Re: NetBSD resize_ffs SoC project

[der Mouse <mouse%Rodents.Montreal.QC.CA@localhost>]

>> 2) online filesystem shrinking and growing.  This needs major
>> rewrite of resize_ffs and add support to FFS driver in kernel.
> I don't really think that *online* shrinking is important.

I'm not sure.  It projbably is not worth the effort it would take, but
it sure would be nice to have.

> I am not even sure that shrinking is possible without limitations as
> inodes are spread over the disk and you can't remove a cylinder group
> without changing inode numbers, can you?

Only if none of the cg's inodes happen to be used, something that is
unlikely unless the filesystem is very low in inodes-used.

Live shrinking would be a fairly elaborate thing.  resize_ffs's shrink
code involves reading every directory in the filesystem to rewrite
directory entries referring to moved inodes (in theory this could be
done more efficiently if all the moved inodes are directories, but that
is sufficiently unlikely I didn't bother even checking for it).  At
least some of that would need to be moved into the kernel.

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