g_part partition tool -- some logistic questions

[Poul-Henning Kamp]

In message <D63AC737-8D1B-4835-BCC5-52E055A702FF at mac.com>, Marcel Moolenaar wri
tes:

>The first question relates to finding and presenting the right
>devices/providers to the users. What I don't want is present,
>for example, ad0 and ad1 if they are part of a mirror. I'd like
>to present the mirror to the user. The same applies to other
>GEOM classes.
>
>Is there a generic or established way to walk the GEOM tree
>(obtained by geom_gettree()), and find the real or true virtual
>storage providers that takes the hierarchy into account?

There are no providers that are more "real" or "true" than
others, they are all "just" providers.

If you want to add a "desirability" property to the providers,
then I'm all for it, provided you explain up front how you
expect it to actually work.

If you have bsd(mirror(ad0,ad1)), then the BSD parts should
be more desirable than the mirror or the disks.

If on the other hand you have mirror(bsd(ad0),bsd(ad1)), then
the mirror should be more desirable than the bsd's and the disks.

It follows from this that just assigning a desirability to
a class or an instance is not trivial.

In general however, I think we can do a pretty good approximation
to "DWIM" by using the rank property, because in general
people don't stack things up if they don't want to get upwards.

So you may want to try something like pruning everything but
the highest ranking leaf providers in each subtree and see where
that gets you.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.