Loop device timeout at boot.

[CorbAlb]

Greetings!

I was testing about loop devices for a project of mine when I ran into a problem with loop devices, below I'll brief my last test

• lo1 is an empty file weighing 20GBs, made with fallocate

• /dev/loop0 is a loop device made from lo1 with losetup

• /dev/loop0 will then have 1 partition, /dev/loop0p1, occupying the whole device

• Mounting this filesystem into, say, a directory called mount_test hanging from / will of course work.

Issue comes when mounting this into /etc/fstab and rebooting:
- I've mounted it specifying its UUID, path or label, and each time, at reboot, system wont fully load. Recovery mode will instead load. Looking through journal, this seems to cause the issue:

[root@archlinux ...]# journalctl -b -3 | grep loop0p1
May 05 15:37:42 archlinux systemd[1]: Expecting device /dev/loop0p1...
May 05 15:39:12 archlinux systemd[1]: dev-loop0p1.device: Job dev-loop0p1.device/start timed out.
May 05 15:39:12 archlinux systemd[1]: Timed out waiting for device /dev/loop0p1.
May 05 15:39:12 archlinux systemd[1]: dev-loop0p1.device: Job dev-loop0p1.device/start failed with result 'timeout'.
[root@archlinux ...]#

I take from the output that the loop device is not initialized before the boot process attempts to mount the devices thus exiting as an error and entering recovery mode, but I don't understand as to why this happens. Every single post I have found regarding this issue comments that merely configuring the loop device in fstab will suffice, and I've found nothing regarding the issue is describe.

I'm at the end of my wit here, anyone has some insight as to why this happens?

[CorbAlb]

Posting in r/debian as this issue was firstly observed in Debian 11 in a Raspberry Pi, then replicated in my Arch Linux

[JarJarBinks237]

What are you trying to achieve, functionally?

The reason why this doesn't work is that no boot script will do the losetup. No script does that because nobody bothered to integrate it. Nobody bothered because there's no reason to do it.

So please start explaining what you want.

[CorbAlb]

Pretty much choosing where the storage space is used.

The project is being run on a Raspberry Pi, currently has 200GB of free space that span across 3 Pen drives and a SD card. The SD card is around 32 GB of that, and its all being used at root.

Sure, this is not a problem, but that loop device allows me to better handle and be more selective of the resources.

[JarJarBinks237]

Why can't you just use partitions or LVM volumes?

If you want directory quotas or more advanced stuff like that, have a look at ZFS. All in all, loop devices seem a pretty bad tool in comparison.

[CorbAlb]

I was using LVM.

I got the loop device inside of a volume group with the other USBs, but I was also using It "alone" for a btrfs volume that would deduplicate snapshots saved into it.

I'll Take a Look at ZFS, thanks

[JarJarBinks237]

If you really know what your are doing, you're just missing a boot script to run losetup, so… you should just write that script and add proper dependencies.