Problems mounting btrfs subvolumes within a dm_crypt volume

[jbiggs12]

Hello all,

I've installed gentoo, and unfortunately I'm having a bit of a problem with dm_crypt. Within the dm_crypt volume is a btrfs filesystem with 3 subvolumes: one for /, one for /var, and one for /home. In my custom initramfs I have the line:

[wildbug]

I came here looking to solve exactly the same problem. I can't solve it, but I think I can explain it.

In your initramfs, when you mount your dm-crypt volume, it's mounted under /dev/mapper/crypt; this is your btrfs root (subvolid=0). You mount your system root subvolume (subvol=root) at /mnt/root, and presumably issue something like "switch_root /mnt/root /sbin/init" at the end of your initramfs init script. switch_root puts your /mnt/root over the current /, masking it and also masking the /dev/mapper/crypt mountpoint, which is why you can't see it once your system's up.

Is there any way to access the btrfs root volume after switch_root masks /dev/mapper?

I suppose you could mount other filesystems on mountpoints under your root in initramfs before switch_root, but that seems wrong, and I'd like to optionally mount the btrfs root instead of always having it available.

[wildbug]

Using devtmpfs instead of busybox's mdev solves this for me. You'll need to compile it into your kernel (CONFIG_DEVTMPFS under Device Drivers > Generic Driver Options) and mount it with "mount -t devtmpfs none /dev" in your initramf's /init script.

[jbiggs12]

Well hate to burst your bubbles but I got impatient after nobody replied, gave up, and now have a different setup. Instead of having a separate subvolume for the root directory, I made /var, /usr, and /home all subvolumes within the main one and simply mounted subvolid 0, addressing all of the subvolumes as folders.