On Thu, 10 Aug 1995 09:58:31 -0700 (PDT) 
 wrstuden@loki.stanford.edu (Bill Studenmund) wrote:

[ I trimmed the long Cc: list. --thorpej ]

 > My first thought was to build a fake disklabel, use it to read whatever
 > needs to be read to get a real disklabel, throw out the fake disklabel as
 > it's not needed anymore, and make the real one.

This already happens ... Say, for example, I install a band-new disk on 
my hp380 ... pretend it's sd4 ... the process I usually go though is:

	# cd /etc/disklabels
	# disklabel sd4 > sd4.label (grabs fake in-core copy)
	# vi sd4.label
	  [ . . . edit label . . . ]
	# disklabel -r -R sd4 sd4.label
	# newfs /dev/rsd4[whatever]

Note that when you update the on-disk copy, the in-core copy is updated 
as well.

 > Ah, but did you (or the kernel secretly behind your back) use dos
 > partitioning software/conventions? You (or someone else) described how
 > the i386 port has `c' as the NetBSD part of the disk, and `d' the whole
 > disk. To me, this means that your disk _can_ have DOS stuff in it. As I
 > understand it, if you take your all-NetBSD disks to a DOS machine,
 > the DOS machine will know that the drive is formated, and that it is
 > full of non-DOS partitions. Granted it will have no clue as to what to
 > do with the non-DOS stuff, but DOS will know not to step on the data.

Well, of course ... I'm not really sure I see your point, though.  (I 
mean, that's the whole point of `d' is the whole disk, and `c' is 
NetBSD's portion...)

 > Oops! Take a step back. Is there a difference ON DISK? Looking at just
 > the disk, can't we tell the difference between formats between various
 > OS's?

Ummm ... sort of ... You can just read what you think is the right place 
and look for the right magic numbers, providing the on-disk format that 
you're reading provides such a mechanism for validating the label.  If 
not, then you're just second-guessing.

 > If all these patterns are different, then we can look for each one in
 > turn.  If we find one, we know the partitioning scheme in use on the
 > disk. We then look to the port for that machine and ask it to read the
 > disklabel, as it already understands this partitioning scheme.

That's what my code did ... it gave preference to the port's `native' 
disklabel format, and then jumped though function pointers looking though 
the other formats until it didn't fail anymore.  If none of them 
succeeded, `no disk label' was reported and a fake label generated.

 > Though you do bring up one interesting question. What in the system REALLY
 > cares where the whole disk gets shoved? Isn't it just convention?

Lots of things use RAW_PART ... see the MI SCSI code for examples ...

--------------------------------------------------------------------------
Jason R. Thorpe                                       thorpej@nas.nasa.gov
NASA Ames Research Center                               Home: 408.866.1912
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