Using plumbing
D1361603512
Amycroftiv
#Plumbing is a mechanism for passing messages between applications.
#It has a customizable set of rules (see [plumb(6) |
#http://plan9.bell-labs.com/magic/man2html/6/plumb]) to process
#incoming messages and dispatch them to target applications.
#
#The [plumber(4) |
#http://plan9.bell-labs.com/magic/man2html/4/plumber] is the file
#server that performs the message processing and dispatch.
#
#It is up to each application how it wishes to use this mechanism,
#but in the user-interface domain, the mechanism often allows the
#user to point to a file-name or URL and have the associated resource
#processed by an appropriate application.
#
#EXAMPLES
#
#In the rc shell window you can select or position the text cursor
#inside a piece of text and press button 2 and select "plumb" from
#the pop-up menu. Depending on what the text is, the plumber will
#perform different actions. For example:
#
# *	a .ps, .pdf, or .dvi file name invokes the [page(1) |
#	http://plan9.bell-labs.com/magic/man2html/1/page] display program
# *	a .gif, .jpg, .png, .ppm file name also invokes page(1) to
#	display them
# *	a compiler error message indicating a file and line number will
#	invoke the default text editor to open the file at the given line
#	number
# *	a .h file name will search /sys/include for the given header and
#	opens it in the default text editor
# *	a man(1) page reference invokes man(1) for the appropriate page
# *	a URL opens the default browser for that page
#
#The plumber can provide easy shortcuts for common functions. For
#example, given a script 'web' which takes an argument of a URL to
#open in a web browser, the plumbing rule:
#! 	# RFC's from one of the nicer-looking repositories.
#! 	type is text
#! 	data matches 'RFC:([0-9]+)'
#! 	plumb to web
#! 	plumb start web http://rfc.sunsite.dk/rfc/rfc$1.html
#will make RFC:2325 a link to some of the IETF's better work. A
#number of other potentially useful [plumbing examples] have been
#collected.
#
#A NICE TRICK
#
#Namespaces in Plan 9 are local. That is, if you're inside an
#application that has forked the namespace, you can't change the
#namespace visible to other applications. In particular, you can't
#mount a remote file server and then plumb it to another running
#application. Here's a neat trick that lets you do that.
#
#! 	srvfs plumbspace /n
#! 	plumber
#! 	rfork n
#! 	mount -b /srv/plumbspace /n
#
#Put this in your /lib/profile (before rio is started) and /n is now
#an indirect part of the namespace that can be changed in all
#applications by the plumber. An extra rule in the plumber is all
#that's needed to make use of it:
#
#! type is text
#! data matches 'Local (.*)'
#! plumb to none
#! plumb start rc -c $1
#
#For example, say I wished to mount a local kfs disk and edit a file
#in it. I can open a new shell window, type:
#
#! disk/kfs
#! plumb 'Local mount /srv/kfs /n/kfs'
#
#and the files on the new disk will be visible to all applications on
#the machine, including, for example, an existing incarnation of Acme.
#
#PLUMBING BETWEEN MACHINES ON A GRID
#
#The plumber is a good example of the power of network transparency
#in Plan 9. On a well-connected grid, the plumber will naturally act
#to dispatch messages to applications running on the correct machine.
#Consider a small grid of 3 machines: terminal, file/cpu/auth, and
#tcp boot cpu. The user's primary work environment is via cpu(1) to
#the file/cpu/auth server. A web browser runs on the terminal, and an
#acme(1) editing and compiling environment runs in a separate cpu(1)
#session to the tcp boot cpu server.
#
#As the user works within the primary cpu workspace, plumbed messages
#will find the correct destination automatically. Messages of url
#form will be received by the browser running on the local terminal
#and links will open there, messages referencing source code files
#will be received by the editor and appear for editing and
#compilation on the tcp boot cpu, and messages for applications
#running on the main cpu will be processed there.
#
#The necessary condition for this correct message dispatch between
#nodes is simply that all applications running on the grid have a
#connection to the plumber within their namespace, and have a view of
#file namespace which allows them to access any necessary resources.
#Programs which the user is interacting with directly should
#automatically have the plumber available at /mnt/plumb or
#/mnt/term/mnt/plumb; other programs will need to mount the user's
#plumber from /srv, possibly after an import(4) of the /srv of the
#machine hosting the plumber.
#
#ADDITIONAL REFERENCES
#
#[Plumbing and Other Utilities |
#http://plan9.bell-labs.com/sys/doc/plumb.html] - A paper on the
#design and implementation of the plumbing system.
#