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| -rw-r--r-- | 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 2f4237dfb8c7..12ad6c7f4e50 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 |