will
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bound before the operation takes place.
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(*) A server socket may also be used to make client calls. To do this, the
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first sendmsg() of the call must specify the target address. The server's
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transport endpoint is used to send the packets.
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(*) Once the application has received the last message associated with a call,
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the tag is guaranteed not to be seen again, and so it can be used to pin
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client resources. A new call can then be initiated with the same tag
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without fear of interference.
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(*) In the server, a request is received with one or more recvmsgs, then the
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the reply is transmitted with one or more sendmsgs, and then the final ACK
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is received with a last recvmsg.
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(*) When sending data for a call, sendmsg is given MSG_MORE if there's more
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data to come on that call.
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(*) When receiving data for a call, recvmsg flags MSG_MORE if there's more
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data to come for that call.
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(*) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg
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to indicate the terminal message for that call.
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(*) A call may be aborted by adding an abort control message to the control
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data. Issuing an abort terminates the kernel's use of that call's tag.
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Any messages waiting in the receive queue for that call will be discarded.
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(*) Aborts, busy notifications and challenge packets are delivered by recvmsg,
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and control data messages will be set to indicate the context. Receiving
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an abort or a busy message terminates the kernel's use of that call's tag.
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(*) The control data part of the msghdr struct is used for a number of things:
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(*) The tag of the intended or affected call.
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(*) Sending or receiving errors, aborts and busy notifications.
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(*) Notifications of incoming calls.
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(*) Sending debug requests and receiving debug replies [TODO].
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(*) When the kernel has received and set up an incoming call, it sends a
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message to server application to let it know there's a new call awaiting
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its acceptance [recvmsg reports a special control message]. The server
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application then uses sendmsg to assign a tag to the new call. Once that
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is done, the first part of the request data will be delivered by recvmsg.
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(*) The server application has to provide the server socket with a keyring of
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secret keys corresponding to the security types it permits. When a secure
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connection is being set up, the kernel looks up the appropriate secret key
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in the keyring and then sends a challenge packet to the client and
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receives a response packet. The kernel then checks the authorisation of
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the packet and either aborts the connection or sets up the security.
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(*) The name of the key a client will use to secure its communications is
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nominated by a socket option.
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Notes on sendmsg:
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(*) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is
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making progress at accepting packets within a reasonable time such that we
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manage to queue up all the data for transmission. This requires the
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client to accept at least one packet per 2*RTT time period.
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If this isn't set, sendmsg() will return immediately, either returning
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EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data
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consumed.
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Notes on recvmsg:
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(*) If there's a sequence of data messages belonging to a particular call on
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the receive queue, then recvmsg will keep working through them until:
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(a) it meets the end of that call's received data,
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(b) it meets a non-data message,
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(c) it meets a message belonging to a different call, or
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(d) it fills the user buffer.
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If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
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reception of further data, until one of the above four conditions is met.
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(2) MSG_PEEK operates similarly, but will return immediately if it has put any
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data in the buffer rather than sleeping until it can fill the buffer.
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(3) If a data message is only partially consumed in filling a user buffer,
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then the remainder of that message will be left on the front of the queue
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for the next taker. MSG_TRUNC will never be flagged.
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(4) If there is more data to be had on a call (it hasn't copied the last byte
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of the last data message in that phase yet), then MSG_MORE will be
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flagged.
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================
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CONTROL MESSAGES
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================
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AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
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calls, to invoke certain actions and to report certain conditions. These are:
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MESSAGE ID SRT DATA MEANING
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======================= === =========== ===============================
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RXRPC_USER_CALL_ID sr- User ID App's call specifier
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RXRPC_ABORT srt Abort code Abort code to issue/received
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RXRPC_ACK -rt n/a Final ACK received
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RXRPC_NET_ERROR -rt error num Network error on call
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RXRPC_BUSY -rt n/a Call rejected (server busy)
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RXRPC_LOCAL_ERROR -rt error num Local error encountered
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RXRPC_NEW_CALL -r- n/a New call received
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RXRPC_ACCEPT s-- n/a Accept new call
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RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call
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RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded
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RXRPC_TX_LENGTH s-- data len Total length of Tx data
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(SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
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(*) RXRPC_USER_CALL_ID
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This is used to indicate the application's call ID. It's an unsigned long
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that the app specifies in the client by attaching it to the first data
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message or in the server by passing it in association with an RXRPC_ACCEPT
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message. recvmsg() passes it in conjunction with all messages except
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those of the RXRPC_NEW_CALL message.
