lib/libnetgraph/netgraph.3

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.\" Author: Archie Cobbs <archie@whistle.com>
.\"
.\" $FreeBSD: src/lib/libnetgraph/netgraph.3,v 1.4.2.10 2002/12/29 16:35:36 schweikh Exp $
.\" $DragonFly: src/lib/libnetgraph/netgraph.3,v 1.2 2003/06/17 04:26:50 dillon Exp $
.\" $Whistle: netgraph.3,v 1.7 1999/01/25 07:14:06 archie Exp $
.\"
.Dd January 19, 1999
.Dt NETGRAPH 3
.Os
.Sh NAME
.Nm NgMkSockNode ,
.Nm NgNameNode ,
.Nm NgSendMsg ,
.Nm NgRecvMsg ,
.Nm NgSendData ,
.Nm NgRecvData ,
.Nm NgSetDebug ,
.Nm NgSetErrLog
.Nd netgraph user library
.Sh LIBRARY
.Lb libnetgraph
.Sh SYNOPSIS
.In netgraph.h
.Ft int
.Fn NgMkSockNode "const char *name" "int *csp" "int *dsp"
.Ft int
.Fn NgNameNode "int cs" "const char *path" "const char *fmt" "..."
.Ft int
.Fn NgSendMsg "int cs" "const char *path" "int cookie" "int cmd" "const void *arg" "size_t arglen"
.Ft int
.Fn NgSendAsciiMsg "int cs" "const char *path" "const char *fmt" "..."
.Ft int
.Fn NgSendMsgReply "int cs" "const char *path" "struct ng_mesg *msg" "const void *arg" "size_t arglen"
.Ft int
.Fn NgRecvMsg "int cs" "struct ng_mesg *rep" "size_t replen" "char *path"
.Ft int
.Fn NgRecvAsciiMsg "int cs" "struct ng_mesg *rep" "size_t replen" "char *path"
.Ft int
.Fn NgSendData "int ds" "const char *hook" "const u_char *buf" "size_t len"
.Ft int
.Fn NgRecvData "int ds" "u_char *buf" "size_t len" "char *hook"
.Ft int
.Fn NgSetDebug "int level"
.Ft void
.Fn NgSetErrLog "void (*log)(const char *fmt, ...)" "void (*logx)(const char *fmt, ...)"
.Sh DESCRIPTION
These functions facilitate user-mode program participation in the kernel
.Xr netgraph 4
graph-based networking system, by utilizing the netgraph
.Em socket
node type (see
.Xr ng_socket 4 ) .
.Pp
.Fn NgMkSockNode
should be called first, to create a new
.Em socket
type netgraph node with associated control and data sockets.  If
.Fa name
is non-NULL, the node will have that global name assigned to it.
.Fa "*csp"
and
.Fa "*dsp"
will be set to the newly opened control and data sockets
associated with the node; either
.Fa "csp"
or
.Fa "dsp"
may be NULL if only one socket is desired.
.Fn NgMkSockNode
loads the socket node type KLD if it's not already loaded.
.Pp
.Fn NgNameNode
assigns a global name to the node addressed by
.Fa path .
.Pp
.Fn NgSendMsg
sends a binary control message from the socket node associated
with control socket
.Fa cs
to the node addressed by
.Fa path .
The
.Fa cookie
indicates how to interpret
.Fa cmd ,
which indicates a specific command.
Extra argument data (if any) is specified by
.Fa arg
and
.Fa arglen .
The
.Fa cookie ,
.Fa cmd ,
and argument data are defined by the header file corresponding
to the type of the node being addressed.
The unique, non-negative token value chosen for use in the message
header is returned.  This value is typically used to associate replies.
.Pp
Use
.Fn NgSendMsgReply
to send reply to a previously received control message.
The original message header should be pointed to by
.Fa msg .
.Pp
.Fn NgSendAsciiMsg
performs the same function as
.Fn NgSendMsg ,
but adds support for
.Tn ASCII
encoding of control messages.
.Fn NgSendAsciiMsg
formats its input a la
.Xr printf 3
and then sends the resulting
.Tn ASCII
string to the node in a
.Dv NGM_ASCII2BINARY
control message.  The node returns a binary version of the
message, which is then sent back to the node just as with
.Fn NgSendMsg .
As with
.Fn NgSendMsg ,
the message token value is returned.
Note that
.Tn ASCII
conversion may not be supported by all node types.
