plumber – file system for interprocess messaging
is a user-level file server that receives, examines, rewrites, and dispatches
messages between programs.
Its behavior is programmed by a
in the format of
Its services are mounted on the directory
on the CPU server) and consist of two
and a set of output
for dispatching messages to applications.
The service is also published as a
file, named in
for mounting elsewhere.
to deliver messages to the
to receive them from the corresponding port.
menu item or the
command cause a message to be sent to
in turn reads from, by convention,
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
rule, that rule is applied.
rule causes the specified command to be run
and the message to be held for delivery when the port is opened.
rule runs the command but discards the message.
is specified 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
The set of rules currently active may be examined by reading the file
appending to this file adds new rules to the set, while
creating it (opening it with
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).
default rules file
directory to search for files in
mount point for
file name space is fixed, so it is difficult to plumb
messages that involve files in newly mounted services.