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Diffstat (limited to 'kernel/Documentation/filesystems/afs.txt')
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diff --git a/kernel/Documentation/filesystems/afs.txt b/kernel/Documentation/filesystems/afs.txt new file mode 100644 index 000000000..ffef91c4e --- /dev/null +++ b/kernel/Documentation/filesystems/afs.txt @@ -0,0 +1,247 @@ + ==================== + kAFS: AFS FILESYSTEM + ==================== + +Contents: + + - Overview. + - Usage. + - Mountpoints. + - Proc filesystem. + - The cell database. + - Security. + - Examples. + + +======== +OVERVIEW +======== + +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: + + (*) Security (currently only AFS kaserver and KerberosIV tickets). + + (*) File reading and writing. + + (*) Automounting. + + (*) Local caching (via fscache). + +It does not yet support the following AFS features: + + (*) 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/kafs/parameters/debug + + +===== +USAGE +===== + +When inserting the driver modules the root cell must be specified along with a +list of volume location server IP addresses: + + modprobe af_rxrpc + modprobe rxkad + modprobe kafs rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91 + +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: + + echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/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, with the latter separated by colons. + +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 + +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 modprobe. + +Additional cells can be added through /proc (see later section). + + +=========== +MOUNTPOINTS +=========== + +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. + +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. + +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. + +This can be used by the administrator to attempt to unmount the whole AFS tree +mounted on /afs in one go by doing: + + umount /afs + + +=============== +PROC FILESYSTEM +=============== + +The AFS modules creates a "/proc/fs/afs/" directory and populates it: + + (*) 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 system belongs is added to the database when modprobe 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: + + echo add CELLNAME VLADDR[:VLADDR][:VLADDR]... >/proc/fs/afs/cells + echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells + +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 +some public volumes volumes. + +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 18.9.48.14:128.2.203.61:130.237.48.87 > /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 +rmmod kafs +rmmod rxkad +rmmod rxrpc |