ref: 18169e03de5f44f1dd8fa1e355dd166cab983e50
dir: /sys/man/4/plumber/
.TH PLUMBER 4 .SH NAME plumber \- file system for interprocess messaging .SH SYNOPSIS .B plumber [ .B -p .I plumbing ] .SH DESCRIPTION The .I plumber is a user-level file server that receives, examines, rewrites, and dispatches .IR plumb (6) messages between programs. Its behavior is programmed by a .I plumbing file (default .BR /usr/$user/lib/plumbing ) in the format of .IR plumb (6). .PP Its services are mounted on the directory .B /mnt/plumb .RB ( /mnt/term/mnt/plumb on the CPU server) and consist of two pre-defined files, .B send and .BR rules , and a set of output .I ports for dispatching messages to applications. The service is also published as a .IR srv (4) file, named in .BR $plumbsrv , for mounting elsewhere. .PP Programs use .B write (see .IR read (2)) to deliver messages to the .B send file, and .IR read (2) to receive them from the corresponding port. For example, .IR sam (1)'s .B plumb menu item or the .B B command cause a message to be sent to .BR /mnt/plumb/send ; .B sam in turn reads from, by convention, .B /mnt/plumb/edit to receive messages about files to open. .PP A copy of each message is sent to each client that has the corresponding port open. If none has it open, and the rule has a .B plumb .B client or .B plumb .B start rule, that rule is applied. A .B plumb .B client rule causes the specified command to be run and the message to be held for delivery when the port is opened. A .B plumb .B start rule runs the command but discards the message. If neither .B start or .B client is specified and the port is not open, the message is discarded and a write error is returned to the sender. .PP The set of output ports is determined dynamically by the specification in the plumbing rules file: a port is created for each unique destination of a .B plumb .B to rule. .PP The set of rules currently active may be examined by reading the file .BR /mnt/plumb/rules ; appending to this file adds new rules to the set, while creating it (opening it with .BR OTRUNC ) clears the rule set. Thus the rule set may be edited dynamically with a traditional text editor. However, ports are never deleted dynamically; if a new set of rules does not include a port that was defined in earlier rules, that port will still exist (although no new messages will be delivered there). .SH FILES .TF /usr/$user/lib/plumbing .TP .B /usr/$user/lib/plumbing default rules file .TP .B /sys/lib/plumb directory to search for files in .B include statements .TP .B /mnt/plumb mount point for .IR plumber (4). .SH SOURCE .B /sys/src/cmd/plumb .SH "SEE ALSO" .IR plumb (1), .IR plumb (2), .IR plumb (6) .SH BUGS .IR Plumber 's file name space is fixed, so it is difficult to plumb messages that involve files in newly mounted services.