[AFS]: Update the AFS fs documentation.
Update the AFS fs documentation. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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David Howells
David S. Miller
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0795e7c031
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@ -1,31 +1,82 @@
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====================
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kAFS: AFS FILESYSTEM
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====================
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ABOUT
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Contents:
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- Overview.
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- Usage.
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- Mountpoints.
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- Proc filesystem.
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- The cell database.
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- Security.
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- Examples.
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========
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OVERVIEW
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========
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This filesystem provides a fairly simple secure AFS filesystem driver. It is
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under development and does not yet provide the full feature set. The features
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it does support include:
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(*) Security (currently only AFS kaserver and KerberosIV tickets).
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(*) File reading.
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(*) Automounting.
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It does not yet support the following AFS features:
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(*) Write support.
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(*) Local caching.
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(*) pioctl() system call.
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===========
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COMPILATION
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===========
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The filesystem should be enabled by turning on the kernel configuration
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options:
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CONFIG_AF_RXRPC - The RxRPC protocol transport
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CONFIG_RXKAD - The RxRPC Kerberos security handler
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CONFIG_AFS - The AFS filesystem
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Additionally, the following can be turned on to aid debugging:
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CONFIG_AF_RXRPC_DEBUG - Permit AF_RXRPC debugging to be enabled
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CONFIG_AFS_DEBUG - Permit AFS debugging to be enabled
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They permit the debugging messages to be turned on dynamically by manipulating
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the masks in the following files:
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/sys/module/af_rxrpc/parameters/debug
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/sys/module/afs/parameters/debug
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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 af_rxrpc.o
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insmod rxkad.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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The first module is the AF_RXRPC network protocol driver. This provides the
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RxRPC remote operation protocol and may also be accessed from userspace. See:
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Documentation/networking/rxrpc.txt
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The second module is the kerberos RxRPC security driver, and the third module
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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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@ -33,7 +84,7 @@ 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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volume location servers within that cell, with the latter separated by colons.
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Filesystems can be mounted anywhere by commands similar to the following:
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@ -42,11 +93,6 @@ Filesystems can be mounted anywhere by commands similar to the following:
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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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@ -60,55 +106,66 @@ 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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===========
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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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AFS has a concept of mountpoints. In AFS terms, these are specially formatted
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symbolic links (of the same form as the "device name" passed to mount). kAFS
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presents these to the user as directories that have a follow-link capability
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(ie: symbolic link semantics). If anyone attempts to access them, they will
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automatically cause the target volume to be mounted (if possible) on that site.
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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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Automatically mounted filesystems will be automatically unmounted approximately
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twenty minutes after they were last used. Alternatively they can be unmounted
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directly with the umount() system call.
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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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Manually unmounting an AFS volume will cause any idle submounts upon it to be
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culled first. If all are culled, then the requested volume will also be
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unmounted, otherwise error EBUSY will be returned.
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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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This can be used by the administrator to attempt to unmount the whole AFS tree
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mounted on /afs in one go by doing:
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(*) They can be mounted on (which symbolic links can't).
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umount /afs
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===============
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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 "cells" file that lists cells currently known to the afs module and
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their usage counts:
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[root@andromeda ~]# cat /proc/fs/afs/cells
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USE NAME
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3 cambridge.redhat.com
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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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[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/servers
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USE ADDR STATE
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4 172.16.18.91 0
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[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/vlservers
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ADDRESS
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172.16.18.91
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[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/volumes
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USE STT VLID[0] VLID[1] VLID[2] NAME
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1 Val 20000000 20000001 20000002 root.afs
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=================
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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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The filesystem maintains an internal database of all the cells it knows and the
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IP addresses of the volume location servers for those cells. The cell to which
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the system belongs is added to the database when insmod is performed by the
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"rootcell=" argument or, if compiled in, using a "kafs.rootcell=" argument on
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the kernel command line.
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Further cells can be added by commands similar to the following:
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@ -118,20 +175,65 @@ Further cells can be added by commands similar to the following:
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No other cell database operations are available at this time.
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========
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SECURITY
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========
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Secure operations are initiated by acquiring a key using the klog program. A
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very primitive klog program is available at:
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http://people.redhat.com/~dhowells/rxrpc/klog.c
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This should be compiled by:
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make klog LDLIBS="-lcrypto -lcrypt -lkrb4 -lkeyutils"
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And then run as:
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./klog
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Assuming it's successful, this adds a key of type RxRPC, named for the service
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and cell, eg: "afs@<cellname>". This can be viewed with the keyctl program or
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by cat'ing /proc/keys:
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[root@andromeda ~]# keyctl show
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Session Keyring
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-3 --alswrv 0 0 keyring: _ses.3268
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2 --alswrv 0 0 \_ keyring: _uid.0
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111416553 --als--v 0 0 \_ rxrpc: afs@CAMBRIDGE.REDHAT.COM
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Currently the username, realm, password and proposed ticket lifetime are
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compiled in to the program.
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It is not required to acquire a key before using AFS facilities, but if one is
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not acquired then all operations will be governed by the anonymous user parts
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of the ACLs.
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If a key is acquired, then all AFS operations, including mounts and automounts,
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made by a possessor of that key will be secured with that key.
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If a file is opened with a particular key and then the file descriptor is
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passed to a process that doesn't have that key (perhaps over an AF_UNIX
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socket), then the operations on the file will be made with key that was used to
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open the file.
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========
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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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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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insmod /tmp/rxrpc.o
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insmod /tmp/rxkad.o
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insmod /tmp/kafs.o rootcell=cambridge.redhat.com: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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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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@ -141,15 +243,7 @@ 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 rxkad
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rmmod rxrpc
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