mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-24 04:34:08 +08:00
21457f4a91
Remove rxrpc_get_reply_time() as that is no longer used now that the call issue time is used instead of the reply time. Signed-off-by: David Howells <dhowells@redhat.com>
1168 lines
45 KiB
ReStructuredText
1168 lines
45 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
======================
|
|
RxRPC Network Protocol
|
|
======================
|
|
|
|
The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
|
|
that can be used to perform RxRPC remote operations. This is done over sockets
|
|
of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and
|
|
receive data, aborts and errors.
|
|
|
|
Contents of this document:
|
|
|
|
(#) Overview.
|
|
|
|
(#) RxRPC protocol summary.
|
|
|
|
(#) AF_RXRPC driver model.
|
|
|
|
(#) Control messages.
|
|
|
|
(#) Socket options.
|
|
|
|
(#) Security.
|
|
|
|
(#) Example client usage.
|
|
|
|
(#) Example server usage.
|
|
|
|
(#) AF_RXRPC kernel interface.
|
|
|
|
(#) Configurable parameters.
|
|
|
|
|
|
Overview
|
|
========
|
|
|
|
RxRPC is a two-layer protocol. There is a session layer which provides
|
|
reliable virtual connections using UDP over IPv4 (or IPv6) as the transport
|
|
layer, but implements a real network protocol; and there's the presentation
|
|
layer which renders structured data to binary blobs and back again using XDR
|
|
(as does SunRPC)::
|
|
|
|
+-------------+
|
|
| Application |
|
|
+-------------+
|
|
| XDR | Presentation
|
|
+-------------+
|
|
| RxRPC | Session
|
|
+-------------+
|
|
| UDP | Transport
|
|
+-------------+
|
|
|
|
|
|
AF_RXRPC provides:
|
|
|
|
(1) Part of an RxRPC facility for both kernel and userspace applications by
|
|
making the session part of it a Linux network protocol (AF_RXRPC).
|
|
|
|
(2) A two-phase protocol. The client transmits a blob (the request) and then
|
|
receives a blob (the reply), and the server receives the request and then
|
|
transmits the reply.
|
|
|
|
(3) Retention of the reusable bits of the transport system set up for one call
|
|
to speed up subsequent calls.
|
|
|
|
(4) A secure protocol, using the Linux kernel's key retention facility to
|
|
manage security on the client end. The server end must of necessity be
|
|
more active in security negotiations.
|
|
|
|
AF_RXRPC does not provide XDR marshalling/presentation facilities. That is
|
|
left to the application. AF_RXRPC only deals in blobs. Even the operation ID
|
|
is just the first four bytes of the request blob, and as such is beyond the
|
|
kernel's interest.
|
|
|
|
|
|
Sockets of AF_RXRPC family are:
|
|
|
|
(1) created as type SOCK_DGRAM;
|
|
|
|
(2) provided with a protocol of the type of underlying transport they're going
|
|
to use - currently only PF_INET is supported.
|
|
|
|
|
|
The Andrew File System (AFS) is an example of an application that uses this and
|
|
that has both kernel (filesystem) and userspace (utility) components.
|
|
|
|
|
|
RxRPC Protocol Summary
|
|
======================
|
|
|
|
An overview of the RxRPC protocol:
|
|
|
|
(#) RxRPC sits on top of another networking protocol (UDP is the only option
|
|
currently), and uses this to provide network transport. UDP ports, for
|
|
example, provide transport endpoints.
|
|
|
|
(#) RxRPC supports multiple virtual "connections" from any given transport
|
|
endpoint, thus allowing the endpoints to be shared, even to the same
|
|
remote endpoint.
|
|
|
|
(#) Each connection goes to a particular "service". A connection may not go
|
|
to multiple services. A service may be considered the RxRPC equivalent of
|
|
a port number. AF_RXRPC permits multiple services to share an endpoint.
|
|
|
|
(#) Client-originating packets are marked, thus a transport endpoint can be
|
|
shared between client and server connections (connections have a
|
|
direction).