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(*) RXRPC_ABORT
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This is can be used by an application to abort a call by passing it to
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sendmsg, or it can be delivered by recvmsg to indicate a remote abort was
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received. Either way, it must be associated with an RXRPC_USER_CALL_ID to
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specify the call affected. If an abort is being sent, then error EBADSLT
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will be returned if there is no call with that user ID.
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(*) RXRPC_ACK
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This is delivered to a server application to indicate that the final ACK
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of a call was received from the client. It will be associated with an
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RXRPC_USER_CALL_ID to indicate the call that's now complete.
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(*) RXRPC_NET_ERROR
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This is delivered to an application to indicate that an ICMP error message
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was encountered in the process of trying to talk to the peer. An
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errno-class integer value will be included in the control message data
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indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
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affected.
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(*) RXRPC_BUSY
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This is delivered to a client application to indicate that a call was
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rejected by the server due to the server being busy. It will be
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associated with an RXRPC_USER_CALL_ID to indicate the rejected call.
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(*) RXRPC_LOCAL_ERROR
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This is delivered to an application to indicate that a local error was
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encountered and that a call has been aborted because of it. An
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errno-class integer value will be included in the control message data
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indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
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affected.
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(*) RXRPC_NEW_CALL
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This is delivered to indicate to a server application that a new call has
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arrived and is awaiting acceptance. No user ID is associated with this,
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as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT.
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(*) RXRPC_ACCEPT
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This is used by a server application to attempt to accept a call and
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assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID
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to indicate the user ID to be assigned. If there is no call to be
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accepted (it may have timed out, been aborted, etc.), then sendmsg will
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return error ENODATA. If the user ID is already in use by another call,
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then error EBADSLT will be returned.
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(*) RXRPC_EXCLUSIVE_CALL
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This is used to indicate that a client call should be made on a one-off
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connection. The connection is discarded once the call has terminated.
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(*) RXRPC_UPGRADE_SERVICE
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This is used to make a client call to probe if the specified service ID
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may be upgraded by the server. The caller must check msg_name returned to
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recvmsg() for the service ID actually in use. The operation probed must
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be one that takes the same arguments in both services.
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Once this has been used to establish the upgrade capability (or lack
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thereof) of the server, the service ID returned should be used for all
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future communication to that server and RXRPC_UPGRADE_SERVICE should no
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longer be set.
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(*) RXRPC_TX_LENGTH
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This is used to inform the kernel of the total amount of data that is
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going to be transmitted by a call (whether in a client request or a
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service response). If given, it allows the kernel to encrypt from the
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userspace buffer directly to the packet buffers, rather than copying into
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the buffer and then encrypting in place. This may only be given with the
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first sendmsg() providing data for a call. EMSGSIZE will be generated if
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the amount of data actually given is different.
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This takes a parameter of __s64 type that indicates how much will be
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transmitted. This may not be less than zero.
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The symbol RXRPC__SUPPORTED is defined as one more than the highest control
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message type supported. At run time this can be queried by means of the
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RXRPC_SUPPORTED_CMSG socket option (see below).
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==============
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SOCKET OPTIONS
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==============
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AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:
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(*) RXRPC_SECURITY_KEY
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This is used to specify the description of the key to be used. The key is
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extracted from the calling process's keyrings with request_key() and
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should be of "rxrpc" type.
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The optval pointer points to the description string, and optlen indicates
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how long the string is, without the NUL terminator.
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(*) RXRPC_SECURITY_KEYRING
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Similar to above but specifies a keyring of server secret keys to use (key
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type "keyring"). See the "Security" section.
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(*) RXRPC_EXCLUSIVE_CONNECTION
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This is used to request that new connections should be used for each call
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made subsequently on this socket. optval should be NULL and optlen 0.
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(*) RXRPC_MIN_SECURITY_LEVEL
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This is used to specify the minimum security level required for calls on
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this socket. optval must point to an int containing one of the following
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values:
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(a) RXRPC_SECURITY_PLAIN
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Encrypted checksum only.
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(b) RXRPC_SECURITY_AUTH
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Encrypted checksum plus packet padded and first eight bytes of packet
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encrypted - which includes the actual packet length.
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(c) RXRPC_SECURITY_ENCRYPTED
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Encrypted checksum plus entire packet padded and encrypted, including
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actual packet length.
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(*) RXRPC_UPGRADEABLE_SERVICE
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This is used to indicate that a service socket with two bindings may
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upgrade one bound service to the other if requested by the client. optval
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must point to an array of two unsigned short ints. The first is the
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service ID to upgrade from and the second the service ID to upgrade to.
