connld.9

7号信令功能代码,为开源代码

.\"
.\" Copyright (C) 2000  John A. Boyd Jr.  protologos, LLC
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.\" Library General Public License for more details.
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.TH CONNLD 9 "24 Apr 2000" "LiS 2.9" "Linux STREAMS"
.SH NAME
.B connld
\- 
.B STREAMS
module supporting the generation of unique new
.BR STREAMS "\-based"
.I pipes
from an existing pipe end.
.SH DESCRIPTION
The
.B connld
module provides a means to generate multiple unique
.BR STREAMS "\-based"
.I pipes
from a single existing
.I pipe
end.
.sb
.B connld
may only be
.I pushed
(via the
.B "STREAMS I_PUSH"
.IR ioctl )
onto a
.BR STREAMS "\-based"
.IR pipe .
When first
.IR pushed ,
.B connld
does nothing; on each subsequent
.BR open "(2), "
.B connld
will generate a unique
.BR STREAMS "\-based"
.IR pipe .
One end of each new pipe replaces the original pipe end from the
perspective of the
.B open
call.
The other end of each new pipe is sent, effectively as if by
the
.B I_SENDFD
.IR ioctl ,
to the other end of the original pipe, ostensibly to be received
by a subsequent
.B I_RECVFD
.I ioctl
operation.
.SH "APPLICATION USAGE"
The intent of
.B connld
is to provide a means to generate unique pipes which separately
and independently connect client processes to a server process.
The point of access for such clients is expected to be a path
name known to all such clients and to which a pipe end may be
connected (via
.BR fattach "(3)) "
by the server process.
The server establishes the original pipe, pushes
.B connld
onto the client end, and then listens via
.B I_RECVFD
for new connections on the server end.
A client wishing to connect to the server will
.BR open "(2) "
the path name representing the client end, and can determine via
.BR isastream "(3) "
whether or not the server process is active and attached.  If 
it is, the
.BR open "() "
call returns one end of a unique new pipe that thus connects
the client to the server.
.sp
Such a server is responsible both for accepting new connections
via
.B I_RECVFD
on the original pipe, and for communicating with clients so
connected via the received pipe ends.
It would also be reasonable for such a server process to invalidate
the point of access by calling
.BR fdetach "(3) "
before terminating.
.sp
It should be noted that the
.BR poll "(2) "
primitive may be used to indicate when an 
.B M_PASSFP
representing a newly passed file is available on the original server
pipe end.
This is reflected by the
.B POLLIN
status setting in the
.B events
and
.B revents
fields of a
.B pollfd
structure.
Moreover, any attempt to read an
.B M_PASSFP
message via the data-receiving primitives (i.e., 
.BR read "(2), " getmsg "(3), and " getpmsg "(3)) "
will fail with
.BR errno "(3) "
returning an
.B EBADMSG
indication without discarding the message.
.sp
Even so, it should be reasonable to expect only
.B M_PASSFP
messages will be received on the original server pipe end,
since it is not possible to carry on normal data traffic which
has
.B connld
on one end, since
.B connld
does not support such traffic.
.sp
The use of
.B connld
can be made entirely free-standing by attaching well-known paths to
.I both
ends of the original pipe.  The relevant capabilities are implemented
in LiS so that the original creator of the
.B pipe
can close both ends after attaching paths to them, and the
process of passing file descriptors can still be carried out via
new
.BR open "()'s "
as long as both ends remain attached.
.SH "SEE ALSO"
.BR fattach "(3), "
.BR fattach "(8), "
.BR fdetach "(3), "
.BR fifo "(4), "
.BR fifo "(9), "
.BR pipe "(3), "
.BR STREAMS "(4) "
.SH HISTORY
Unix System V Release 4 (SVR4)
.SH AUTHOR
John Boyd, protologos LLC.