[RESOLVED] calamares crash attempting to install into in use btrfs

[jlittle]

For several years, at least 5, when there's a new release I've often done an install into the same btrfs as other installs, having set up those other installs to use subvolumes other than @ and @home. I choose manual install and select the file system where I want it to go, and set it put "/" there. I don't set up /boot/efi anywhere; calamares warns about it but carries on. I set no swap partition.

Now with 25.04 calamares crashes shortly after starting the install with:

Create subvolume '/tmp/calamares-root-nqq5css3/@'
Create subvolume '/tmp/calamares-root-nqq5css3/@home'
ERROR: Could not create subvolume: File exists
Python Error:
 <class 'subprocess.CalledProcessError'>
 None
 File "/usr/lib/x86_64-linux-gnu/calamares/modules/mount/main.py", line 384, in run
    mount_partition(root_mount_point, partition, partitions, mount_options, mount_options_list, efi_location)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/usr/lib/x86_64-linux-gnu/calamares/modules/mount/main.py", line 292, in mount_partition
    subprocess.check_call(["btrfs", "subvolume", "create",
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                           root_mount_point + s["subvolume"]])
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

@ and @home do not exist before running calamares. (They do after the crash, mounted somewhere under /tmp.)

Is it still possible to install into @ and @home on an existing btrfs? (It would be good not to go back to shuffling partitions around.)

I've had calamares crashes with previous releases, usually involving a swap file, and I've been able to get past them by hacking the Python to just not run the code that crashes. But this crash seems not so simple.

[jlittle]

Today, I installed 25.04 to an ancient HDD, so that I could then move it to my main btrfs (a cheapo NVMe). The move was easy, two copies and adjusting /etc/fstab and grub,but I noticed a subvolume called @swap.

So, now kubuntu installs to @, @home and @swap. To install to an existing btrfs alongside other installs in that same btrfs, one must make sure those 3 names are free, or calamares crashes.