Re: zfs support in makefs

From: Allan Jude <>
Date: Thu, 19 May 2022 17:36:25 UTC
On 5/18/2022 7:04 PM, Brooks Davis wrote:
> On Wed, May 18, 2022 at 03:03:17PM -0400, Mark Johnston wrote:
>> Hi,
>> For the past little while I've been working on ZFS support in makefs(8).
>> At this point I'm able to create a bootable FreeBSD VM image, using the
>> standard FreeBSD ZFS layout, and run through the regression test suite
>> in bhyve.  I've also been able to create and boot an EC2 AMI.
> Very cool!
>> === Interface ===
>> Creating a pool with a single dataset is easy:
>> $ makefs -t zfs -s 10g -o poolname=test ./zfs.img /path/to/input
>> Upon importing such a pool, you'll get a dataset named "test" mounted at
>> /test containing everything under /path/to/input.
>> It's possible to set properties on the root dataset:
>> $ makefs -t zfs -s 10g -o poolname=test -o fs=test:setuid=off:atime=on ./zfs.img /path/to/input
>> It's also possible to create additional datasets:
>> $ makefs -t zfs -s 10g -o poolname=test -o fs=test/ds1:mountpoint=/test/dir1 ./zfs.img /path/to/input
>> The parameter syntax is
>> "-o fs=<dataset name>[:<prop1>=<val1>[:<prop2>=<val2>[:...]]]".  Only a
>> few properties are supported, at least for now.
>> Dataset mountpoints behave the same as they would if created with the
>> standard ZFS tools.  So by default the root dataset's mountpoint is
>> /test, test/ds1's mountpoint is /test/ds1, etc..  If a dataset overrides
>> its default mountpoint, its children inherit that mountpoint.
>> makefs builds the output filesystem using a single input directory tree.
>> Thus, makefs -t zfs requires that at least one of the dataset's
>> mountpoints map to /path/to/input; that is, there is a "root" mount
>> point.
>> The -o rootpath parameter defines this root mount point.  By default it's
>> "/<poolname>".  All datasets in the pool must have their mountpoints
>> under this path, and one dataset's mountpoint must be equal to this
>> path.  To build bootable images, one sets -o rootpath=/.
>> Putting it all together, one can build a image using the standard layout
>> with an invocation like this:
>> makefs -t zfs -o poolname=zroot -s 20g -o rootpath=/ -o bootfs=zroot/ROOT/default \
>>      -o fs=zroot:canmount=off:mountpoint=none \
>>      -o fs=zroot/ROOT:mountpoint=none \
>>      -o fs=zroot/ROOT/default:mountpoint=/ \
>>      -o fs=zroot/tmp:mountpoint=/tmp:exec=on:setuid=off \
>>      -o fs=zroot/usr:mountpoint=/usr:canmount=off \
>>      -o fs=zroot/usr/home \
>>      -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 \
>>      ${HOME}/tmp/zfs.img ${HOME}/tmp/world
>> I'll admit this is somewhat clunky, but it doesn't seem worse than what
>> we have to do otherwise, see poudriere-image for example:
>> What do folks think of this interface?  Is there anything missing, or
>> anything that doesn't make sense?
> I find it slightly confusing that -o options have a default namespace of
> pool options unless they have an fs=*: prefix, but making users type
> "pool:" for other options doesn't seem to make sense so this is probably
> the best solution.
> The density of data in the filesystem specification does suggest that
> someone might want to create a UCL config file format eventually, but
> what's here already seems entirely workable.
> -- Brooks

In normal `zpool create` they use -o for pool properties, and -O for 
dataset properties for the root dataset. I wonder if we might also want 
-o poolprop=value and -O zroot/var:mountpoint=/var:canmount=off

just to avoid the conceptual collision of those 2 different items.

One other possible issue: dataset properties can have a : in them, for 
user-defined properties. Do we maybe want to use a , to separate them 
instead? Although values can contain ,'s (the sharenfs property often 
does), so that probably doesn't work either.

Allan Jude