[H-GEN] Podfuk

[Jason Henry Parker]

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All,

I found this little gem after adding network block device support to
my kernel[1].

The name comes from ``POrtable Dodgy Filesystems in Userland
(hacK!)'', which apparently means something like ``fiddle'' in Czech,
but I prefer the imagery invoked when you read it in English.  :)

As you might have guessed, podfuk provides user-space kernels, sort of
like mach or something, by pretending to be coda venus cache manager.
Why would you want to do this?  The author gives an example:

pavel at Elf:/$ cd "/tmp/unarj241a.tar.gz#utar/unarj241a"/
pavel at Elf:/tmp/unarj241a.tar.gz#utar/unarj241a$ ls
Makefile       os2unarj.mak   tccunarj.mak   unarj.doc
Makefile.orig  patch241a      technote.doc   unarj.exe
decode.c       qclunarj.mak   unarj.c        unarj.h
environ.c      readme.doc     unarj.def      unarj.h.orig
pavel at Elf:/tmp/unarj241a.tar.gz#utar/unarj241a$ cd /tmp
pavel at Elf:/tmp$ head mc.diff.gz#ugz
--- /dev/null   Sun Jun  2 15:30:20 1996
+++ mmc/vfs/shared.c    Mon Mar 30 23:41:55 1998
@@ -0,0 +1,267 @@

The examples I've seen seem to indicate that tar, gzip, arj, and ftp
filesystems are available.

That's pretty nifty, but not the end.  Not by a long shot.  There's a
kernel patch required, and at the top of podfuk.c, we see this:

    #if 0
    ifdef notdef
    *
    * POrtable Dodgy Filesystems in Userland (this used to be hacK!)
    *                alias podfuk (v2)
    ...
    * Notice this file is *evil*. It is both valid c source and working
    * Makefile. You might want to ln -s podfuk.c Makefile.
    ...
    endif
    ...(makefile stuff)...
    ifdef donotdefine
    #endif
    ...(C source file stuff)...
    
   /* Coda/Venus in a nutshell:
    * Coda is a filesystem, lives in the kernel
    * Venus is an app; podfuk is a replacement for venus
    * When a coda mount needs service, it sends a message
    *   up to podfuk through a pipe
    * Coda/Podfuk both open /dev/cfs0 and make ioctl calls
    * Message includes ViceFid (coda file/dir handle)
    *   which is: u32 volume-id, u32 node-id, u32 unique-num
    * Each file has an attribute struct: very similar to inode
    *
    * Typ sequence of calls to podfuk from coda:
    * file read: access(), open(), close()
    *    (the read() is done through the local file)
    * dir listing: access(), open(), lookup(), access(), close()
    * file write: lookup(file), access(parent), create(file), getattr(),
    *    open(), close(), setattr()
    ...
    /* Leave this in place - this is here so that code still is valid
    Makefile. */
    #if 0
    endif
    #endif

Scary.

See http://atrey.karlin.mff.cuni.cz/~pavel/podfuk/podfuk.html for more
information; be sure to have a look at some of the stuff this guy is
doing.

[1] : Why?  Why not?
-- 
____  
\ _/__ ``When the RNG hands you a lemon, #apply it and
 \X  /   see if you can make invisible ink or something.''
   \/      -- Joel Gluth on rec.games.roguelike.nethack

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