PLUMBER(4) PLUMBER(4)
NAME
plumber - file system for interprocess messaging
SYNOPSIS
plumber [ -p plumbing ]
DESCRIPTION
The plumber is a user-level file server that receives, exam-
ines, rewrites, and dispatches plumb(6) messages between
programs. Its behavior is programmed by a plumbing file
(default /usr/$user/lib/plumbing) in the format of plumb(6).
Its services are mounted on the directory /mnt/plumb
(/mnt/term/mnt/plumb on the CPU server) and consist of two
pre-defined files, send and rules, and a set of output ports
for dispatching messages to applications. The service is
also published as a srv(4) file, named in $plumbsrv, for
mounting elsewhere.
Programs use write (see read(2)) to deliver messages to the
send file, and read(2) to receive them from the correspond-
ing port. For example, sam(1)'s plumb menu item or the B
command cause a message to be sent to /mnt/plumb/send; sam
in turn reads from, by convention, /mnt/plumb/edit to
receive messages about files to open.
A copy of each message is sent to each client that has the
corresponding port open. If none has it open, and the rule
has a plumb client or plumb start rule, that rule is
applied. A plumb client rule causes the specified command
to be run and the message to be held for delivery when the
port is opened. A plumb start rule runs the command but
discards the message. If neither start or client is speci-
fied and the port is not open, the message is discarded and
a write error is returned to the sender.
The set of output ports is determined dynamically by the
specification in the plumbing rules file: a port is created
for each unique destination of a plumb to rule.
The set of rules currently active may be examined by reading
the file /mnt/plumb/rules; appending to this file adds new
rules to the set, while creating it (opening it with OTRUNC)
clears the rule set. Thus the rule set may be edited dynam-
ically with a traditional text editor. However, ports are
never deleted dynamically; if a new set of rules does not
include a port that was defined in earlier rules, that port
will still exist (although no new messages will be delivered
there).
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PLUMBER(4) PLUMBER(4)
FILES
/usr/$user/lib/plumbing default rules file
/sys/lib/plumb directory to search for files in
include statements
/mnt/plumb mount point for plumber(4).
SOURCE
/sys/src/cmd/plumb
SEE ALSO
plumb(1), plumb(2), plumb(6)
BUGS
Plumber's file name space is fixed, so it is difficult to
plumb messages that involve files in newly mounted services.
Page 2 Plan 9 (printed 12/27/24)