[Bug 282832] makefs zfs creates images with the same guid

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=282832

--- Comment #6 from Pat Maddox <pat@patmaddox.com> ---
My root pool is copied from release / our prior convo:

    makefs -t zfs -s 20g \
           -o poolname=zroot -o bootfs=zroot/ROOT/default -o rootpath=/ \
           -o fs=zroot\;mountpoint=none \
           -o fs=zroot/ROOT\;mountpoint=none \
           -o fs=zroot/ROOT/default\;mountpoint=/ \
           -o fs=zroot/home\;mountpoint=/home \
           -o fs=zroot/tmp\;mountpoint=/tmp\;exec=on\;setuid=off \
           -o fs=zroot/usr\;mountpoint=/usr\;canmount=off \
           -o fs=zroot/usr/ports\;setuid=off \
           -o fs=zroot/usr/src \
           -o fs=zroot/usr/obj \
           -o fs=zroot/var\;mountpoint=/var\;canmount=off \
           -o fs=zroot/var/audit\;setuid=off\;exec=off \
           -o fs=zroot/var/crash\;setuid=off\;exec=off \
           -o fs=zroot/var/log\;setuid=off\;exec=off \
           -o fs=zroot/var/mail\;atime=on \
           -o fs=zroot/var/tmp\;setuid=off \
           ${outfileroot} ${rootdir}

and the data pool is another typical invocation:

    makefs -t zfs -s 100m \
           -o poolname=zdata -o rootpath=/ \
           -o fs=zdata\;mountpoint=/\;canmount=noauto \
           -o fs=zdata/usr\;mountpoint=/usr\;canmount=off \
           -o fs=zdata/usr/local\;canmount=off \
           -o fs=zdata/usr/local/poudriere \
           ${BUILDDIR}/zdata.zfs ${BUILDDIR}/data

-----

> the root pool should be reguid'ed on first boot anyway.  The official VM images configure this automatically (they set zpool_reguid=zroot in /etc/rc.conf)

Good to know, I will check that out. I would kind of expect it to not work,
because I think the boot process doesn't even make it that far as I showed
above. I'll try it out and report back though.

So I think it may be worth providing a way to 1) randomize the guid on creation
and/or 2) seed the RNG on creation.

Extend this to a third disk: I have one root pool, one read-only pool with a
dataset, and a third writable pool that contains long-lived data. I need all of
these to have different GUIDs.

The reason I may want to seed the RNG is because if I replace the root pool, I
want the VM to think it's the same. From the VM standpoint, it's like I
exported the pool, imported it to another host, did some stuff on it, and
imported it back on the VM. I happen to be reconstructing the disk via code,
but no reason the VM needs to know that.

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