Date: Thu, 19 May 2022 13:36:25 -0400 From: Allan Jude <allanjude@freebsd.org> To: freebsd-hackers@freebsd.org Subject: Re: zfs support in makefs Message-ID: <d907e65a-2a1a-7482-d533-f4c18841d8ca@freebsd.org> In-Reply-To: <20220518230427.GI15201@spindle.one-eyed-alien.net> References: <YoVC9VgV1nTptjzx@nuc> <20220518230427.GI15201@spindle.one-eyed-alien.net>
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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.
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
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