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From: jca@pnet01.cts.com (John C. Archambeau)
Newsgroups: comp.os.minix
Subject: Re: Minix reading/writing non-Minix file systems (SunOS?)
Message-ID: <4912@crash.cts.com>
Date: 11 Oct 90 01:56:04 GMT
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Organization: People-Net [pnet01], El Cajon CA
Lines: 75

pezely@cis.udel.edu (Daniel Pezely) writes:
>Wouldn't it be convienent if machines running Minix, which had a file
>system on a SCSI drive, could read Berkeley (or even SunOS) file systems?

First of all, BSD and SunOS are the same animals with respect to file system
structure.  All SunOS is basically is BSD Unix 4.3 with some of Sun's code
added.  All you basically need is a BSD 4.2 file system module to replace
Minix's fs module, but then of course, you're running into a multiple file
system problem.  What if I have one Minix file system on this Seagate ST251
a BSD 4.2 file system on this CDC Wren IV hooked to my Adaptec AHA 1542B? 
You'd need a 'smart' file system module to determine the file system type.  I
suppose this wouldn't be too difficult, but remember the BSD 4.2 file system
was designed with some performance issues in mind.  The Minix file system was
designed to get the point across about general Unix file system structure with
the common denominators being the superblock, free list, and inode table.

One, the BSD file system has superblock backups at a spaced interval, the
Minix file system only has one superblock per file system.

So you see, you have some radical FS implementation changes.

>First of all, would that be legal?  (Assuming the site had a BSD,
>SunOS, AT&T, etc license, of course.)

I don't see any problems providing you don't use any AT&T, BSD, or Sun code to
accomplish the job.  Sure, the data structures are the same, but I know that
the authors of the DOS utilities for Minix didn't pay a license to MicroSoft
to write the DOS file system utilities.
 
>But more importantly, how difficult would that be to pull off?
 
I have a book here on the design of BSD Unix, but I haven't had a chance to
read it, but I do know that the file system module would have to be rewritten
to handle both the BSD 4.2 file system and the Minix file system.  Of course,
then there's a similiar argument if you want to do it for Xenix and Unix
System V file systems.  Where do you draw the line?  Where will Minix stop? 
Or do you want to make a universal file system read utility that will decipher
the file system you have on a given disk and allow you to read any given file
system from a floppy?  See my point?

>It would be nice to be able to just take an external drive off of a
>SparcStation and slap it on, say, a 386, then use it and put it back.
 
What would be the point in taking a drive off the SPARCstation and putting it
back on?  It's a novel idea for the Minix wish list, but I have yet to see a
Sun customer that I've installed a Sun for 'take a drive off the Sun and put
it back later.'  Are you sure you don't want a tape driver that can read
QIC-24 tapes instead?  Personally, the only time I take a drive on and off a
machine is to test it, otherwise the drive stays where it belongs.  Don't mean
to chastise you or anything, but your idea of why Minix should be able to
read/write to BSD 4.2 file systems doesn't quite make sense to me in
application.  For floppy disks and removable media drives I can understand,
but hard drives just aren't mean to be taken on and off an system on the fly.

See my meaning here?
 
>OK, for those worried about legalities, how about doing it to read dos
>hard disks?  What would the scale of such a task be?

My understanding is that Minix already handles MS-DOS 3.30 file systems just
fine.  Or has this been worked out fully yet?  I know that I had no problems
in reading DOS 3.30 primary partitions when I ran Minix 1.3 awhile back on my
286 box.  Right now I'm just waiting to see Minix 386 to become a bit more
solid before I allocate hard drive space for it and tinker around with it.
 
     // JCA

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