Known Solutions and Efforts (Linux)
1993 in the beginning there was ...
- it was discontinued in 1995.
1997 for kernel 2.0.x ...
- LOFS Linux Overlay Filesystem by (Benjamin C R LaHaise)?
- I'm unable to find the patches anywhere (lofs-2.0.30 ...)
1998 after some discussions on lkml ...
- OVLFS The Overlay Filesystem by (Arthur Naseef)?
- who seems to have disappeared in July 2001
- (there is one release at [ibiblio.org])
- The ovlfs-2.0 version is for linux-2.4 and was released in 2003 on [ovlfs.sf.net]
1999 as an academic work...
- wrapfs by ((Erez Zadok) (more info can be found on [his pages])
2001 as a part of the vserver project
- immutable linkage invert by Sam Vilain, not actually a new filesystem at all but simply seperation of the so-called immutable filesystem bit between immutability covering the inode, and immutability covering the directory entries, or linkage of the inode. Proved on ext2, ext3 and (briefly) reiserfs.
2001 a new effort and a new project ...
2002 as a part of the [UML] project
- the [Copy-On-Write layer] (COW) of the UML Block Driver (UBD) offers a useful approach, but appears to only be accessible to UML kernels and has not been generalised.
2002 an LD_PRELOAD module with unionfs like capabilities
2004 (March) as a thesis paper ...
- This filesystem is similar to the FreeBSD? union filesystem; the code is stable and already actively used in a telecommunications project within Siemens.
2004 (December) as a FUSE based fs
- [CopyFS] A copy-on-write, versionned filesystem
LUFS unionfs..
- [LUFS-based unionfs for Linux] Enhanced port from BSD: features as below, without restrictions on number of layers and mixed r/o and r/w permissions.
- [LUFS-based unionfs for Linux] A union file system allows the user to combine a read-only base directory and a writable overlay under a new read/write view. Initially, the view contains the files in the base. No changes are made as long as the contents of the view is accessed read-only. The overlay is updated as soon as the combined view is written. The idea comes from BSD's unionfs.
2004 [UnionFS] ... based on FiST?, working for 2.4 and 2.6 kernels
2004 TBVFS ... who knows?
Known Solutions and Efforts (OTHER)
- *BSD (4.4, BSDi, NetBSD?, FreeBSD?, OpenBSD?) have the "union" mount option. This is well documented. [mount_union(8)]
- Solaris has long had the "translucent" file system.
- The [vesta] source code management system has similar functionality. It works on linux and is currently maintained. It does not do exactly what you want, but you might be able to use their code. Currently their code exports an nfs filesystem (for portability) rather than a linux kernel filesystem, but I read a while back they were looking at making a kernel version.
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