This is a simple draft document of the MimeFS translator I am doing.

The idea is to warp a filesystem tree with a deforming mirror: most of
the files  are accessed normally (like  a mirrorfs or  a symlink would
do), but actions can be  associated with special files, for example to
run a tarfs translator for tar files.

There are several parts in the mimefs:

- Identifying files

This  could be  done using  something similar  to the  'file' command;
reusing file's magic list. I fear this would be too expensive (opening
and reading a bit  of each seen file can cost a  lot, and even more if
you stack a mimefs on top of a ftpfs or nfs).

For the  first version, I think  that a regexp match  on filenames (to
match  extensions,  like  .tar.gz)  would  be  enough,  and  far  less
time-consuming.

Full identification using magic should be avaiable at user option, and
users should be able to enable it  on some part of the FS tree but not
on some others.

- Main handling system

The core system  will proceed RPC (implement the  netfs callbacks) and
call the appropritate functions of the plugins.

Plugins will handle part of the  filesystem tree. The idea is to avoid
having to  run a separate translator  for every special  node (like an
arfs for every .deb file  in /var/cache/apt/archive). So, we'll try to
have plugins (.so)  which can be loaded into mimefs  to proceed with a
specific type of files.

For  the first  version,  plugins will  only  support dir_readdir  and
io_read, to allow  people to, for example, cd into a  png and then cat
"x", "y", "comment", "depth"; or  to run readonly tarfs translators on
the  data.tar.gz inside .deb.  Only nodes  with underlying  ports will
support  other  functions  (like  nodes  mirrored  from  the  original
filesystem or nodes for autostarted translators).

- Translator running

The last part  of the main handling system will  be to run translators
like  tarfs   to  handle  mime-types;  and  will   then  mirror  those
translators as usual.

Of  course, all  that should  be recursive  (a .png  inside  a .tar.gz
inside a .deb should be handled like a normal .png).

- Basic mirroring plugin

This   plugin   will   handle   the   mirroring   of   an   underlying
filesystem.  It'll  be use  both  for  the  basic filesystem  and  for
mirroring (and warping) the trees of runned translators (like tarfs).

- Configuration file parser, command line parser

- Caching features

To improve performances, mimefs will not perform queries on underlying
trees  for each dir_readdir  or file_name_lookup,  but will  cache the
requests in its  own tree; a mean to detect  change son the underlying
node and then to invalidate our cache will be needed (notify ?)

More details will come soon ;)