Description of problem:
When I ask anaconda to mount multiple btrfs subvolumes during installation, only the subvolume connected as / is mounted correctly. All the other subvolumes are ignored, and the btrfs fsroot (the top level filesystem root) is mounted to the target places instead. For example, instead of mounting "subvol=home" into /home, "subvol=/" is mounted into /home instead.


Version-Release number of selected component (if applicable):
anaconda-40.21-2.fc40.x86_64
anaconda-webui-5.2-1.fc40.noarch
Fedora-Workstation-Live-x86_64-40-20240213.n.1.iso

How reproducible:
always

Steps to Reproduce:
1. in anaconda webUI (Workstation Live), go to custom (cockpit) storage
2. create biosboot (if needed) and /boot partitions
3. create a btrfs partition
4. in order to create a subvolume, the btrfs fsroot needs to be mounted, and you need to do it manually (for some reason). So click on three dots next to the "/ subvolume" (which is a bit confusing, it's not a subvolume, it's the fsroot), click Mount, and mount it (I picked "/" as the value, because I had no idea what to pick, this is all weird).
5. click on three dots next to the "/ subvolume" and create a "root" subvolume with "/" mountpoint
6. click on three dots next to the "/ subvolume" and create a "home" subvolume with "/home" mountpoint
7. see the attached screenshot and compare whether your layout looks the same
8. click "return to installation"
9. select the option to assign custom mount points
10. for "/" select the "root" device
11. for "/boot" select your boot partition, reformat it
12. add a new mount, set "/home" as the mount point, and pick the "home" device, do not format it
13. proceed with installation
14. during the installation or when it's done, look at `findmnt /mnt/sysroot` to see whether "subvol=root" is mounted there as it should be
15. also look at `findmnt /mnt/sysroot/home` whether "subvol=home" is mounted there as it should be. In my case, not it's not, instead "subvol=/" (the fsroot) is mounted there.
16. when the installation is complete, look at /mnt/sysroot/etc/fstab. /home should have "subvol=home" mount option. In my case, it doesn't have any except "defaults".



Actual results:
btrfs subvolume mounts are not mounted correctly, the fsroot is mounted there instead

Expected results:
btrfs subvolume mounts should match the selected values in the installer

Additional info:

During/after installation, I see this:

$ findmnt /mnt/sysroot
TARGET       SOURCE           FSTYPE OPTIONS
/mnt/sysroot /dev/vda3[/root] btrfs  rw,relatime,seclabel,compress=zstd:1,discard=async,space_cache=v2,subvolid=258,subvol=/root

$ findmnt /mnt/sysroot/home 
TARGET            SOURCE    FSTYPE OPTIONS
/mnt/sysroot/home /dev/vda3 btrfs  rw,relatime,seclabel,compress=zstd:1,discard=async,space_cache=v2,subvolid=5,subvol=/

Notice "subvol=/" instead of "subvol=home" ^^


$ cat /mnt/sysroot/etc/fstab 
<snip>
UUID=2247a71f-3504-4342-99ba-d5db7e7503ef /                       btrfs   subvol=root,compress=zstd:1 0 0
UUID=55ae4d71-a5a6-469d-bb2c-624235b36ccf /boot                   ext4    defaults        1 2
UUID=2247a71f-3504-4342-99ba-d5db7e7503ef /home                   btrfs   defaults        0 0

Notice missing "subvol=home" (and "compress") for /home.

When you have more subvolumes (e.g. "data" for /data), it behaves the same as in "home" case.


When you boot into the installed system, you can see that it uses the btrfs fsroot for /home. It creates user home directories in the top fstree, next to all the subvolumes present:

$ findmnt /home
TARGET SOURCE    FSTYPE OPTIONS
/home  /dev/vda3 btrfs  rw,relatime,seclabel,compress=zstd:1,discard=async,space_cache=v2,subvolid=5,subvol=/

$ ls /home
home  kparal  root

# list the contents of the actually intended location for /home
$ ls -A /home/home/  
$