Define l2tp_session_place_call() which can start either an incomming
or outgoing session depending on the 'sess->lns_mode' flag. This
removes the need for testing session mode before calling
l2tp_tunnel_start_session().
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Creating new sessions always involves the same steps:
  * Create new session context
  * Call session's first function in this context
  * Start session establishment timer

This patch starts centralising the first two steps in
l2tp_tunnel_confirm_session() (renamed l2tp_tunnel_start_session()
in order to use similar ways for starting tunnels and sessions).
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Handling ICRQ or OCRQ requests occurs in tunnel context, but if session
creation is rejected, a CDN has to be sent. However, l2tp_send_CDN() is
supposed to be called in session context. This means that it uselessly
switches to tunnel context before sending messages and requires a
session structure to work on.

This patch creates a new function for sending CDN from tunnel context.
It gets the session and peer session IDs from its arguments and calls
l2tp_tunnel_send() directly. The l2tp_recv_ICRQ() and l2tp_recv_OCRQ()
functions are modified to take advantage of this new function and will
now send CDN even upon early message processing error.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define the l2tp_{tunnel,session}_send() functions for sending
messages in tunnel or session context. Session messages have
their session ID automatically set and switch to tunnel context
for sending messages.

Though the 'debug' parameter is removed from function prototypes,
the logging mechanism is respected: HELLO and ZLB are displayed as
'debug' messages while other message types use 'info2'.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Print details about errors that can occur when using the
"l2tp create tunnel" command line.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Print details about errors that can occur when using the
"l2tp create session" command line.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Check for errors in start_udp_server() and return exit status to
calling function.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Use memdebug variants of {m,re}alloc() so that the corresponding
_free() will work correctly if MEMDEBUG is defined.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Update l2tp_session_free's prototype to return its error status.
Do the opposite for l2tp_tunnel_cancel_session (make it return void)
as it never fails.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define macros for logging tunnel or session messages with automatic
context information display.
Use these macros to replace most existing error messages + add
missing ones.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add entries in accel-ppp.conf.5 for configuration options defined by
the CLI module.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define the "sessions-columns" option (in the [cli] section) to let
the user select the default set of columns that will be displayed by
the "show sessions" command.
Unrecognised column names are silently discarded.

Configuration example:
    [cli]
        telnet=127.0.0.1:2000
        password=secret
        sessions-columns=ifname,ip,username
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Gracefully handle the case where no column has been selected for the
"show sessions" command. Such situation will be possible once the set
of default displayed columns will be made configurable from
accel-ppp.conf.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

When several messages are sent consecutively, the peer can reply with
a single ZLB to acknowledge all messages. In this case, removing
only the first message from the retransmission queue isn't enough
(acknowledged messages left in the queue will be retransmitted).
This case can happen when replying to an outgoing call request, wich
is handled by sending two messages in a row (an OCRP and an OCCN).

This patch avoids useless retransmissions by removing all messages
acknowledged by peer from the retransmission queue.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Handle OCRQ requests when operating as LAC.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Send the Result and Error fields of StopCCN and CDN messages in network
byte order.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Use the Assigned Tunnel ID and Result Code AVPs when handling StopCCN
messages.
The Result Code AVP is used to improve log messages, while the Assigned
Tunnel ID is used to set the tunnel's peer-tid field.