|
|
|
|
(#) Up to a billion connections may be supported concurrently between one
|
|
local transport endpoint and one service on one remote endpoint. An RxRPC
|
|
connection is described by seven numbers::
|
|
|
|
Local address }
|
|
Local port } Transport (UDP) address
|
|
Remote address }
|
|
Remote port }
|
|
Direction
|
|
Connection ID
|
|
Service ID
|
|
|
|
(#) Each RxRPC operation is a "call". A connection may make up to four
|
|
billion calls, but only up to four calls may be in progress on a
|
|
connection at any one time.
|
|
|
|
(#) Calls are two-phase and asymmetric: the client sends its request data,
|
|
which the service receives; then the service transmits the reply data
|
|
which the client receives.
|
|
|
|
(#) The data blobs are of indefinite size, the end of a phase is marked with a
|
|
flag in the packet. The number of packets of data making up one blob may
|
|
not exceed 4 billion, however, as this would cause the sequence number to
|
|
wrap.
|
|
|
|
(#) The first four bytes of the request data are the service operation ID.
|
|
|
|
(#) Security is negotiated on a per-connection basis. The connection is
|
|
initiated by the first data packet on it arriving. If security is
|
|
requested, the server then issues a "challenge" and then the client
|
|
replies with a "response". If the response is successful, the security is
|
|
set for the lifetime of that connection, and all subsequent calls made
|
|
upon it use that same security. In the event that the server lets a
|
|
connection lapse before the client, the security will be renegotiated if
|
|
the client uses the connection again.
|
|
|
|
(#) Calls use ACK packets to handle reliability. Data packets are also
|
|
explicitly sequenced per call.
|
|
|
|
(#) There are two types of positive acknowledgment: hard-ACKs and soft-ACKs.
|
|
A hard-ACK indicates to the far side that all the data received to a point
|
|
has been received and processed; a soft-ACK indicates that the data has
|
|
been received but may yet be discarded and re-requested. The sender may
|
|
not discard any transmittable packets until they've been hard-ACK'd.
|
|
|
|
(#) Reception of a reply data packet implicitly hard-ACK's all the data
|
|
packets that make up the request.
|
|
|
|
(#) An call is complete when the request has been sent, the reply has been
|
|
received and the final hard-ACK on the last packet of the reply has
|
|
reached the server.
|
|
|
|
(#) An call may be aborted by either end at any time up to its completion.
|
|
|
|
|
|
AF_RXRPC Driver Model
|
|
=====================
|
|
|
|
About the AF_RXRPC driver:
|
|
|
|
(#) The AF_RXRPC protocol transparently uses internal sockets of the transport
|
|
protocol to represent transport endpoints.
|
|
|
|
(#) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC
|
|
connections are handled transparently. One client socket may be used to
|
|
make multiple simultaneous calls to the same service. One server socket
|
|
may handle calls from many clients.
|
|
|
|
(#) Additional parallel client connections will be initiated to support extra
|
|
concurrent calls, up to a tunable limit.
|
|
|
|
(#) Each connection is retained for a certain amount of time [tunable] after
|
|
the last call currently using it has completed in case a new call is made
|
|
that could reuse it.
|
|
|
|
(#) Each internal UDP socket is retained [tunable] for a certain amount of
|
|
time [tunable] after the last connection using it discarded, in case a new
|
|
connection is made that could use it.
|
|
|
|
(#) A client-side connection is only shared between calls if they have
|
|
the same key struct describing their security (and assuming the calls
|
|
would otherwise share the connection). Non-secured calls would also be
|
|
able to share connections with each other.
|
|
|
|
(#) A server-side connection is shared if the client says it is.
|
|
|
|
(#) ACK'ing is handled by the protocol driver automatically, including ping
|
|
replying.
|
|
|
|
(#) SO_KEEPALIVE automatically pings the other side to keep the connection
|
|
alive [TODO].
|
|
|
|
(#) If an ICMP error is received, all calls affected by that error will be
|
|
aborted with an appropriate network error passed through recvmsg().
|
|
|
|
|
|
Interaction with the user of the RxRPC socket:
|
|
|
|
(#) A socket is made into a server socket by binding an address with a
|
|
non-zero service ID.
|
|
|
|
(#) In the client, sending a request is achieved with one or more sendmsgs,
|
|
followed by the reply being received with one or more recvmsgs.
