sunos TFS.4s
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NAME
tfs, TFS - translucent file service
CONFIG
optionsTFS
SYNOPSIS
#include <sys/mount.h>
mount("tfs", dir, M NEWTYPE|flags, nfsargs);
DESCRIPTION
The translucent file service (TFS) supplies a copy-on-write
filesystem allowing users to share file hierarchies while
providing each user with a private hierarchy into which
files are copied as they are modified. Consequently, users
are isolated from each other's changes.
nfsargs specifies NFS style mount(2V) arguments, including
the address of the file server (the tfsd(8)) and the file
handle to be mounted. dir is the directory on which the TFS
filesystem is to be mounted.
TFS allows a user to mount a private, writable filesystem in
front of any number of public, read-only filesystems in such
a way that the contents of the public filesystems remain
visible behind the contents of the private filesystem. Any
change made to a file that is being shared from a public
filesystem will cause that file to be copied into the
private filesystem, where the modification will be per-
formed.
A directory in a TFS filesystem consists of a number of
stacked directories. The searchpath TFS uses to look up a
file in a directory corresponds to the stacking order: the
TFS will search the "frontmost" directory first, then the
directory behind it, and so on until the first occurrence of
the file is found. Modifications to a file can be made only
in the frontmost directory. TFS copies a file to the
frontmost directory when the file is opened for writing with
open(2V) or when its stat(2V) attributes are changed.
If a user removes a file which is not in the frontmost
directory, TFS creates a whiteout entry in the frontmost
directory and leaves the file intact in the back directory.
This whiteout entry makes it appear that the file no longer
exists, although the file can be reinstated in the directory
by using the unwhiteout(1) command to remove the whiteout
entry. The lsw(1) command lists whiteout entries.
TFS filesystems are served by the tfsd(8). A TFS filesystem
is mounted on a directory by making a TFS MOUNT protocol
request of the tfsd, specifying the directories that are to
be stacked. The tfsd responds with a file handle, which the
client then supplies to the mount(2V) system call, along
with the address of the tfsd.
SEE ALSO
lsw(1), unwhiteout(1),