Re: [linuxdc-dev] VMU filesystem question

[David W. <dav...@ia...>]

> What is a "webpal"?

It's an early era web browsing set top box.  They weren't tied to a
particular ISP, so they sold for full price--$400(USD).  They didn't
sell well and now there a ton of them available for almost nothing.
I paid $8(USD) each for mine.

The box has a cirrus CL-PS7500FE which is an arm 7 core processor 
running at 40MHz.  There is one DRAM 72 pin SIMM slot and one FLASH
72 pin SIMM slot.  It comes with 4MB and 1MB resprectively.  You can
put 2k refresh simms in it.  Mine has 32MB and there is a simple mod
to allow 4k page refresh simms, as well.  It has sound out, parallel, 
PS/2 mouse & KB, and VGA out on the back pannel.  It's also got one 
semi-functional ISA slot internally.  On the front is the IR sensor, 
three LEDs and a smart card slot.  Internally, it has an IDE connector.
You can graft on a 5V connector, a short IDE cable and a 3.5" to 2.5"
IDE adapter and you can stuff in a laptop HD of your choice.

So, after some soldering and a lot of software hacking, one is left with
a little ARM box running Linux.  (Oh, forgot, it has composite and S-video
out as well--same content as the VGA out.)

Cute little box.  I'm thinking of grafting a GPS receiver board (Motorola
OnCore GT+) into it with a small patch antenna and making an NNTP server
for my house/ham shack.

> > Since you're the author of the fs in question and since I've got you. :)
> > Could you say just what it is you want the vmufs to do?  The two ways
> > I could see it looking and being useful are:
> > 1: full blown filesystem with metadata exposed as files (copyable, tarable,
> > editable, etc.)
> > 2: just able to 'stash' a file on it and get it back--don't need to look
> > at or edit the DC files.  Also, keep the DC from choking on the files
> > we produce.
> 
> The rea aim, such as there was one, was to allow game players to swap files 
> easily, I suppose. But it's a toy, so there are other things - eg I thought 
> of hosting apache off one!

:)  Okay, then to satisfy that, how about just making the first block of
the file (as seen by the VFS side) completely fake and containing the 'hidden'
directory info.  On write it gets stuffed into the directory entry.  It'll
also tell the vmufs how to allocate the file--most everyone will write the
file block by block from the beginning, so you'll have the data to start
with.

Does that solve things or are there other issues I'm missing?

> > There is always #3 which is to stop all of this and just develop a nice
> > suite of userspace tools like mtools (for MSDOS filesystems).  But, I
> > assumed that we had already passed that fork in the road by talking
> > about a FS to start with. :)

> Well I have a working fs now - albeit it (mainly, it also deletes) being a 
> read-only one. As for the options I am not sure what to do now...I need to 
> give it some more thought and decide whether to continue pusuing the rw 
> option for the fs or just stop where we are now...

My simple solution--above--does make us Linux users unable to simply write
*our* DC-unaware files to it as the first block will get trashed and the
stuff we though we wrote will put some junk in the directory entry.  Of 
course, you could get 'clever' and look at the first block and see if the
unused chunks were left alone and if so, assume it's a proper DC file,
otherwise assume it's a native Linux file and fake some safe directory 
info.

It just doesn't seem like we can have both.

But wait!  Inspiration strikes.  Okay, a hybrid.  From the root of the fs,
there is a directory called 'NativeDC' and it contains the first-block-
faked stuff from above.  There's another directory (seen from the VFS)
caled 'NativeLinux' and it contains the unix style files.  Here's the
trick.  The Linux files are stored *on the VMU* as one file with some
stock DC compatible header.  So, basically the complete Linux filesystem
gets hidden on one DC file on the VMU.  

The cool thing about that is we can copy the DC files with unix--from/to
a VMU or other device--and all the special info gets preserved.  Also,
we can have normal unix stuff hidden in out one little file--permissions,
directories, etc.  *And* the DC browser can copy our whole FS from one
VMU to another because the header/directory entry it's hidden in looks
legit.

I'm typeing this fast, so I might not be making sense.  Let me know and
I'll slow down and get more detailed.  I think this will work and it'll
do *everything* we want. :)

Cheers,
David