ramdisk-zfsroot: pool detection and configurable boot fs

[NetBSD%jornane.no@localhost]

I just tried installing NetBSD 11.0 with Root on ZFS using the guide on 
the wiki[1].  It worked like a charm.  I diverted a little bit from the 
guide, which didn't seem a problem, specifically I used a different disk 
for ZFS.

A problem I ran into though, was that the zfsroot.rc script has not been 
updated for a while, and it requires hardcoded values for the ZFS pool 
and the rootfs (rpool/ROOT).  I made some changes to this script, so 
that it will probe for ZFS pools and check if they have a rootfs 
property set.  I kept it backwards compatible with the current script, 
by always attempting if a ROOT filesystem is available.

Unfortunately, I was unable to build the ramdisk myself.  The guide [1] 
speaks of a program called nbmake-amd64, which I wasn't able to find any 
reference to online.  When trying my best with normal make it stopped 
right away on missing ../../compat/exec.mk, I didn't pursue a fix here.

Instead, I downloaded the current ramdisk, mounted it using vndconfig 
and replaced the etc/rc script in it and *renamed* altroot to zfsroot. 
After that, I was able to reboot into my differently-named ZFS pool, 
setting the filesystem marked as bootfs as the root filesystem.

I've attached the updated rc script, as well as a proposed patch, even 
though I was not able to test the patch due to not being able to build 
the ramdisk.

[1] https://wiki.netbsd.org/root_on_zfs/

--
Jørn Åne

#/bin/sh
#
#       $NetBSD: zfsroot.rc,v 2.0 2026/08/17 05:43:18 jordej Exp $

# Assumption - boot.cfg loads this ramdisk.
# Assumption - The needed kernel modules: solaris and zfs; are either on this
#              ramdisk OR loaded by boot.cfg.
#              Finding the correct dev node to mount to get them is too magic.
# Assumption - NetBSD cannot build and distribute a kernel with ZFS builtin.
# Assumption - One of the available ZFS filesystems has a bootfs property set.
# Assumption - If none of the ZFS filesystems has a bootfs property set,
#              it's because version 1.5 of this rc script assumed rpool/ROOT
#              as root filesystem so we'll try using ROOT as the bootfs.

# Setup some stuff in case things go south and we drop to the shell
export HOME=/
export PATH=/sbin:/bin:/usr/sbin:/usr/bin
umask 022

bootfs=
pools="$(/sbin/zpool list -Honame)
$(/sbin/zpool import | /usr/bin/sed -ne'/^ *pool: / s/^.*: //p')"
echo "zfsroot: Pools found: " $pools >&2
for pool in $pools
do
	echo "zfsroot: $pool: Importing readonly" >&2
	/sbin/zpool export "$pool" 2>/dev/null >&2
	/sbin/zpool import -o readonly -o cachefile=none -f -N "$pool"
	bootfs="$(/sbin/zpool get -Hovalue bootfs "$pool")"
	[ '-' = "$bootfs" ] && bootfs="$(/sbin/zfs get -Hovalue name "$pool/ROOT")"
	[ -n "$bootfs" ] && break

	echo "zfsroot: $pool: missing bootfs property" >&2
	/sbin/zpool export "$pool"
done

if [ -z "$bootfs" ]
then
	echo "zfsroot: No suitable ZFS pool found" >&2
	exit 2
fi

echo "zfsroot: $pool: Found bootfs: $bootfs" >&2
echo "zfsroot: $pool: Importing read/write" >&2
/sbin/zpool export "$pool"
/sbin/zpool import -f -N -o cachefile=none "$pool"

echo "zfsroot: $pool: Mounting $bootfs to /zfsroot" >&2
/sbin/zfs set mountpoint=legacy "$bootfs"
/bin/mkdir -p /zfsroot
/sbin/mount -t zfs "$bootfs" /zfsroot

/sbin/sysctl -w init.root=/zfsroot

From fd8c43822f710bda0f310a66f191a8fdd2fe7d4d Mon Sep 17 00:00:00 2001
From: jornane <NetBSD%jornane.no@localhost>
Date: Mon, 17 Aug 2026 07:43:18 +0200
Subject: [PATCH] zfsroot: ZFS pool detection and configurable boot fs

Iterate over all available ZFS pools and choose the first that has set a
bootfs property on the pool.  This allows users to set which filesystem
they want to use as their root filesystem, in a similar fashin that
other operating systems use for ZFS.  A fallback still explicitly checks
for a filesystem named ROOT, and will use that if no bootfs was set.
Any ZFS pool that contains neither the bootfs property, nor a filesystem
with the name ROOT, is considered unbootable, and is skipped over.
---
 distrib/common/list.zfsroot  |  6 ++--
 distrib/common/mtree.zfsroot |  3 +-
 distrib/common/zfsroot.rc    | 53 ++++++++++++++++++++++++++----------
 3 files changed, 43 insertions(+), 19 deletions(-)

diff --git a/distrib/common/list.zfsroot b/distrib/common/list.zfsroot
index 9b6fb81b7b64..b6f583509f9c 100644
--- a/distrib/common/list.zfsroot
+++ b/distrib/common/list.zfsroot
@@ -9,7 +9,7 @@ PROG	sbin/zpool
 LINK	sbin/zfs sbin/mount_zfs
 ARGVLN	zfs mount_zfs
 