|
|
|
|
(#) The first sendmsg for a request to be sent from a client contains a tag to
|
|
be used in all other sendmsgs or recvmsgs associated with that call. The
|
|
tag is carried in the control data.
|
|
|
|
(#) connect() is used to supply a default destination address for a client
|
|
socket. This may be overridden by supplying an alternate address to the
|
|
first sendmsg() of a call (struct msghdr::msg_name).
|
|
|
|
(#) If connect() is called on an unbound client, a random local port will
|
|
bound before the operation takes place.
|
|
|
|
(#) A server socket may also be used to make client calls. To do this, the
|
|
first sendmsg() of the call must specify the target address. The server's
|
|
transport endpoint is used to send the packets.
|
|
|
|
(#) Once the application has received the last message associated with a call,
|
|
the tag is guaranteed not to be seen again, and so it can be used to pin
|
|
client resources. A new call can then be initiated with the same tag
|
|
without fear of interference.
|
|
|
|
(#) In the server, a request is received with one or more recvmsgs, then the
|
|
the reply is transmitted with one or more sendmsgs, and then the final ACK
|
|
is received with a last recvmsg.
|
|
|
|
(#) When sending data for a call, sendmsg is given MSG_MORE if there's more
|
|
data to come on that call.
|
|
|
|
(#) When receiving data for a call, recvmsg flags MSG_MORE if there's more
|
|
data to come for that call.
|
|
|
|
(#) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg
|
|
to indicate the terminal message for that call.
|
|
|
|
(#) A call may be aborted by adding an abort control message to the control
|
|
data. Issuing an abort terminates the kernel's use of that call's tag.
|
|
Any messages waiting in the receive queue for that call will be discarded.
|
|
|
|
(#) Aborts, busy notifications and challenge packets are delivered by recvmsg,
|
|
and control data messages will be set to indicate the context. Receiving
|
|
an abort or a busy message terminates the kernel's use of that call's tag.
|
|
|
|
(#) The control data part of the msghdr struct is used for a number of things:
|
|
|
|
(#) The tag of the intended or affected call.
|
|
|
|
(#) Sending or receiving errors, aborts and busy notifications.
|
|
|
|
(#) Notifications of incoming calls.
|
|
|
|
(#) Sending debug requests and receiving debug replies [TODO].
|
|
|
|
(#) When the kernel has received and set up an incoming call, it sends a
|
|
message to server application to let it know there's a new call awaiting
|
|
its acceptance [recvmsg reports a special control message]. The server
|
|
application then uses sendmsg to assign a tag to the new call. Once that
|
|
is done, the first part of the request data will be delivered by recvmsg.
|
|
|
|
(#) The server application has to provide the server socket with a keyring of
|
|
secret keys corresponding to the security types it permits. When a secure
|
|
connection is being set up, the kernel looks up the appropriate secret key
|
|
in the keyring and then sends a challenge packet to the client and
|
|
receives a response packet. The kernel then checks the authorisation of
|
|
the packet and either aborts the connection or sets up the security.
|
|
|
|
(#) The name of the key a client will use to secure its communications is
|
|
nominated by a socket option.
|
|
|
|
|
|
Notes on sendmsg:
|
|
|
|
(#) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is
|
|
making progress at accepting packets within a reasonable time such that we
|
|
manage to queue up all the data for transmission. This requires the
|
|
client to accept at least one packet per 2*RTT time period.
|
|
|
|
If this isn't set, sendmsg() will return immediately, either returning
|
|
EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data
|
|
consumed.
|
|
|
|
|
|
Notes on recvmsg:
|
|
|
|
(#) If there's a sequence of data messages belonging to a particular call on
|
|
the receive queue, then recvmsg will keep working through them until:
|
|
|
|
(a) it meets the end of that call's received data,
|
|
|
|
(b) it meets a non-data message,
|
|
|
|
(c) it meets a message belonging to a different call, or
|
|
|
|
(d) it fills the user buffer.
|
|
|
|
If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
|
|
reception of further data, until one of the above four conditions is met.
|
|
|
|
(2) MSG_PEEK operates similarly, but will return immediately if it has put any
|
|
data in the buffer rather than sleeping until it can fill the buffer.
