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afs.txt
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kAFS: AFS FILESYSTEM
====================
ABOUT
=====
This filesystem provides a fairly simple AFS filesystem driver. It is under
development and only provides very basic facilities. It does not yet support
the following AFS features:
(*) Write support.
(*) Communications security.
(*) Local caching.
(*) pioctl() system call.
(*) Automatic mounting of embedded mountpoints.
USAGE
=====
When inserting the driver modules the root cell must be specified along with a
list of volume location server IP addresses:
insmod rxrpc.o
insmod kafs.o rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91
The first module is a driver for the RxRPC remote operation protocol, and the
second is the actual filesystem driver for the AFS filesystem.
Once the module has been loaded, more modules can be added by the following
procedure:
echo add grand.central.org 18.7.14.88:128.2.191.224 >/proc/fs/afs/cells
Where the parameters to the "add" command are the name of a cell and a list of
volume location servers within that cell.
Filesystems can be mounted anywhere by commands similar to the following:
mount -t afs "%cambridge.redhat.com:root.afs." /afs
mount -t afs "#cambridge.redhat.com:root.cell." /afs/cambridge
mount -t afs "#root.afs." /afs
mount -t afs "#root.cell." /afs/cambridge
NB: When using this on Linux 2.4, the mount command has to be different,
since the filesystem doesn't have access to the device name argument:
mount -t afs none /afs -ovol="#root.afs."
Where the initial character is either a hash or a percent symbol depending on
whether you definitely want a R/W volume (hash) or whether you'd prefer a R/O
volume, but are willing to use a R/W volume instead (percent).
The name of the volume can be suffixes with ".backup" or ".readonly" to
specify connection to only volumes of those types.
The name of the cell is optional, and if not given during a mount, then the
named volume will be looked up in the cell specified during insmod.
Additional cells can be added through /proc (see later section).
MOUNTPOINTS
===========
AFS has a concept of mountpoints. These are specially formatted symbolic links
(of the same form as the "device name" passed to mount). kAFS presents these
to the user as directories that have special properties:
(*) They cannot be listed. Running a program like "ls" on them will incur an
EREMOTE error (Object is remote).
(*) Other objects can't be looked up inside of them. This also incurs an
EREMOTE error.
(*) They can be queried with the readlink() system call, which will return
the name of the mountpoint to which they point. The "readlink" program
will also work.
(*) They can be mounted on (which symbolic links can't).
PROC FILESYSTEM
===============
The rxrpc module creates a number of files in various places in the /proc
filesystem:
(*) Firstly, some information files are made available in a directory called
"/proc/net/rxrpc/". These list the extant transport endpoint, peer,
connection and call records.
(*) Secondly, some control files are made available in a directory called
"/proc/sys/rxrpc/". Currently, all these files can be used for is to
turn on various levels of tracing.
The AFS modules creates a "/proc/fs/afs/" directory and populates it:
(*) A "cells" file that lists cells currently known to the afs module.
(*) A directory per cell that contains files that list volume location
servers, volumes, and active servers known within that cell.
THE CELL DATABASE
=================
The filesystem maintains an internal database of all the cells it knows and
the IP addresses of the volume location servers for those cells. The cell to
which the computer belongs is added to the database when insmod is performed
by the "rootcell=" argument.
Further cells can be added by commands similar to the following:
echo add CELLNAME VLADDR[:VLADDR][:VLADDR]... >/proc/fs/afs/cells
echo add grand.central.org 18.7.14.88:128.2.191.224 >/proc/fs/afs/cells
No other cell database operations are available at this time.
EXAMPLES
========
Here's what I use to test this. Some of the names and IP addresses are local
to my internal DNS. My "root.afs" partition has a mount point within it for
some public volumes volumes.
insmod -S /tmp/rxrpc.o
insmod -S /tmp/kafs.o rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91
mount -t afs \%root.afs. /afs
mount -t afs \%cambridge.redhat.com:root.cell. /afs/cambridge.redhat.com/
echo add grand.central.org 18.7.14.88:128.2.191.224 > /proc/fs/afs/cells
mount -t afs "#grand.central.org:root.cell." /afs/grand.central.org/
mount -t afs "#grand.central.org:root.archive." /afs/grand.central.org/archive
mount -t afs "#grand.central.org:root.contrib." /afs/grand.central.org/contrib
mount -t afs "#grand.central.org:root.doc." /afs/grand.central.org/doc
mount -t afs "#grand.central.org:root.project." /afs/grand.central.org/project
mount -t afs "#grand.central.org:root.service." /afs/grand.central.org/service
mount -t afs "#grand.central.org:root.software." /afs/grand.central.org/software
mount -t afs "#grand.central.org:root.user." /afs/grand.central.org/user
umount /afs/grand.central.org/user
umount /afs/grand.central.org/software
umount /afs/grand.central.org/service
umount /afs/grand.central.org/project
umount /afs/grand.central.org/doc
umount /afs/grand.central.org/contrib
umount /afs/grand.central.org/archive
umount /afs/grand.central.org
umount /afs/cambridge.redhat.com
umount /afs
rmmod kafs
rmmod rxrpc