Unable to build cdrom: failed to setup loop device

[Robin Roevens <robin.roevens@disroot.org>]

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Hi all

While trying to build ipfire, which always has worked quite effortless,
it now fails while building cdrom:

---
    # Create the EFI Eltorito image
    dd if=/dev/zero of=/tmp/cdrom/boot/isolinux/efiboot.img bs=1k
count=2880
    2880+0 records in
    2880+0 records out
    2949120 bytes (2.9 MB, 2.8 MiB) copied, 0.00453183 s, 651 MB/s
    mkdosfs -F 12 -n "IPFIRE_EFI" /tmp/cdrom/boot/isolinux/efiboot.img
    mkfs.fat 4.2 (2021-01-31)
    # Mount the EFI image
    mkdir -pv /tmp/efiboot.img
    mkdir: created directory '/tmp/efiboot.img'
    mount -o loop /tmp/cdrom/boot/isolinux/efiboot.img /tmp/efiboot.img
    mount: /tmp/efiboot.img: failed to setup loop device for
/tmp/cdrom/boot/isolinux/efiboot.img.
    make: *** [cdrom:184: /usr/src/log/cdrom] Error 32
    make: Leaving directory '/usr/src/lfs'

ERROR: Building cdrom                                                 
[ FAIL ]
    Check /home/robin/src/ipfire-sandbox/ipfire-
2.x/log_x86_64/_build.ipfire.log for errors if applicable             
[ FAIL ]
---

The logfile has no extra or new information.

When I manually try those steps, as root (as make.sh is also ran as
root (using sudo)), they work correctly, and I'm able to successfully
mount the image.

---
$ sudo dd if=/dev/zero of=./efiboot.img bs=1k count=2880 
2880+0 records gelezen
2880+0 records geschreven
2949120 bytes (2,9 MB, 2,8 MiB) gekopieerd, 0,0130511 s, 226 MB/s
$ sudo ./build/sbin/mkdosfs -F 12 -n "IPFIRE_EFI" ./efiboot.img
mkfs.fat 4.2 (2021-01-31)
$ sudo mkdir ./efi
$ sudo mount -o loop ./efiboot.img ./efi
$ df -h ./efi                                                         
Bestandssysteem Grootte Gebruikt Besch Geb% Aangekoppeld op
/dev/loop15        2,8M        0  2,8M   0% /home/robin/src/ipfire-
sandbox/ipfire-2.x/efi
---

So I'm unsure as of why the build fails setting up the loop device.
I did a ./make.sh clean, but that didn't solve it.

If I try to mount the loop device as unprivileged user, I get the exact
same error. But the build process is ran as root, so that should also
not be the problem?

Has anyone an idea what could be wrong here? or give me some guidelines
on how to debug this ? 
I've read there where changes to the inner workings of the build
system, could those be the cause ? I assume not as then I would have
seen others complain about it here?

Robin