|
|
|
|
(3) If a data message is only partially consumed in filling a user buffer,
|
|
then the remainder of that message will be left on the front of the queue
|
|
for the next taker. MSG_TRUNC will never be flagged.
|
|
|
|
(4) If there is more data to be had on a call (it hasn't copied the last byte
|
|
of the last data message in that phase yet), then MSG_MORE will be
|
|
flagged.
|
|
|
|
|
|
Control Messages
|
|
================
|
|
|
|
AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
|
|
calls, to invoke certain actions and to report certain conditions. These are:
|
|
|
|
======================= === =========== ===============================
|
|
MESSAGE ID SRT DATA MEANING
|
|
======================= === =========== ===============================
|
|
RXRPC_USER_CALL_ID sr- User ID App's call specifier
|
|
RXRPC_ABORT srt Abort code Abort code to issue/received
|
|
RXRPC_ACK -rt n/a Final ACK received
|
|
RXRPC_NET_ERROR -rt error num Network error on call
|
|
RXRPC_BUSY -rt n/a Call rejected (server busy)
|
|
RXRPC_LOCAL_ERROR -rt error num Local error encountered
|
|
RXRPC_NEW_CALL -r- n/a New call received
|
|
RXRPC_ACCEPT s-- n/a Accept new call
|
|
RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call
|
|
RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded
|
|
RXRPC_TX_LENGTH s-- data len Total length of Tx data
|
|
======================= === =========== ===============================
|
|
|
|
(SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
|
|
|
|
(#) RXRPC_USER_CALL_ID
|
|
|
|
This is used to indicate the application's call ID. It's an unsigned long
|
|
that the app specifies in the client by attaching it to the first data
|
|
message or in the server by passing it in association with an RXRPC_ACCEPT
|
|
message. recvmsg() passes it in conjunction with all messages except
|
|
those of the RXRPC_NEW_CALL message.
|
|
|
|
(#) RXRPC_ABORT
|
|
|
|
This is can be used by an application to abort a call by passing it to
|
|
sendmsg, or it can be delivered by recvmsg to indicate a remote abort was
|
|
received. Either way, it must be associated with an RXRPC_USER_CALL_ID to
|
|
specify the call affected. If an abort is being sent, then error EBADSLT
|
|
will be returned if there is no call with that user ID.
|
|
|
|
(#) RXRPC_ACK
|
|
|
|
This is delivered to a server application to indicate that the final ACK
|
|
of a call was received from the client. It will be associated with an
|
|
RXRPC_USER_CALL_ID to indicate the call that's now complete.
|
|
|
|
(#) RXRPC_NET_ERROR
|
|
|
|
This is delivered to an application to indicate that an ICMP error message
|
|
was encountered in the process of trying to talk to the peer. An
|
|
errno-class integer value will be included in the control message data
|
|
indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
|
|
affected.
|
|
|
|
(#) RXRPC_BUSY
|
|
|
|
This is delivered to a client application to indicate that a call was
|
|
rejected by the server due to the server being busy. It will be
|
|
associated with an RXRPC_USER_CALL_ID to indicate the rejected call.
|
|
|
|
(#) RXRPC_LOCAL_ERROR
|
|
|
|
This is delivered to an application to indicate that a local error was
|
|
encountered and that a call has been aborted because of it. An
|
|
errno-class integer value will be included in the control message data
|
|
indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
|
|
affected.
|
|
|
|
(#) RXRPC_NEW_CALL
|
|
|
|
This is delivered to indicate to a server application that a new call has
|
|
arrived and is awaiting acceptance. No user ID is associated with this,
|
|
as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT.
|
|
|
|
(#) RXRPC_ACCEPT
|
|
|
|
This is used by a server application to attempt to accept a call and
|
|
assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID
|
|
to indicate the user ID to be assigned. If there is no call to be
|
|
accepted (it may have timed out, been aborted, etc.), then sendmsg will
|
|
return error ENODATA. If the user ID is already in use by another call,
|
|
then error EBADSLT will be returned.
|
|
|
|
(#) RXRPC_EXCLUSIVE_CALL
|
|
|
|
This is used to indicate that a client call should be made on a one-off
|
|
connection. The connection is discarded once the call has terminated.
