term% cat index.txt PLUMBER(4) Kernel Interfaces Manual PLUMBER(4)
NAME
plumber - file system for interprocess messaging
SYNOPSIS
plumber [ -p plumbing ]
DESCRIPTION
The plumber is a user-level file server that receives, examines,
rewrites, and dispatches plumb(6) messages between programs. Its be‐
havior is programmed by a plumbing file (default /usr/$user/lib/plumb‐
ing) 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 mes‐
sages to applications. The service is also published as a srv(4) file,
named in $plumbsrv, for mounting elsewhere.
Programs use write (see read(2)) to deliver messages to the send file,
and read(2) to receive them from the corresponding port. For example,
sam(1)'s plumb menu item or the B command cause a message to be sent to
/mnt/plumb/send; sam in turn reads from, by convention, /mnt/plumb/edit
to receive messages about files to open.
A copy of each message is sent to each client that has the correspond‐
ing port open. If none has it open, and the rule has a plumb client or
plumb start rule, that rule is applied. A plumb client rule causes the
specified command to be run and the message to be held for delivery
when the port is opened. A plumb start rule runs the command but dis‐
cards the message. If neither start or client is specified and the
port is not open, the message is discarded and a write error is re‐
turned to the sender.
The set of output ports is determined dynamically by the specification
in the plumbing rules file: a port is created for each unique destina‐
tion of a plumb to rule.
The set of rules currently active may be examined by reading the file
/mnt/plumb/rules; appending to this file adds new rules to the set,
while creating it (opening it with OTRUNC) clears the rule set. Thus
the rule set may be edited dynamically with a traditional text editor.
However, ports are never deleted dynamically; if a new set of rules
does not include a port that was defined in earlier rules, that port
will still exist (although no new messages will be delivered there).
FILES
/usr/$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 mes‐
sages that involve files in newly mounted services.
PLUMBER(4)