Re: resize_ffs and ufs2

[David Holland <dholland-tech%netbsd.org@localhost>]

On Mon, Jul 03, 2017 at 09:15:54AM -0400, Chris Humphries wrote:
 > Working with coypu and interested in kernel development, with filesystems
 >  and data storage in particular, I was pointed to resize_ffs and shrinking
 > ufs2 support (PR #44205 and in src/sbin/resize_ffs/TODO).
 > 
 > My question is before I get started, are there things a newbie like me
 > should know before I boldly plow into the code of ufs2 and resize_ffs
 > deeper? Want to be sure I at least check if there is tribal or expert
 > knowledge on the challenges of this task before rediscovering the wheel.

I have no idea what's wrong with resize_ffs shrinking ffsv2, but one
of the significant differences between ffsv1 and ffsv2 is that in
ffsv2 inodes are not zeroed out in advance by newfs; instead there's a
thing that keeps track of which ones have been zeroed and which ones
still need to be. Manipulating that correctly was what was missing
from growing ffsv2 volumes at one point.

Also mind PR 44204, but it is probably not closely related.

-- 
David A. Holland
dholland%netbsd.org@localhost