News Group Posts

divvy filesystem divvy table mkfs

Newsgroups: comp.unix.sco.misc
From: Bela Lubkin <belal@sco.com>
Subject: Re: divvy
Cc: Lodo Nicolino <greenflag@libero.it>
Date: Fri, 28 Sep 2001 22:16:53 GMT
Message-ID: <20010928151653.H5148@mammoth.ca.sco.com> 
References: <3BB4789B.88D043D2@libero.it> 

Lodo Nicolino wrote:

> I would like to know where divvy write the information. Ex: block,
> filesystem name etc

Please see these Technical Articles:

  http://aplawrence.com/cgi-bin/ta.pl?arg=106296
  http://aplawrence.com/cgi-bin/ta.pl?arg=104384
  http://aplawrence.com/cgi-bin/ta.pl?arg=107180

I'll add one thing, which is probably covered in one of those articles
but worth mentioning again: what you see when you run `divvy` is
actually a compendium of information compiled from three different
sources.

First, there's the divvy table on the partition.  This tells us the
start and end block numbers of each division.

Second, `divvy` searches the /dev directory on the active root
filesystem, looking for device nodes whose major/minor numbers
correspond to those of the various divisions being looked at.  For
instance, on an OSR5 root partition, /dev/root is usually device 1/42.
When you run divvy it does not find the string "root" in the division
table.  It computes that the device number of division #2 on this
partition would be 1/42.  Then it looks in /dev, notices /dev/root is
1/42, and displays "root" in the on-screen table.  This is significant
because if you boot off a recovery floppy, it will only know the device
names of your divisions if their device nodes have been copied to the
floppy.

Third, it actually _reads_ the first few K bytes of each of the
divisions in order to comment on what _type_ of data is present.  In the
case of 1/42, it opens /dev/root, reads a bit, and (in most cases)
determines that it's an HTFS filesystem.  So it displays "HTFS".  It
reads /dev/boot and learns that it's "EAFS"; it reads /dev/swap and
doesn't recognize it as any particular filesystem type, so displays "NON
FS".

When you _change_ division start/end points, divvy writes the new
information to the division table at the beginning of the partition.

When you change division _names_, divvy deletes /dev/oldname and
/dev/roldname and creates /dev/newname, /dev/rnewname with the right
device numbers.

When you "change the type" of a division in divvy, it has no effect.
Only when you also tell it to "create a new filesystem" does it do
anything.  Then, when you tell it to act on your wishes (i.e. when you
q[uit], i[nstall]), it runs `mkfs` to create a filesystem of the
requested type.  Assuming that succeeds, next time you enter divvy it
will show the new type.  (This of course destroys the previous contents
of the filesystem; as would changing a division's start/end points.  Be
careful while experimenting with divvy!)

>Bela<
 

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