Re: Can't change partition table anymore

On Mon, 2005-04-04 at 07:28 +0400, Andrey Chernov wrote:
> BTW, the trick with kern.geom.debugflags=16 works and I put it permanently 
> in my sysctl.conf. Could you please make it ON by default or make a 
> warning at least?

I actually agree with this.  It's so frustrating to not be able to do
what you want to do as root.

Consider the following two examples:

- Freshly installed machine, I want to move the root disk to be a GEOM
mirror.  I can't, because gmirror can't open /dev/ad0 for writing, even
though I know the last sectors which it needs to write to are unused.
It can't even be done in single user mode, as / is still mounted.  The
only way to do this seems to be to boot off a fixit CD, with all the
problems that brings with it.  (this issue has been discussed several
times before)

- I have a partition, which I would like to split into two smaller
partitions.  Even though it is unmounted, and it's perfectly safe to do,
I'm prevented from doing it.  Again, it can't be done in single user
mode either.  Back to the fixit CD.

I fully understand why the feature exists, but when it gets in the way
of legitimate system administration then perhaps it should be disabled
by default (or perhaps based on securelevel).  Having to flip bits
clearly labelled "debug" flags doesn't seem to be a good solution.

Maybe the way forward is to make it more intellegent, "hang on, you
can't destroy that partition because this geom is using it".  I 'm not
sure how this could be implemented, I guess another geom method would
have to exists to basically say "somebody wants to make this change, is
it ok with you?" before the write occurs, and the caller either gets
returned success, or something like EROFS if the responsible geom turned
it down.  Only the geom in question can ever know if a particular change
is safe, so it should be up to that to authorise or deny a change.

Or, allow the change, then notify all attached consumers of da0 and say
"hey, something's changed".  Let the consumers pass that down to the
consumers it affects which either respect it (if it can be respected or
if it changes nothing significant) or self-destruct.

I don't know enough about geom to know the best solution, but something
really should be done about it.

Gavin