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(*) RXRPC_SUPPORTED_CMSG
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This is a read-only option that writes an int into the buffer indicating
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the highest control message type supported.
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========
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SECURITY
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========
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|
|
Currently, only the kerberos 4 equivalent protocol has been implemented
|
|
(security index 2 - rxkad). This requires the rxkad module to be loaded and,
|
|
on the client, tickets of the appropriate type to be obtained from the AFS
|
|
kaserver or the kerberos server and installed as "rxrpc" type keys. This is
|
|
normally done using the klog program. An example simple klog program can be
|
|
found at:
|
|
|
|
http://people.redhat.com/~dhowells/rxrpc/klog.c
|
|
|
|
The payload provided to add_key() on the client should be of the following
|
|
form:
|
|
|
|
struct rxrpc_key_sec2_v1 {
|
|
uint16_t security_index; /* 2 */
|
|
uint16_t ticket_length; /* length of ticket[] */
|
|
uint32_t expiry; /* time at which expires */
|
|
uint8_t kvno; /* key version number */
|
|
uint8_t __pad[3];
|
|
uint8_t session_key[8]; /* DES session key */
|
|
uint8_t ticket[0]; /* the encrypted ticket */
|
|
};
|
|
|
|
Where the ticket blob is just appended to the above structure.
|
|
|
|
|
|
For the server, keys of type "rxrpc_s" must be made available to the server.
|
|
They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an
|
|
rxkad key for the AFS VL service). When such a key is created, it should be
|
|
given the server's secret key as the instantiation data (see the example
|
|
below).
|
|
|
|
add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
|
|
|
|
A keyring is passed to the server socket by naming it in a sockopt. The server
|
|
socket then looks the server secret keys up in this keyring when secure
|
|
incoming connections are made. This can be seen in an example program that can
|
|
be found at:
|
|
|
|
http://people.redhat.com/~dhowells/rxrpc/listen.c
|
|
|
|
|
|
====================
|
|
EXAMPLE CLIENT USAGE
|
|
====================
|
|
|
|
A client would issue an operation by:
|
|
|
|
(1) An RxRPC socket is set up by:
|
|
|
|
client = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
|
|
|
|
Where the third parameter indicates the protocol family of the transport
|
|
socket used - usually IPv4 but it can also be IPv6 [TODO].
|
|
|
|
(2) A local address can optionally be bound:
|
|
|
|
struct sockaddr_rxrpc srx = {
|
|
.srx_family = AF_RXRPC,
|
|
.srx_service = 0, /* we're a client */
|
|
.transport_type = SOCK_DGRAM, /* type of transport socket */
|
|
.transport.sin_family = AF_INET,
|
|
.transport.sin_port = htons(7000), /* AFS callback */
|
|
.transport.sin_address = 0, /* all local interfaces */
|
|
};
|
|
bind(client, &srx, sizeof(srx));
|
|
|
|
This specifies the local UDP port to be used. If not given, a random
|
|
non-privileged port will be used. A UDP port may be shared between
|
|
several unrelated RxRPC sockets. Security is handled on a basis of
|
|
per-RxRPC virtual connection.
|
|
|
|
(3) The security is set:
|
|
|
|
const char *key = "AFS:cambridge.redhat.com";
|
|
setsockopt(client, SOL_RXRPC, RXRPC_SECURITY_KEY, key, strlen(key));
|
|
|
|
This issues a request_key() to get the key representing the security
|
|
context. The minimum security level can be set:
|
|
|
|
unsigned int sec = RXRPC_SECURITY_ENCRYPTED;
|
|
setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
|
|
&sec, sizeof(sec));
|
|
|
|
(4) The server to be contacted can then be specified (alternatively this can
|
|
be done through sendmsg):
|
|
|
|
struct sockaddr_rxrpc srx = {
|
|
.srx_family = AF_RXRPC,
|
|
.srx_service = VL_SERVICE_ID,
|
|
.transport_type = SOCK_DGRAM, /* type of transport socket */
|
|
.transport.sin_family = AF_INET,
|
|
.transport.sin_port = htons(7005), /* AFS volume manager */
|
|
.transport.sin_address = ...,
|
|
};
|
|
connect(client, &srx, sizeof(srx));
|
|
|
|
(5) The request data should then be posted to the server socket using a series
|
|
of sendmsg() calls, each with the following control message attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
|
|
MSG_MORE should be set in msghdr::msg_flags on all but the last part of
|
|
the request. Multiple requests may be made simultaneously.
