DragonFlyBSD

This is v1 of the new Device Mapper target dm-delay.
https://www.dragonflybsd.org/~tkusumi/diff/0001-sys-dev-disk-dm-Add-dm-delay-target-v1.patch

dm-delay has existed in Linux kernel,
and this is the dm-delay target for DragonFly based on
the Device Mapper code originally ported from NetBSD.

1. newfs_hammer -L TEST /dev/da3 > /dev/null
2. mount_hammer /dev/da3 /HAMMER
3. hammer volume-list /HAMMER
   /dev/da3
4. cd /HAMMER
5. time git clone /usr/local/src/dragonfly
   Cloning into 'dragonfly'...
   done.
   Checking out files: 100% (34298/34298), done.
   git clone /usr/local/src/dragonfly 2.88s user 4.26s system 48% cpu 14.577 total

1. newfs_hammer -L TEST /dev/da3 > /dev/null
2. kldload dm
3. dmsetup create delay1 --table '0 234436482 delay /dev/da3 0 10 /dev/da3 0 10'
4. dmsetup ls --tree
   delay1 (255:504430599)
   `- (0:504430623)
5. mount_hammer /dev/mapper/delay1 /HAMMER
6. hammer volume-list /HAMMER
   /dev/mapper/delay1
7. cd /HAMMER
8. time git clone /usr/local/src/dragonfly
   Cloning into 'dragonfly'...
   done.
   Checking out files: 100% (34298/34298), done.
   git clone /usr/local/src/dragonfly 2.78s user 3.91s system 5% cpu 2:05.05 total