Fail to find partition on loop device inside container

[simoberny]

Good morning,
I'm having a problem with creating and using a loop device interface, in particular using internal partition.
I'm using Yocto to create an image. I've already done this on a separate machine, and I moved to proxmox machine recently reproducing the same steps.

I'm using a Ubuntu 22.04 container. VE 8.1.4. Evething updated.

My steps are as follows:
I created my image using dd

dd if=/dev/zero of=image.img bs=1M count=15000

Since by deafult Proxmox does not create loop device interface I manually created the /dev/loop0

sudo mknod -m 0660 /dev/loop0 b 7 8

Than I attach the .img to the device, and I check if image is correctly associated.
Everything seems ok as for now

sudo losetup -Pf image.img
losetup -a | grep image.img

Than I launched the script the vendor provide to create the extended .img ready to flash on SD.
It correctly create a partition, that is showed on fdisk -l command (showed below).

sfdisk --force -uS ${node} &> /dev/null << EOF
${PART1_START},${PART1_SIZE},83
EOF

fdisk -l

Creating new partitions                                                                                                                                             
16384                                                                                                                                                               
15155200                                                                                                                                                            
Disk /dev/loop0: 14.65 GiB, 15728640000 bytes, 30720000 sectors                                                                                                     
Units: sectors of 1 * 512 = 512 bytes                                                                                                                               
Sector size (logical/physical): 512 bytes / 512 bytes                                                                                                               
I/O size (minimum/optimal): 512 bytes / 512 bytes                                                                                                                   
Disklabel type: dos                                                                                                                                                 
Disk identifier: 0x6cc5f676                                                                                                                                         
                                                                                                                                                                    
Device       Boot Start      End  Sectors  Size Id Type                                                                                                             
/dev/loop0p1      16384 15171583 15155200  7.2G 83 Linux

The script fails on the formatting step:

 mkfs.ext4 ${node}${part}1 -L rootfs

Formatting partitions                                                                                                                                               
mke2fs 1.46.5 (30-Dec-2021)                                                                                                                                         
The file /dev/loop0p1 does not exist and no size was specified.

The partition appears to exist, but in reality write commands don't seem to find it.

I've read a few threads here on the site where it seems like the kernel isn't being updated with the new partition table. But that's not the case, and I've already tried every piece of advice I could find and none of it seems to work.

Thanks for any help,
Bests

UPDATE 1

Further investigation show kernel module seems missing.
On my prev ubuntu machine modprobe show the module as built-in.
On container the modprobe command:

sudo modprobe loop
modprobe: FATAL: Module loop not found in directory /lib/modules/6.5.11-8-pve

On the host instead:

root@yocto:/etc/pve/lxc# modinfo loop
name:           loop
filename:       (builtin)
alias:          devname:loop-control
alias:          char-major-10-237
alias:          block-major-7-*
license:        GPL
file:           drivers/block/loop
parm:           max_loop:Maximum number of loop devices
parm:           max_part:Maximum number of partitions per loop device (int)
parm:           hw_queue_depth:Queue depth for each hardware queue. Default: 128

UPDATE 2

I now noticed that when I create a partition like /dev/loop0p1, this shows up in the host machine, as it should, but is not reflected in the container. This is the piece I am missing. I could not map the partition in the container conf, since it does not exist when container is started.