|
|
|
|
An RXRPC_TX_LENGTH control message can also be specified on the first
|
|
sendmsg() call.
|
|
|
|
If a call is intended to go to a destination other than the default
|
|
specified through connect(), then msghdr::msg_name should be set on the
|
|
first request message of that call.
|
|
|
|
(6) The reply data will then be posted to the server socket for recvmsg() to
|
|
pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data
|
|
for a particular call to be read. MSG_EOR will be set on the terminal
|
|
read for a call.
|
|
|
|
All data will be delivered with the following control message attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
|
|
If an abort or error occurred, this will be returned in the control data
|
|
buffer instead, and MSG_EOR will be flagged to indicate the end of that
|
|
call.
|
|
|
|
A client may ask for a service ID it knows and ask that this be upgraded to a
|
|
better service if one is available by supplying RXRPC_UPGRADE_SERVICE on the
|
|
first sendmsg() of a call. The client should then check srx_service in the
|
|
msg_name filled in by recvmsg() when collecting the result. srx_service will
|
|
hold the same value as given to sendmsg() if the upgrade request was ignored by
|
|
the service - otherwise it will be altered to indicate the service ID the
|
|
server upgraded to. Note that the upgraded service ID is chosen by the server.
|
|
The caller has to wait until it sees the service ID in the reply before sending
|
|
any more calls (further calls to the same destination will be blocked until the
|
|
probe is concluded).
|
|
|
|
|
|
====================
|
|
EXAMPLE SERVER USAGE
|
|
====================
|
|
|
|
A server would be set up to accept operations in the following manner:
|
|
|
|
(1) An RxRPC socket is created by:
|
|
|
|
server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
|
|
|
|
Where the third parameter indicates the address type of the transport
|
|
socket used - usually IPv4.
|
|
|
|
(2) Security is set up if desired by giving the socket a keyring with server
|
|
secret keys in it:
|
|
|
|
keyring = add_key("keyring", "AFSkeys", NULL, 0,
|
|
KEY_SPEC_PROCESS_KEYRING);
|
|
|
|
const char secret_key[8] = {
|
|
0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 };
|
|
add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
|
|
|
|
setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7);
|
|
|
|
The keyring can be manipulated after it has been given to the socket. This
|
|
permits the server to add more keys, replace keys, etc. while it is live.
|
|
|
|
(3) A local address must then be bound:
|
|
|
|
struct sockaddr_rxrpc srx = {
|
|
.srx_family = AF_RXRPC,
|
|
.srx_service = VL_SERVICE_ID, /* RxRPC service ID */
|
|
.transport_type = SOCK_DGRAM, /* type of transport socket */
|
|
.transport.sin_family = AF_INET,
|
|
.transport.sin_port = htons(7000), /* AFS callback */
|
|
.transport.sin_address = 0, /* all local interfaces */
|
|
};
|
|
bind(server, &srx, sizeof(srx));
|
|
|
|
More than one service ID may be bound to a socket, provided the transport
|
|
parameters are the same. The limit is currently two. To do this, bind()
|
|
should be called twice.
|
|
|
|
(4) If service upgrading is required, first two service IDs must have been
|
|
bound and then the following option must be set:
|
|
|
|
unsigned short service_ids[2] = { from_ID, to_ID };
|
|
setsockopt(server, SOL_RXRPC, RXRPC_UPGRADEABLE_SERVICE,
|
|
service_ids, sizeof(service_ids));
|
|
|
|
This will automatically upgrade connections on service from_ID to service
|
|
to_ID if they request it. This will be reflected in msg_name obtained
|
|
through recvmsg() when the request data is delivered to userspace.
|
|
|
|
(5) The server is then set to listen out for incoming calls:
|
|
|
|
listen(server, 100);
|
|
|
|
(6) The kernel notifies the server of pending incoming connections by sending
|
|
it a message for each. This is received with recvmsg() on the server
|
|
socket. It has no data, and has a single dataless control message
|
|
attached:
|
|
|
|
RXRPC_NEW_CALL
|
|
|
|
The address that can be passed back by recvmsg() at this point should be
|
|
ignored since the call for which the message was posted may have gone by
|
|
the time it is accepted - in which case the first call still on the queue
|
|
will be accepted.
|
|
|
|
(7) The server then accepts the new call by issuing a sendmsg() with two
|
|
pieces of control data and no actual data:
|
|
|
|
RXRPC_ACCEPT - indicate connection acceptance
|
|
RXRPC_USER_CALL_ID - specify user ID for this call
|
|
|
|
(8) The first request data packet will then be posted to the server socket for
|
|
recvmsg() to pick up. At that point, the RxRPC address for the call can
|
|
be read from the address fields in the msghdr struct.
