[Libguestfs] ZFS Support

[Richard W.M. Jones]

On Thu, Oct 12, 2017 at 09:46:13AM +0200, Miha Pleško wrote:
> 
> Dear libguestfs developers, 
>
> as explained yesterday by Ubuntu guys on my bug report
> https://bugs.launchpad.net/ubuntu/+source/libguestfs/+bug/1722800
>
> the libguestfs currently supports ZFS filesystem only partially
> i.e. for virt-rescue.
>
> Q: Would it be possible to bring ZFS support also to other
> libguestfs utils, like guestfish and virt-format?
>
> I would need to have two usecases supported: 

Thanks for posting here.  As you say, ZFS support in libguestfs is
currently very limited.  Enabling it basically adds the userspace
package so it's available in virt-rescue, if you manually use the
‘zfs’/‘zpool’/etc commands.

> a) create a new volume with ZFS filesystem / format existing volume
> into ZFS filesystem

We could fairly easily make simple things work like creating a
filesystem.  This is a good beginners patch as it just involves making
simple adjustments to this function:

  https://github.com/libguestfs/libguestfs/blob/master/daemon/mkfs.c#L35

> b) manage files from ZFS volume (read, write) 

I believe that mounting a ZFS volume should just work currently.  If
not, you might need to make only simple adjustments to the mount API:

  https://github.com/libguestfs/libguestfs/blob/master/daemon/mount.ml#L24

This should allow you to read and write files.

Providing full ZFS volume management is a quite a bit harder.  It
would involve pulling in some of the zfs APIs and turning them into
libguestfs APIs.  There is lots of documentation about how to add new
APIs here:

  http://libguestfs.org/guestfs-hacking.1.html#extending-libguestfs

I would start by looking at how other APIs have been implemented.
Particularly relevant would be the LVM and btrfs APIs, eg:

  https://github.com/libguestfs/libguestfs/blob/master/daemon/btrfs.c

Rich.

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