.Pp
.Fn NgRecvMsg
reads the next control message received by the node associated with
control socket
.Fa cs .
The message and any extra argument data must fit in
.Fa replen
bytes.
If
.Fa "path"
is non-NULL, it must point to a buffer of at least
.Dv "NG_PATHLEN + 1"
bytes, which will be filled in (and NUL terminated) with the path to
the node from which the message was received.
.Pp
The length of the control message is returned.
A return value of zero indicates that the socket was closed.
.Pp
.Fn NgRecvAsciiMsg
works exactly like
.Fn NgRecvMsg ,
except that after the message is received, any binary arguments
are converted to
.Tn ASCII
by sending a
.Dv NGM_BINARY2ASCII
request back to the originating node.  The result is the same as
.Fn NgRecvAsciiMsg ,
with the exception that the reply arguments field will contain
a NUL-terminated
.Tn ASCII
version of the arguments (and the reply
header argument length field will be adjusted).
.Pp
.Fn NgSendData
writes a data packet out on the specified hook of the node corresponding
to data socket
.Fa ds .
The node must already be connected to some other node via that hook.
.Pp
.Fn NgRecvData
reads the next data packet (of up to
.Fa len
bytes) received by the node corresponding to data socket
.Fa ds
and stores it in
.Fa buf ,
which must be large enough to hold the entire packet.  If
.Fa "hook"
is non-NULL, it must point to a buffer of at least
.Dv "NG_HOOKLEN + 1"
bytes, which will be filled in (and NUL terminated) with the name of
the hook on which the data was received.
.Pp
The length of the packet is returned.
A return value of zero indicates that the socket was closed.
.Pp
.Fn NgSetDebug
and
.Fn NgSetErrLog
are used for debugging.
.Fn NgSetDebug
sets the debug level (if non-negative), and returns the old setting.
Higher debug levels result in more verbosity.  The default is zero.
All debug and error messages are logged via the functions
specified in the most recent call to
.Fn NgSetErrLog .
The default logging functions are
.Xr vwarn 3
and
.Xr vwarnx 3 .
.Pp
At debug level 3, the library attempts to display control message arguments
in
.Tn ASCII
format; however, this results in additional messages being
sent which may interfere with debugging.  At even higher levels,
even these additional messages will be displayed, etc.
.Pp
Note that
.Xr select 2
can be used on the data and the control sockets to detect the presence of
incoming data and control messages, respectively.
Data and control packets are always written and read atomically, i.e.,
in one whole piece.
.Pp
User mode programs must be linked with the
.Dv -lnetgraph
flag to link in this library.
.Sh INITIALIZATION
To enable Netgraph in your kernel, either your kernel must be
compiled with
.Dq options NETGRAPH
in the kernel configuration
file, or else the
.Xr netgraph 4
and
.Xr ng_socket 4
KLD modules must have been loaded via
.Xr kldload 8 .
.Sh RETURN VALUES
.Fn NgSetDebug
returns the previous debug setting.
.Fn NgSetErrLog
has no return value.
All other functions return \-1 if there was an error and set
.Va errno
accordingly.
A return value of zero from
.Fn NgRecvMsg
or
.Fn NgRecvData
indicates that the netgraph socket has been closed.
.Pp
For
.Fn NgSendAsciiMsg
and
.Fn NgRecvAsciiMsg ,
the following additional errors are possible:
.Bl -tag -width Er
.It Bq Er ENOSYS
The node type does not know how to encode or decode the control message.
.It Bq Er ERANGE
The encoded or decoded arguments were too long for the supplied buffer.
.It Bq Er ENOENT
An unknown structure field was seen in an
.Tn ASCII
control message.
.It Bq Er EALREADY
The same structure field was specified twice in an
.Tn ASCII
control message.
.It Bq Er EINVAL
.Tn ASCII
control message parse error or illegal value.
.It Bq Er E2BIG
ASCII control message array or fixed width string buffer overflow.
.El
.Sh SEE ALSO
.Xr select 2 ,
.Xr socket 2 ,
.Xr warnx 3 ,
.Xr kld 4 ,
.Xr netgraph 4 ,
.Xr ng_socket 4
.Sh HISTORY
The
.Nm netgraph
system was designed and first implemented at Whistle Communications, Inc. in
a version of
.Fx 2.2
customized for the Whistle InterJet.
.Sh AUTHORS
.An Archie Cobbs Aq archie@whistle.com