|
|
|
|
Subsequent request data will be posted to the server socket for recvmsg()
|
|
to collect as it arrives. All but the last piece of the request data will
|
|
be delivered with MSG_MORE flagged.
|
|
|
|
All data will be delivered with the following control message attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
|
|
(9) The reply data should then be posted to the server socket using a series
|
|
of sendmsg() calls, each with the following control messages attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
|
|
MSG_MORE should be set in msghdr::msg_flags on all but the last message
|
|
for a particular call.
|
|
|
|
(10) The final ACK from the client will be posted for retrieval by recvmsg()
|
|
when it is received. It will take the form of a dataless message with two
|
|
control messages attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
RXRPC_ACK - indicates final ACK (no data)
|
|
|
|
MSG_EOR will be flagged to indicate that this is the final message for
|
|
this call.
|
|
|
|
(11) Up to the point the final packet of reply data is sent, the call can be
|
|
aborted by calling sendmsg() with a dataless message with the following
|
|
control messages attached:
|
|
|
|
RXRPC_USER_CALL_ID - specifies the user ID for this call
|
|
RXRPC_ABORT - indicates abort code (4 byte data)
|
|
|
|
Any packets waiting in the socket's receive queue will be discarded if
|
|
this is issued.
|
|
|
|
Note that all the communications for a particular service take place through
|
|
the one server socket, using control messages on sendmsg() and recvmsg() to
|
|
determine the call affected.
|
|
|
|
|
|
=========================
|
|
AF_RXRPC KERNEL INTERFACE
|
|
=========================
|
|
|
|
The AF_RXRPC module also provides an interface for use by in-kernel utilities
|
|
such as the AFS filesystem. This permits such a utility to:
|
|
|
|
(1) Use different keys directly on individual client calls on one socket
|
|
rather than having to open a whole slew of sockets, one for each key it
|
|
might want to use.
|
|
|
|
(2) Avoid having RxRPC call request_key() at the point of issue of a call or
|
|
opening of a socket. Instead the utility is responsible for requesting a
|
|
key at the appropriate point. AFS, for instance, would do this during VFS
|
|
operations such as open() or unlink(). The key is then handed through
|
|
when the call is initiated.
|
|
|
|
(3) Request the use of something other than GFP_KERNEL to allocate memory.
|
|
|
|
(4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be
|
|
intercepted before they get put into the socket Rx queue and the socket
|
|
buffers manipulated directly.
|
|
|
|
To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,
|
|
bind an address as appropriate and listen if it's to be a server socket, but
|
|
then it passes this to the kernel interface functions.
|
|
|
|
The kernel interface functions are as follows:
|
|
|
|
(*) Begin a new client call.
|
|
|
|
struct rxrpc_call *
|
|
rxrpc_kernel_begin_call(struct socket *sock,
|
|
struct sockaddr_rxrpc *srx,
|
|
struct key *key,
|
|
unsigned long user_call_ID,
|
|
s64 tx_total_len,
|
|
gfp_t gfp,
|
|
rxrpc_notify_rx_t notify_rx,
|
|
bool upgrade,
|
|
bool intr,
|
|
unsigned int debug_id);
|
|
|
|
This allocates the infrastructure to make a new RxRPC call and assigns
|
|
call and connection numbers. The call will be made on the UDP port that
|
|
the socket is bound to. The call will go to the destination address of a
|
|
connected client socket unless an alternative is supplied (srx is
|
|
non-NULL).
|
|
|
|
If a key is supplied then this will be used to secure the call instead of
|
|
the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls
|
|
secured in this way will still share connections if at all possible.
|
|
|
|
The user_call_ID is equivalent to that supplied to sendmsg() in the
|
|
control data buffer. It is entirely feasible to use this to point to a
|
|
kernel data structure.
|
|
|
|
tx_total_len is the amount of data the caller is intending to transmit
|
|
with this call (or -1 if unknown at this point). Setting the data size
|
|
allows the kernel to encrypt directly to the packet buffers, thereby
|
|
saving a copy. The value may not be less than -1.
|
|
|
|
notify_rx is a pointer to a function to be called when events such as
|
|
incoming data packets or remote aborts happen.
|
|
|
|
upgrade should be set to true if a client operation should request that
|
|
the server upgrade the service to a better one. The resultant service ID
|
|
is returned by rxrpc_kernel_recv_data().
