Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!visdc!jiii
From: jiii@visdc.UUCP (John E Van Deusen III)
Newsgroups: comp.unix.i386
Subject: Re: Mylex SCSI Controller, 16550A UARTS
Message-ID: <655@visdc.UUCP>
Date: 11 Oct 89 16:37:50 GMT
References: <111016@nstar.UUCP> <707@fiver.UUCP> <2834NU013809@NDSUVM1> <6075@tekgvs.LABS.TEK.COM> <982@crdos1.crd.ge.COM>
Reply-To: jiii@visdc.UUCP (John E Van Deusen III)
Organization: VI Software Development, Boise, Idaho
Lines: 27

In article <982@crdos1.crd.ge.COM> davidsen@crdos1.UUCP (bill davidsen)
writes:
> ... writing to a raw device is a good way to leave a very dead
> filesystem.

It is a good idea never to write over the VFIB information stored in
block 0 of a hard disk.  It might require invoking some very obscure
utility to get it back; something more obscure than mkfs, possibly
involving a lengthy and totally destructive disk format.

When you make a file system you specify a parameter BLOCKS that is the
desired size of the file system.  If the amount specified is less than
the space actually available on the device, then the extra space can be
used for raw I/O.  Of course, there is no requirement to have any file
system on the device at all, thus making the entire device, except for
block zero, available.

All this requires that the program doing raw I/O is smart enough to
offset any useful information stored on the the device.  Anything like
myprog > /dev/smd0.0 is, as Mr. Davidsen says, certain doom.  That said,
I will bet that at least one person reading this has a special file in
/dev, associated with a file system, that is writable (readable) by
everyone!
--
John E Van Deusen III, PO Box 9283, Boise, ID  83707, (208) 343-1865

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