fungi: Is there any way to avoid it. I get this umount error every time. I looked at the diskimage build log, the cirrors image download was completed, most elements completed their jobs, and then an error occurred when unmount, resulting in an unsuccessful final build. and also show this lastly. but this should not be the reason for the build error.
```
2022-04-12 04:58:01.406 | INFO diskimage_builder.block_device.utils [-] Calling [sudo fstrim --verbose /var/cache/nodepool/dib_tmp/dib_build.OuW0QXUa/mnt/]
2022-04-12 04:58:01.444 | DEBUG diskimage_builder.block_device.utils [-] exec_sudo: fstrim: /var/cache/nodepool/dib_tmp/dib_build.OuW0QXUa/mnt/: the discard operation is not supported exec_sudo /usr/lib/python3.6/site-packages/diskimage_builder/block_device/utils.py:135
2022-04-12 04:58:01.448 | Traceback (most recent call last):
2022-04-12 04:58:01.448 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/lib/dib-block-device.py", line 7, in <module>
2022-04-12 04:58:01.448 |     sys.exit(main())
2022-04-12 04:58:01.448 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/cmd.py", line 120, in main
2022-04-12 04:58:01.448 |     return bdc.main()
2022-04-12 04:58:01.448 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/cmd.py", line 115, in main
2022-04-12 04:58:01.448 |     self.args.func()
2022-04-12 04:58:01.448 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/cmd.py", line 39, in cmd_umount
2022-04-12 04:58:01.449 |     self.bd.cmd_umount()
2022-04-12 04:58:01.449 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/blockdevice.py", line 442, in cmd_umount
2022-04-12 04:58:01.449 |     node.umount()
2022-04-12 04:58:01.449 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/level3/mount.py", line 111, in umount
2022-04-12 04:58:01.449 |     self.state['mount'][self.mount_point]['path']])
2022-04-12 04:58:01.449 |   File "/usr/lib/python3.6/site-packages/diskimage_builder/block_device/utils.py", line 143, in exec_sudo
2022-04-12 04:58:01.449 |     raise e
2022-04-12 04:58:01.449 | diskimage_builder.block_device.exception.BlockDeviceSetupException: exec_sudo failed
Exit code: 1
```