|
|
|
|
intr should be set to true if the call should be interruptible. If this
|
|
is not set, this function may not return until a channel has been
|
|
allocated; if it is set, the function may return -ERESTARTSYS.
|
|
|
|
debug_id is the call debugging ID to be used for tracing. This can be
|
|
obtained by atomically incrementing rxrpc_debug_id.
|
|
|
|
If this function is successful, an opaque reference to the RxRPC call is
|
|
returned. The caller now holds a reference on this and it must be
|
|
properly ended.
|
|
|
|
(*) End a client call.
|
|
|
|
void rxrpc_kernel_end_call(struct socket *sock,
|
|
struct rxrpc_call *call);
|
|
|
|
This is used to end a previously begun call. The user_call_ID is expunged
|
|
from AF_RXRPC's knowledge and will not be seen again in association with
|
|
the specified call.
|
|
|
|
(*) Send data through a call.
|
|
|
|
typedef void (*rxrpc_notify_end_tx_t)(struct sock *sk,
|
|
unsigned long user_call_ID,
|
|
struct sk_buff *skb);
|
|
|
|
int rxrpc_kernel_send_data(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
struct msghdr *msg,
|
|
size_t len,
|
|
rxrpc_notify_end_tx_t notify_end_rx);
|
|
|
|
This is used to supply either the request part of a client call or the
|
|
reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the
|
|
data buffers to be used. msg_iov may not be NULL and must point
|
|
exclusively to in-kernel virtual addresses. msg.msg_flags may be given
|
|
MSG_MORE if there will be subsequent data sends for this call.
|
|
|
|
The msg must not specify a destination address, control data or any flags
|
|
other than MSG_MORE. len is the total amount of data to transmit.
|
|
|
|
notify_end_rx can be NULL or it can be used to specify a function to be
|
|
called when the call changes state to end the Tx phase. This function is
|
|
called with the call-state spinlock held to prevent any reply or final ACK
|
|
from being delivered first.
|
|
|
|
(*) Receive data from a call.
|
|
|
|
int rxrpc_kernel_recv_data(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
void *buf,
|
|
size_t size,
|
|
size_t *_offset,
|
|
bool want_more,
|
|
u32 *_abort,
|
|
u16 *_service)
|
|
|
|
This is used to receive data from either the reply part of a client call
|
|
or the request part of a service call. buf and size specify how much
|
|
data is desired and where to store it. *_offset is added on to buf and
|
|
subtracted from size internally; the amount copied into the buffer is
|
|
added to *_offset before returning.
|
|
|
|
want_more should be true if further data will be required after this is
|
|
satisfied and false if this is the last item of the receive phase.
|
|
|
|
There are three normal returns: 0 if the buffer was filled and want_more
|
|
was true; 1 if the buffer was filled, the last DATA packet has been
|
|
emptied and want_more was false; and -EAGAIN if the function needs to be
|
|
called again.
|
|
|
|
If the last DATA packet is processed but the buffer contains less than
|
|
the amount requested, EBADMSG is returned. If want_more wasn't set, but
|
|
more data was available, EMSGSIZE is returned.
|
|
|
|
If a remote ABORT is detected, the abort code received will be stored in
|
|
*_abort and ECONNABORTED will be returned.
|
|
|
|
The service ID that the call ended up with is returned into *_service.
|
|
This can be used to see if a call got a service upgrade.
|
|
|
|
(*) Abort a call.
|
|
|
|
void rxrpc_kernel_abort_call(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
u32 abort_code);
|
|
|
|
This is used to abort a call if it's still in an abortable state. The
|
|
abort code specified will be placed in the ABORT message sent.
|
|
|
|
(*) Intercept received RxRPC messages.
|
|
|
|
typedef void (*rxrpc_interceptor_t)(struct sock *sk,
|
|
unsigned long user_call_ID,
|
|
struct sk_buff *skb);
|
|
|
|
void
|
|
rxrpc_kernel_intercept_rx_messages(struct socket *sock,
|
|
rxrpc_interceptor_t interceptor);
|
|
|
|
This installs an interceptor function on the specified AF_RXRPC socket.
|
|
All messages that would otherwise wind up in the socket's Rx queue are
|
|
then diverted to this function. Note that care must be taken to process
|
|
the messages in the right order to maintain DATA message sequentiality.
|
|
|
|
The interceptor function itself is provided with the address of the socket
|
|
and handling the incoming message, the ID assigned by the kernel utility
|
|
to the call and the socket buffer containing the message.
