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    Subject[PATCH 12/16] AFS: Update the AFS fs documentation [try #4]
    Date
    Update the AFS fs documentation.

    Signed-Off-By: David Howells <dhowells@redhat.com>
    ---

    Documentation/filesystems/afs.txt | 214 +++++++++++++++++++++++++++----------
    1 files changed, 154 insertions(+), 60 deletions(-)

    diff --git a/Documentation/filesystems/afs.txt b/Documentation/filesystems/afs.txt
    index 2f4237d..12ad6c7 100644
    --- a/Documentation/filesystems/afs.txt
    +++ b/Documentation/filesystems/afs.txt
    @@ -1,31 +1,82 @@
    + ====================
    kAFS: AFS FILESYSTEM
    ====================

    -ABOUT
    -=====
    +Contents:
    +
    + - Overview.
    + - Usage.
    + - Mountpoints.
    + - Proc filesystem.
    + - The cell database.
    + - Security.
    + - Examples.
    +
    +
    +========
    +OVERVIEW
    +========

    -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:
    +This filesystem provides a fairly simple secure AFS filesystem driver. It is
    +under development and does not yet provide the full feature set. The features
    +it does support include:

    - (*) Write support.
    - (*) Communications security.
    - (*) Local caching.
    - (*) pioctl() system call.
    - (*) Automatic mounting of embedded mountpoints.
    + (*) Security (currently only AFS kaserver and KerberosIV tickets).

    + (*) File reading.

    + (*) Automounting.
    +
    +It does not yet support the following AFS features:
    +
    + (*) Write support.
    +
    + (*) Local caching.
    +
    + (*) pioctl() system call.
    +
    +
    +===========
    +COMPILATION
    +===========
    +
    +The filesystem should be enabled by turning on the kernel configuration
    +options:
    +
    + CONFIG_AF_RXRPC - The RxRPC protocol transport
    + CONFIG_RXKAD - The RxRPC Kerberos security handler
    + CONFIG_AFS - The AFS filesystem
    +
    +Additionally, the following can be turned on to aid debugging:
    +
    + CONFIG_AF_RXRPC_DEBUG - Permit AF_RXRPC debugging to be enabled
    + CONFIG_AFS_DEBUG - Permit AFS debugging to be enabled
    +
    +They permit the debugging messages to be turned on dynamically by manipulating
    +the masks in the following files:
    +
    + /sys/module/af_rxrpc/parameters/debug
    + /sys/module/afs/parameters/debug
    +
    +
    +=====
    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 af_rxrpc.o
    + insmod rxkad.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.
    +The first module is the AF_RXRPC network protocol driver. This provides the
    +RxRPC remote operation protocol and may also be accessed from userspace. See:
    +
    + Documentation/networking/rxrpc.txt
    +
    +The second module is the kerberos RxRPC security driver, and the third module
    +is the actual filesystem driver for the AFS filesystem.

    Once the module has been loaded, more modules can be added by the following
    procedure:
    @@ -33,7 +84,7 @@ 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.
    +volume location servers within that cell, with the latter separated by colons.

    Filesystems can be mounted anywhere by commands similar to the following:

    @@ -42,11 +93,6 @@ Filesystems can be mounted anywhere by commands similar to the following:
    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).
    @@ -60,55 +106,66 @@ 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:
    +AFS has a concept of mountpoints. In AFS terms, 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 a follow-link capability
    +(ie: symbolic link semantics). If anyone attempts to access them, they will
    +automatically cause the target volume to be mounted (if possible) on that site.

    - (*) They cannot be listed. Running a program like "ls" on them will incur an
    - EREMOTE error (Object is remote).
    +Automatically mounted filesystems will be automatically unmounted approximately
    +twenty minutes after they were last used. Alternatively they can be unmounted
    +directly with the umount() system call.

    - (*) Other objects can't be looked up inside of them. This also incurs an
    - EREMOTE error.
    +Manually unmounting an AFS volume will cause any idle submounts upon it to be
    +culled first. If all are culled, then the requested volume will also be
    +unmounted, otherwise error EBUSY will be returned.

    - (*) 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.
    +This can be used by the administrator to attempt to unmount the whole AFS tree
    +mounted on /afs in one go by doing:

    - (*) They can be mounted on (which symbolic links can't).
    + umount /afs


    +===============
    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 "cells" file that lists cells currently known to the afs module and
    + their usage counts:
    +
    + [root@andromeda ~]# cat /proc/fs/afs/cells
    + USE NAME
    + 3 cambridge.redhat.com

    (*) A directory per cell that contains files that list volume location
    servers, volumes, and active servers known within that cell.

    + [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/servers
    + USE ADDR STATE
    + 4 172.16.18.91 0
    + [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/vlservers
    + ADDRESS
    + 172.16.18.91
    + [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/volumes
    + USE STT VLID[0] VLID[1] VLID[2] NAME
    + 1 Val 20000000 20000001 20000002 root.afs

    +
    +=================
    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.
    +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 system belongs is added to the database when insmod is performed by the
    +"rootcell=" argument or, if compiled in, using a "kafs.rootcell=" argument on
    +the kernel command line.

    Further cells can be added by commands similar to the following:

    @@ -118,20 +175,65 @@ Further cells can be added by commands similar to the following:
    No other cell database operations are available at this time.


    +========
    +SECURITY
    +========
    +
    +Secure operations are initiated by acquiring a key using the klog program. A
    +very primitive klog program is available at:
    +
    + http://people.redhat.com/~dhowells/rxrpc/klog.c
    +
    +This should be compiled by:
    +
    + make klog LDLIBS="-lcrypto -lcrypt -lkrb4 -lkeyutils"
    +
    +And then run as:
    +
    + ./klog
    +
    +Assuming it's successful, this adds a key of type RxRPC, named for the service
    +and cell, eg: "afs@<cellname>". This can be viewed with the keyctl program or
    +by cat'ing /proc/keys:
    +
    + [root@andromeda ~]# keyctl show
    + Session Keyring
    + -3 --alswrv 0 0 keyring: _ses.3268
    + 2 --alswrv 0 0 \_ keyring: _uid.0
    + 111416553 --als--v 0 0 \_ rxrpc: afs@CAMBRIDGE.REDHAT.COM
    +
    +Currently the username, realm, password and proposed ticket lifetime are
    +compiled in to the program.
    +
    +It is not required to acquire a key before using AFS facilities, but if one is
    +not acquired then all operations will be governed by the anonymous user parts
    +of the ACLs.
    +
    +If a key is acquired, then all AFS operations, including mounts and automounts,
    +made by a possessor of that key will be secured with that key.
    +
    +If a file is opened with a particular key and then the file descriptor is
    +passed to a process that doesn't have that key (perhaps over an AF_UNIX
    +socket), then the operations on the file will be made with key that was used to
    +open the file.
    +
    +
    +========
    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
    +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
    +insmod /tmp/rxrpc.o
    +insmod /tmp/rxkad.o
    +insmod /tmp/kafs.o rootcell=cambridge.redhat.com: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
    +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
    @@ -141,15 +243,7 @@ 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 rxkad
    rmmod rxrpc
    -
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