-# We need sysctl to set init.root=/altroot
+# We need sysctl to set init.root=/zfsroot
 PROG	sbin/sysctl
 
 # We need modload as we cannot build CDDL modules in the kernel
@@ -31,5 +31,5 @@ LIBS	-lzfs_core
 COPY	${NETBSDSRCDIR}/distrib/common/zfsroot.rc etc/rc
 
 # Make modules and firmware images available
-SYMLINK	altroot/stand stand
-SYMLINK	altroot/libdata libdata
+SYMLINK	zfsroot/stand stand
+SYMLINK	zfsroot/libdata libdata
diff --git a/distrib/common/mtree.zfsroot b/distrib/common/mtree.zfsroot
index be040287c1e4..2d1412628661 100644
--- a/distrib/common/mtree.zfsroot
+++ b/distrib/common/mtree.zfsroot
@@ -1,5 +1,4 @@
 #	$NetBSD: mtree.zfsroot,v 1.3 2020/02/23 10:51:12 roy Exp $
 
 .
-./altroot
-./rpool
+./zfsroot
diff --git a/distrib/common/zfsroot.rc b/distrib/common/zfsroot.rc
index 03183464e75f..9427b1de0761 100644
--- a/distrib/common/zfsroot.rc
+++ b/distrib/common/zfsroot.rc
@@ -1,28 +1,53 @@
 #/bin/sh
 #
-#	$NetBSD: zfsroot.rc,v 1.5 2020/04/14 12:14:59 roy Exp $
+#       $NetBSD: zfsroot.rc,v 2.0 2026/08/17 05:43:18 jordej Exp $
 
 # Assumption - boot.cfg loads this ramdisk.
 # Assumption - The needed kernel modules: solaris and zfs; are either on this
 #              ramdisk OR loaded by boot.cfg.
 #              Finding the correct dev node to mount to get them is too magic.
-#              NetBSD cannot build and distribute a kernel with ZFS builtin.
-# Assumption - the root pool is set to legacy mount.
+# Assumption - NetBSD cannot build and distribute a kernel with ZFS builtin.
+# Assumption - One of the available ZFS filesystems has a bootfs property set.
+# Assumption - If none of the ZFS filesystems has a bootfs property set,
+#              it's because version 1.5 of this rc script assumed rpool/ROOT
+#              as root filesystem so we'll try using ROOT as the bootfs.
 
-# Configurable - define the ZFS root pool and ROOT.
-# XXX Can these be set in boot.cfg?
-rpool=rpool
-rroot=ROOT
-
-# Setup some stuff incase things go south and we drop to the shell
+# Setup some stuff in case things go south and we drop to the shell
 export HOME=/
 export PATH=/sbin:/bin:/usr/sbin:/usr/bin
 umask 022
 
-echo "Importing $rpool"
-/sbin/zpool import -f -N "$rpool"
+bootfs=
+pools="$(/sbin/zpool list -Honame)
+$(/sbin/zpool import | /usr/bin/sed -ne'/^ *pool: / s/^.*: //p')"
+echo "zfsroot: Pools found: " $pools >&2
+for pool in $pools
+do
+	echo "zfsroot: $pool: Importing readonly" >&2
+	/sbin/zpool export "$pool" 2>/dev/null >&2
+	/sbin/zpool import -o readonly -o cachefile=none -f -N "$pool"
+	bootfs="$(/sbin/zpool get -Hovalue bootfs "$pool")"
+	[ '-' = "$bootfs" ] && bootfs="$(/sbin/zfs get -Hovalue name "$pool/ROOT")"
+	[ -n "$bootfs" ] && break
+
+	echo "zfsroot: $pool: missing bootfs property" >&2
+	/sbin/zpool export "$pool"
+done
+
+if [ -z "$bootfs" ]
+then
+	echo "zfsroot: No suitable ZFS pool found" >&2
+	exit 2
+fi
+
+echo "zfsroot: $pool: Found bootfs: $bootfs" >&2
+echo "zfsroot: $pool: Importing read/write" >&2
+/sbin/zpool export "$pool"
+/sbin/zpool import -f -N -o cachefile=none "$pool"
 
-echo "Mounting $rpool/$rroot to /altroot"
-/sbin/mount -t zfs "$rpool/$rroot" /altroot;
+echo "zfsroot: $pool: Mounting $bootfs to /zfsroot" >&2
+/sbin/zfs set mountpoint=legacy "$bootfs"
+/bin/mkdir -p /zfsroot
+/sbin/mount -t zfs "$bootfs" /zfsroot
 
-/sbin/sysctl -w init.root=/altroot
+/sbin/sysctl -w init.root=/zfsroot
-- 
2.55.0