|
|
|
|
The skb->mark field indicates the type of message:
|
|
|
|
MARK MEANING
|
|
=============================== =======================================
|
|
RXRPC_SKB_MARK_DATA Data message
|
|
RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call
|
|
RXRPC_SKB_MARK_BUSY Client call rejected as server busy
|
|
RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer
|
|
RXRPC_SKB_MARK_NET_ERROR Network error detected
|
|
RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered
|
|
RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance
|
|
|
|
The remote abort message can be probed with rxrpc_kernel_get_abort_code().
|
|
The two error messages can be probed with rxrpc_kernel_get_error_number().
|
|
A new call can be accepted with rxrpc_kernel_accept_call().
|
|
|
|
Data messages can have their contents extracted with the usual bunch of
|
|
socket buffer manipulation functions. A data message can be determined to
|
|
be the last one in a sequence with rxrpc_kernel_is_data_last(). When a
|
|
data message has been used up, rxrpc_kernel_data_consumed() should be
|
|
called on it.
|
|
|
|
Messages should be handled to rxrpc_kernel_free_skb() to dispose of. It
|
|
is possible to get extra refs on all types of message for later freeing,
|
|
but this may pin the state of a call until the message is finally freed.
|
|
|
|
(*) Accept an incoming call.
|
|
|
|
struct rxrpc_call *
|
|
rxrpc_kernel_accept_call(struct socket *sock,
|
|
unsigned long user_call_ID);
|
|
|
|
This is used to accept an incoming call and to assign it a call ID. This
|
|
function is similar to rxrpc_kernel_begin_call() and calls accepted must
|
|
be ended in the same way.
|
|
|
|
If this function is successful, an opaque reference to the RxRPC call is
|
|
returned. The caller now holds a reference on this and it must be
|
|
properly ended.
|
|
|
|
(*) Reject an incoming call.
|
|
|
|
int rxrpc_kernel_reject_call(struct socket *sock);
|
|
|
|
This is used to reject the first incoming call on the socket's queue with
|
|
a BUSY message. -ENODATA is returned if there were no incoming calls.
|
|
Other errors may be returned if the call had been aborted (-ECONNABORTED)
|
|
or had timed out (-ETIME).
|
|
|
|
(*) Allocate a null key for doing anonymous security.
|
|
|
|
struct key *rxrpc_get_null_key(const char *keyname);
|
|
|
|
This is used to allocate a null RxRPC key that can be used to indicate
|
|
anonymous security for a particular domain.
|
|
|
|
(*) Get the peer address of a call.
|
|
|
|
void rxrpc_kernel_get_peer(struct socket *sock, struct rxrpc_call *call,
|
|
struct sockaddr_rxrpc *_srx);
|
|
|
|
This is used to find the remote peer address of a call.
|
|
|
|
(*) Set the total transmit data size on a call.
|
|
|
|
void rxrpc_kernel_set_tx_length(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
s64 tx_total_len);
|
|
|
|
This sets the amount of data that the caller is intending to transmit on a
|
|
call. It's intended to be used for setting the reply size as the request
|
|
size should be set when the call is begun. tx_total_len may not be less
|
|
than zero.
|
|
|
|
(*) Get call RTT.
|
|
|
|
u64 rxrpc_kernel_get_rtt(struct socket *sock, struct rxrpc_call *call);
|
|
|
|
Get the RTT time to the peer in use by a call. The value returned is in
|
|
nanoseconds.
|
|
|
|
(*) Check call still alive.
|
|
|
|
bool rxrpc_kernel_check_life(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
u32 *_life);
|
|
void rxrpc_kernel_probe_life(struct socket *sock,
|
|
struct rxrpc_call *call);
|
|
|
|
The first function passes back in *_life a number that is updated when
|
|
ACKs are received from the peer (notably including PING RESPONSE ACKs
|
|
which we can elicit by sending PING ACKs to see if the call still exists
|
|
on the server). The caller should compare the numbers of two calls to see
|
|
if the call is still alive after waiting for a suitable interval. It also
|
|
returns true as long as the call hasn't yet reached the completed state.
|
|
|
|
This allows the caller to work out if the server is still contactable and
|
|
if the call is still alive on the server while waiting for the server to
|
|
process a client operation.
|
|
|
|
The second function causes a ping ACK to be transmitted to try to provoke
|
|
the peer into responding, which would then cause the value returned by the
|
|
first function to change. Note that this must be called in TASK_RUNNING
|
|
state.
|
|
|
|
(*) Get reply timestamp.