Setting peer-tid makes the ZLB to be sent to the right tunnel in case
no Assigned Tunnel ID had been received yet (this happens when the host
sends an SCCRQ but the peer directly rejects the connection with
StopCCN).
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Send a ZLB after reception of Set-Link-Info (SLI) messages to avoid
retransmissions from the LNS.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Fix a few errors in dictionary.rfc2661 and dictionary.rfc3931 (missing
entries, typos, wrong type/flags, etc.) and re-generate attr_defs.h.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add const qualifier to attributes pointers used for parsing incoming
L2TP messages.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add const qualifier to the Message Type variable used by the generic
L2TP reception functions.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add const qualifier to packet passed to l2tp_recv_*() functions.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define the address parameter of l2tp_packet_alloc() as constant.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add const qualifiers to the string used for reading configuration.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Declare parameters and variables of l2tp_packet_print() as constant.
Also update l2tp_dict_find_value() prototype to accept options passed
by l2tp_packet_print().
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Handle CLI_CMD_FAILED like other command errors (i.e. return 0 to the
caller and send a generic error message).
This makes the CLI handler to flush its input buffer, so that
processing of the next command will be made correctly. This also makes
the telnet handler to send its prompt message.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Refuse to initiate tunnel creation to peers not defined in the
"client-ip-range" configuration section.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Don't call strlen() if conf_secret is NULL.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Implement incomming call placement for tunnels operating as LAC.
A user can place incomming calls using the command line interface.
For example, the following command will place a call on tunnel 1:
  accel-ppp# l2tp create session tid 1
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Add the "l2tp create tunnel" command to initiate new tunnels.

This command accepts three parameters:
  * peer-addr (mandatory): IPv4 address of the remote tunnel end.

  * host-addr (optional): IPv4 address of the local tunnel end.
    By default the "l2tp bind" configuration option is used (if
    defined).

  * mode (optional): tunnel operating mode: lac (default) or lns.

Example with the telnet interface:
  accel-ppp# l2tp create tunnel peer-addr 192.0.2.1 host-addr 192.0.2.2

The above command tells accel-ppp to establish a new tunnel with the
peer at 192.0.2.1. The local address will be 192.0.2.2 and the tunnel
will operate as lac.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

When peer's port isn't known (i.e. right after a tunnel establishment
request has been sent), use the source port of the first peer's
response as the destination port of any future L2TP message sent over
that tunnel.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Send L2TP messages to the host set in the addr field of l2tp_packet_t,
instead of relying on the file descriptor's connection state. This
will allow the file descriptor to be disconnected (allowing it to
wait for a message from an arbitrary source port) while still being
able to retransmit previous L2TP messages.

This possibility is necessary for initiating tunnel establishment: the
initial SCCRQ is sent to the peer on port 1701, but the peer may reply
with an arbitrary source port. The socket thus needs to be disconnected
to be able to receive the peer's SCCRP. But in the mean time, the
initial SCCRQ may need to be retransmitted (if no answer is received
from the peer after a given amount of time). Hence the need for sending
L2TP messages over unconnected sockets.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Rename field lns_addr, as it identifies the host address, whether it be
a LAC or a LNS.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Rename field lac_addr, as it identifies the peer address, whether it be
a LAC or a LNS.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define the lns_mode flag for tunnels and sessions to keep track
of their operating state. A session's mode is inherited from its
parent tunnel.
The session's mode is used to set the PPPOL2TP_SO_LNSMODE socket
option to its PPP socket.
For tunnels, the mode is used to define how new sessions may be
created:
  -In LNS mode, new sessions may be created by accepting incomming
   calls (ICRQ) or by placing outgoing calls (OCRQ).
  -In LAC mode, tunnels will create sessions by accepting outgoing
   calls or by placing incomming calls.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Define STATE_WAIT_SCCRP which will be required for creating new tunnels
on behalf of the host. This state will be entered right after sending
an SCCRQ message.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Change the meaning of the Nr field in struct l2tp_conn_t: instead of
setting it to the last received message sequence, set it with the
value of the next expected message sequence number (i.e. one above
the previous value). This simplifies processing and avoids the
l2tp_send() function to increment the L2TP packet Nr field (it's now
directly set to the correct value).
Having Nr correctly set before calling l2tp_send() is necessary for
implementing tunnel establishment requests (SCCRQ messages) since the
Nr field of this message must be 0.

This patch also replaces the formula used to check if a message Ns is
lower than a tunnel Nr.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

When allocating tunnels, set the lns_addr field of tunnels using
getsockname() instead of using the "host" parameter. This will allow
the caller to pass an unspecified port in "host" (for binding to
any source port) and to set the lns_addr field with the address really
bound to.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>

Remove the "serv" parameter from l2tp_tunnel_alloc() prototype.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>