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Diffstat (limited to 'Documentation/filesystems/afs.txt')
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diff --git a/Documentation/filesystems/afs.txt b/Documentation/filesystems/afs.txt new file mode 100644 index 000000000000..2f4237dfb8c7 --- /dev/null +++ b/Documentation/filesystems/afs.txt @@ -0,0 +1,155 @@ + kAFS: AFS FILESYSTEM + ==================== + +ABOUT +===== + +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: + + (*) Write support. + (*) Communications security. + (*) Local caching. + (*) pioctl() system call. + (*) Automatic mounting of embedded mountpoints. + + +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 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. + +Once the module has been loaded, more modules can be added by the following +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. + +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 + + 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). + +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 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: + + (*) They cannot be listed. Running a program like "ls" on them will incur an + EREMOTE error (Object is remote). + + (*) Other objects can't be looked up inside of them. This also incurs an + EREMOTE error. + + (*) 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. + + (*) They can be mounted on (which symbolic links can't). + + +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 directory per cell that contains files that list volume location + servers, volumes, and active servers known within that cell. + + +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. + +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 18.7.14.88:128.2.191.224 >/proc/fs/afs/cells + +No other cell database operations are available at this time. + + +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 -S /tmp/rxrpc.o +insmod -S /tmp/kafs.o rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91 + +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 +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/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 rxrpc |