How to mount a zfs poolfile with dataset as a loopback?

I have a installed Ubuntu 22.04.1 (from 22.04.1-desktop-amd64.iso), running at VirtualBox 7, with installed zfs-tools.

I have an image file from a zfs pool called zfsfile01. I can look in this file with:

fdisk -l zfsfile01

and I get the value with 2 datasets: dataset01 and dataset02 - the file seems to be ok.

Now I have to mount the file zfsfile01 itself or the second dataset02 as a loopback device. After reading some useful texts, I recognized that I have to first import the poolfile with zpool and then mount a filesystem (a dataset?) from the poolfile with zfs mount. Importing the pool with

zpool import <pathto>/zfsfile01

failed with:

cannot import <pathto>/zfsfile01: no such pool available

I guess because of the file and no right zfs pool.

Basically, I can go on with the mount command in Linux and can mount a dumped file with sudo mount -o loop,offset=xxx image.dd /tmp/destination and such stuff. But I don't know which options I have to use to mount a zfs pool file with dataset as a loop back device.

Here is the output of sudo fdisk -l zfsfile01: (response to comment)

Festplatte ewf1: 1,82 TiB, 2000398934016 Bytes, 3907029168 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
Festplattenbezeichnungstyp: gpt
Festplattenbezeichner: 44E0E83D-A9CA-11EC-xxxx-xxxxx
Gerät       Anfang       Ende       Sektoren   Größe Typ
dataset1    128          4194431    4194304    2G FreeBSD Swap
dataset2    4194432      3907029127 3902834696 1,8T FreeBSD ZFS

Here is the output of losetup: (response to Artur's answer)

$ losetup -f
/dev/loop8
$ sudo losetup /dev/loop8 /media/sf_E_DRIVE/zfsfile01
losetup: /media/sf_E_DRIVE/zfsfile01: Loop-Gerät konnte nicht eingerichtet werden: Vorgang nicht zulässig

I can loop a dd image with:

sudo losetup /dev/loop8 /media/image.dd 

and then I can un-loop the device with:

sudo losetup -d /dev/loop8

But I get an error with zfsfile01:

Loop-Gerät konnte nicht eingerichtet werden: Vorgang nicht zulässig

which means:

cannot setup loop-device: progress is not valid

I found a guide here, that hopefully is applicable to your case.

This is how I would translate it to your situation:

1. Mount image as loop device:

   # losetup /dev/loop100 /<pathto>/zfsfile01
   

2. Create partitions (only if the image contains partitions):

   # kpartx -av /dev/loop100
   add map loop100p1 (252:0): <something>
   add map loop100p9 (252:1): <something>
   

3. Create mount point:

   # mkdir /mnt/<poolname>
   

4. Try to import the ZFS pool with this pool name:

   # zpool import -R /mnt/<poolname> -d /dev/mapper
      pool: <poolname>
        id: <specific ID>
     state: ONLINE
    status: Some supported features are not enabled on the pool.
    action: The pool can be imported using its name or numeric identifier, though
            some features will not be available without an explicit 'zpool upgrade'.
    config:
   
           <poolname>       ONLINE
             loop100        ONLINE
   

5. With the ID from previous result, you can import the pool with new options and name (if necessary - maybe you can skip this step and just use <poolname> in the following):

   # zpool import -o readonly=on -f -d /dev/mapper <specific ID> <new_poolname> -R /mnt/<poolname>
   

6. Done:

   # zpool status
     pool: <new_poolname>
    state: ONLINE
   status: Some supported features are not enabled on the pool. The pool can
           still be used, but some features are unavailable.
   action: Enable all features using 'zpool upgrade'. Once this is done,
           the pool may no longer be accessible by software that does not support
           the features. See zpool-features(5) for details.
     scan: none requested
   config:
   
           NAME             STATE     READ WRITE CKSUM
           <new_poolname>   ONLINE       0     0     0
             loop100        ONLINE       0     0     0
   
   errors: No known data errors
   
   # zfs list <new_poolname> -r
   NAME                       USED  AVAIL  REFER  MOUNTPOINT
   <new_poolname>             xxxM  xxxxG  xxK  /mnt/<poolname>
   <new_poolname>/dataset01   xxxM  xxxxG  xxK  /mnt/<poolname>/dataset01
   <new_poolname>/dataset02   xxxM  xxxxG  xxK  /mnt/<poolname>/dataset02