|
|
|
|
(#) RXRPC_UPGRADE_SERVICE
|
|
|
|
This is used to make a client call to probe if the specified service ID
|
|
may be upgraded by the server. The caller must check msg_name returned to
|
|
recvmsg() for the service ID actually in use. The operation probed must
|
|
be one that takes the same arguments in both services.
|
|
|
|
Once this has been used to establish the upgrade capability (or lack
|
|
thereof) of the server, the service ID returned should be used for all
|
|
future communication to that server and RXRPC_UPGRADE_SERVICE should no
|
|
longer be set.
|
|
|
|
(#) RXRPC_TX_LENGTH
|
|
|
|
This is used to inform the kernel of the total amount of data that is
|
|
going to be transmitted by a call (whether in a client request or a
|
|
service response). If given, it allows the kernel to encrypt from the
|
|
userspace buffer directly to the packet buffers, rather than copying into
|
|
the buffer and then encrypting in place. This may only be given with the
|
|
first sendmsg() providing data for a call. EMSGSIZE will be generated if
|
|
the amount of data actually given is different.
|
|
|
|
This takes a parameter of __s64 type that indicates how much will be
|
|
transmitted. This may not be less than zero.
|
|
|
|
The symbol RXRPC__SUPPORTED is defined as one more than the highest control
|
|
message type supported. At run time this can be queried by means of the
|
|
RXRPC_SUPPORTED_CMSG socket option (see below).
|
|
|
|
|
|
==============
|
|
SOCKET OPTIONS
|
|
==============
|
|
|
|
AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:
|
|
|
|
(#) RXRPC_SECURITY_KEY
|
|
|
|
This is used to specify the description of the key to be used. The key is
|
|
extracted from the calling process's keyrings with request_key() and
|
|
should be of "rxrpc" type.
|
|
|
|
The optval pointer points to the description string, and optlen indicates
|
|
how long the string is, without the NUL terminator.
|
|
|
|
(#) RXRPC_SECURITY_KEYRING
|
|
|
|
Similar to above but specifies a keyring of server secret keys to use (key
|
|
type "keyring"). See the "Security" section.
|
|
|
|
(#) RXRPC_EXCLUSIVE_CONNECTION
|
|
|
|
This is used to request that new connections should be used for each call
|
|
made subsequently on this socket. optval should be NULL and optlen 0.
|
|
|
|
(#) RXRPC_MIN_SECURITY_LEVEL
|
|
|
|
This is used to specify the minimum security level required for calls on
|
|
this socket. optval must point to an int containing one of the following
|
|
values:
|
|
|
|
(a) RXRPC_SECURITY_PLAIN
|
|
|
|
Encrypted checksum only.
|
|
|
|
(b) RXRPC_SECURITY_AUTH
|
|
|
|
Encrypted checksum plus packet padded and first eight bytes of packet
|
|
encrypted - which includes the actual packet length.
|
|
|
|
(c) RXRPC_SECURITY_ENCRYPT
|
|
|
|
Encrypted checksum plus entire packet padded and encrypted, including
|
|
actual packet length.
|
|
|
|
(#) RXRPC_UPGRADEABLE_SERVICE
|
|
|
|
This is used to indicate that a service socket with two bindings may
|
|
upgrade one bound service to the other if requested by the client. optval
|
|
must point to an array of two unsigned short ints. The first is the
|
|
service ID to upgrade from and the second the service ID to upgrade to.
|
|
|
|
(#) RXRPC_SUPPORTED_CMSG
|
|
|
|
This is a read-only option that writes an int into the buffer indicating
|
|
the highest control message type supported.
|
|
|
|
|
|
========
|
|
SECURITY
|
|
========
|
|
|
|
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_ENCRYPT;
|
|
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 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.
|
|
|
|
(#) Apply the RXRPC_MIN_SECURITY_LEVEL sockopt to a socket from within in the
|
|
kernel::
|
|
|
|
int rxrpc_sock_set_min_security_level(struct sock *sk,
|
|
unsigned int val);
|
|
|
|
This specifies the minimum security level required for calls on this
|
|
socket.
|
|
|
|
|
|
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.
|