|
|
|
|
bool rxrpc_kernel_get_reply_time(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
ktime_t *_ts)
|
|
|
|
This allows the timestamp on the first DATA packet of the reply of a
|
|
client call to be queried, provided that it is still in the Rx ring. If
|
|
successful, the timestamp will be stored into *_ts and true will be
|
|
returned; false will be returned otherwise.
|
|
|
|
(*) Get remote client epoch.
|
|
|
|
u32 rxrpc_kernel_get_epoch(struct socket *sock,
|
|
struct rxrpc_call *call)
|
|
|
|
This allows the epoch that's contained in packets of an incoming client
|
|
call to be queried. This value is returned. The function always
|
|
successful if the call is still in progress. It shouldn't be called once
|
|
the call has expired. Note that calling this on a local client call only
|
|
returns the local epoch.
|
|
|
|
This value can be used to determine if the remote client has been
|
|
restarted as it shouldn't change otherwise.
|
|
|
|
(*) Set the maxmimum lifespan on a call.
|
|
|
|
void rxrpc_kernel_set_max_life(struct socket *sock,
|
|
struct rxrpc_call *call,
|
|
unsigned long hard_timeout)
|
|
|
|
This sets the maximum lifespan on a call to hard_timeout (which is in
|
|
jiffies). In the event of the timeout occurring, the call will be
|
|
aborted and -ETIME or -ETIMEDOUT will be returned.
|
|
|
|
|
|
=======================
|
|
CONFIGURABLE PARAMETERS
|
|
=======================
|
|
|
|
The RxRPC protocol driver has a number of configurable parameters that can be
|
|
adjusted through sysctls in /proc/net/rxrpc/:
|
|
|
|
(*) req_ack_delay
|
|
|
|
The amount of time in milliseconds after receiving a packet with the
|
|
request-ack flag set before we honour the flag and actually send the
|
|
requested ack.
|
|
|
|
Usually the other side won't stop sending packets until the advertised
|
|
reception window is full (to a maximum of 255 packets), so delaying the
|
|
ACK permits several packets to be ACK'd in one go.
|
|
|
|
(*) soft_ack_delay
|
|
|
|
The amount of time in milliseconds after receiving a new packet before we
|
|
generate a soft-ACK to tell the sender that it doesn't need to resend.
|
|
|
|
(*) idle_ack_delay
|
|
|
|
The amount of time in milliseconds after all the packets currently in the
|
|
received queue have been consumed before we generate a hard-ACK to tell
|
|
the sender it can free its buffers, assuming no other reason occurs that
|
|
we would send an ACK.
|
|
|
|
(*) resend_timeout
|
|
|
|
The amount of time in milliseconds after transmitting a packet before we
|
|
transmit it again, assuming no ACK is received from the receiver telling
|
|
us they got it.
|
|
|
|
(*) max_call_lifetime
|
|
|
|
The maximum amount of time in seconds that a call may be in progress
|
|
before we preemptively kill it.
|
|
|
|
(*) dead_call_expiry
|
|
|
|
The amount of time in seconds before we remove a dead call from the call
|
|
list. Dead calls are kept around for a little while for the purpose of
|
|
repeating ACK and ABORT packets.
|
|
|
|
(*) connection_expiry
|
|
|
|
The amount of time in seconds after a connection was last used before we
|
|
remove it from the connection list. While a connection is in existence,
|
|
it serves as a placeholder for negotiated security; when it is deleted,
|
|
the security must be renegotiated.
|
|
|
|
(*) transport_expiry
|
|
|
|
The amount of time in seconds after a transport was last used before we
|
|
remove it from the transport list. While a transport is in existence, it
|
|
serves to anchor the peer data and keeps the connection ID counter.
|
|
|
|
(*) rxrpc_rx_window_size
|
|
|
|
The size of the receive window in packets. This is the maximum number of
|
|
unconsumed received packets we're willing to hold in memory for any
|
|
particular call.
|
|
|
|
(*) rxrpc_rx_mtu
|
|
|
|
The maximum packet MTU size that we're willing to receive in bytes. This
|
|
indicates to the peer whether we're willing to accept jumbo packets.
|
|
|
|
(*) rxrpc_rx_jumbo_max
|
|
|
|
The maximum number of packets that we're willing to accept in a jumbo
|
|
packet. Non-terminal packets in a jumbo packet must contain a four byte
|
|
header plus exactly 1412 bytes of data. The terminal packet must contain
|
|
a four byte header plus any amount of data. In any event, a jumbo packet
|
|
may not exceed rxrpc_rx_mtu in size.
|