Wow. Okay.
On Mon, 6 Dec 1999, Bruce Evans wrote:
> On Sat, 4 Dec 1999, Matthew Jacob wrote:
>
> > It seems that in the latest running around with things, disklabel -W
> > doesn't seem to quite work, at least on the alpha- it seems to set the
> > label writable, but the next attempt to open the disk sets the label area
> > non-writable again.
>
> It hasn't quite worked for 5 years now (except for additional not workage
I was being polite... :-)
> on alphas). There are layers and layers of bugs and features which
> combine to make it very difficult to write the label sector except in the
> normal way:
> ...
>
> (4) Write protection and i/o snooping of labels is half-intentionally
> broken for i/o to the whole disk slice (e.g., /dev/da0). It can be
> used to work around bugs and features in the write protection and
> snooping. E.g., the only way to clear a label is to write garbage
> over it using the whole disk slice. Writing garbage over it using
> an ordinary slice is prevented by the i/o snooping code.
>
> (5) The whole disk slice was broken for alphas in rev.1.63 of
> subr_diskslice.c, by putting a label on it if the underlying disk
> contains a label. The underlying disk contains a label in the
> "dangerously dedicated case". If there is a label, then it is
> initially write protected, and always snooped on. This closes
> the back door in (4).
>
> > Secondly, how do people feel about having dd(1) use the DIOCWLABEL
> > argument to enable writing the label area of the disk if the output is a
> > disk and there is no offset from zero?
>
> Unwell. The whole disk device (e.g., /dev/da0) is already entirely
> write-enabled and unsnooped. except as in (5). Write protection of
> labels should continue to apply to partitions (e.g., /dev/da0a and
> /dev/da0c) even if the partitions start at offset 0.
The reason I brought this all up is that XX0 access would not work for me.
The disk had a dangerously dedicated label, but I wanted to overwrite the
front of the disk. Impossible. I've noticed this also in the case where
you have slices but want to go to a dangerously dedicated label- no can
do.
Hence a "Well, gee, let's see if disklabel -W will help". Nope.
So, what's the answer about what to do? I sure wouldn't want to leap
in and 'fix' it because I don't have a good feel for the ins and outs
of this stuff here (odd- I usually have a strong sense of knowing
what's right, but this house of cards gives me the creeps).
I have a hacked dd that works for me, but this can't be the right general
solution. Probably if I added my disk tester into the test suites, that
would allow one to force this (although by default the tester I use always
skips label areas).
-matt
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