PLUMBER(4) PLUMBER(4) NAME plumber - file system for interprocess messaging SYNOPSIS plumber [ -p plumbing ] [ -s srvname ] 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, srvname, for mounting elsewhere. By default, its name is a dot-separated concatenation of the program's name and a process id. A different one can be specified via the -s option. 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 PLUMBER(4) PLUMBER(4) 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 messages that involve files in newly mounted services.