9P (protocol)

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9P (or the Plan 9 Filesystem Protocol or Styx) is a network protocol developed for the Plan 9 from Bell Labs distributed operating system as the means of connecting the components of a Plan 9 system. Files are key objects in Plan 9. They represent windows, network connections, processes, and almost anything else available in the operating system.

9P was revised for the 4th edition of Plan 9 under the name 9P2000 that contained various[which?] fundamental improvements. The latest version of the Inferno operating system also uses 9P2000. The Inferno file protocol was originally called Styx, but technically it has always been a variant of 9P.

A server implementation of 9P for Unix, called u9fs, is included in the Plan 9 distribution. A 9P OS X client kernel extension is provided by Mac9P.[1] A kernel client driver for Linux is part of the v9fs project. 9P and its derivatives have also found application in embedded environments, such as the Styx on a Brick project.[2]

Server applications[edit]

Many of Plan 9's applications take the form of 9P file servers. Examples include:

  • acme: a text editor/development environment
  • rio: the Plan 9 windowing system
  • plumber: interprocess communication
  • ftpfs: an FTP client which presents the files and directories on a remote FTP server in the local namespace
  • wikifs: a wiki editing tool which presents a remote wiki as files in the local namespace
  • webfs: a file server that retrieves data from URLs and presents the contents and details of responses as files in the local namespace

Implementation[edit]

9P sends the following messages between clients and servers.[3] These messages correspond to the entry points in the Plan 9 vfs layer that any 9P server must implement.

version
Negotiate protocol version[4]
error
Return an error[5]
flush
Abort a message[6]
auth, attach
Establish a connection[7]
walk
Descend a directory hierarchy[8]
create, open
Prepare a fid for I/O on an existing or new file[9]
read, write
Transfer data from and to a file[10]
clunk
Forget about a fid[11]
remove
Remove a file from a server[12]
stat, wstat
Inquire or change file attributes[13]

See also[edit]

References[edit]

External links[edit]