I've brought Kirk McKusick's trickle sync + FFS soft update code into
the main tree. It has had some moderate to heavy testing over the
last month. I'm currently using it on the /usr filesystem and the
filesystem containing all my sources on my main NetBSD development
machine, and did not have a problem since I fixed the last known
bug (2.5 weeks ago).

To use it, do the following:

1. Update your sources.
2. Compile a new kernel with "options SOFTDEP" in your kernel config file.
3. Run the new kernel.
4. Install the new include files from sys/sys (i.e. at least do
   cd /usr/src/sys ; make includes). To be safe, just install them all
   (cd /usr/src ; make includes)
5. At least recompile libc, sbin/mount, sbin/fsck_ffs, sbin/tunefs, and
   install them.
6. Run "tunefs -n enable /dev/rXd0x" to enable soft updates on the
   filesystem(s) of your choice.
7. Remove "update=YES" from your /etc/rc.conf file. update(8) is no longer
   needed. Its work is now done in a more sophisticated way by a kernel
   thread.
8. Reboot
9. Have fun testing.

If you have any problems, please send PRs, or mail me, with as much
detail as you can gather. Again, I haven't had any problem for a
while now, and am running it on critical filesystems.

- Frank