Re: Proposal to enable WAPBL by default for 10.0

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Thu, 23 Jul 2020 08:43:04 -0400
> From: Greg Troxel <gdt%lexort.com@localhost>
> 
> Taylor R Campbell <riastradh%NetBSD.org@localhost> writes:
> 
> [lots of good points, no disagreement]
> 
> If /etc/master.passwd is ending up with junk, that's a clue that code
> that updates it isn't doing the write secondary file, fysnc it, rename,
> approach.  As I understand it with POSIX filesystems you have to do that
> because there is no guarantee on open/write/close that you'll have one
> or the other.  Even with zfs, you could have done write on the first
> half and not the second, so I think you still need this.

Yes, that sounds right and we should fix whatever writes
/etc/master.passwd.  There's no way it's performance-critical so it
should be fine to add fsync.

> > work...which is why I used to use ffs+sync on my laptop, and these
> > days I avoid ffs altogether in favour of zfs and lfs, except on
> > install images written to USB media.)
> 
> Do you find that lfs is 100% solid now (in 9-stable, or current)?  I
> have seen fixes and never really been sure.

No -- but the main point is that when anything goes wrong and the
system crashes or power fails, it doesn't leave garbage data at the
end of files like ffs does, leading, e.g., to spectacularly corrupted
CVS trees.

I fixed a lot of deadlocks in lfs in HEAD earlier this year.  Haven't
yet pulled them up to 9 because there was one major deadlock remaining
that I had an unsatisfactory fix for, and I haven't gotten around to
testing a better fix yet.