Re: zfs support in makefs

On Thu, May 19, 2022 at 01:36:25PM -0400, Allan Jude wrote:
> 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:
> >> https://github.com/freebsd/poudriere/blob/master/src/share/poudriere/image_zfs.sh#L79
> >>
> >> 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.

Sadly -O is taken in makefs.

> 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.

One solution would be to allow the same fs=foo: to be specified multiple
times (I've not checked if the current code allows this) to add options
instead of having a separator.  That does make the command line even more
clunky though.

-- Brooks