Make md(4) support GEOM::ident.

[trasz]

Summary

Make md(4) support GEOM::ident. For swap- and malloc-backed disks
it's random; for vnode-backed ones it's based on backing file device
and inode numbers.

[kib]

sys/dev/md/md.c

1301

This allows duplicated idents.

What is the purpose of the field ?

1419

Did you build-tested this on 32bit arches ?

[trasz]

sys/dev/md/md.c

1301

You mean, 32 bits are not enough to guarantee uniqueness?

As for the purpose - in this case (generally: in cases other than vnode) it doesn't serve any purpose. Perhaps I should just remove it for cases other than vnode?

1419

Not yet.

[kib]

sys/dev/md/md.c

1301

I mean that two arc4random() call makes no guarantee about uniqueness of the result.

You add some feature and do not explain its purpose, more, you state that in some cases the feature has no purpose.

[mav]

I don't see a point in reporting random ident strings. Those are normally useful to make things persistent, but random is not a way for that. May be I'd see it more useful to have it user-configurable.

[trasz]

Get rid of random idents; they don't serve any purpose.

[trasz]

Fix tinderbox.