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