Harddrive setup is:
/dev/sda1 /boot
/dev/sda2 swap
/dev/sda3 LUKS encrypted

Then on the encrypted partition, I used btrfs, but my Slackware root is really a subvolume named system and not the root of btrfs. I do a similar setup of having the OS's root in it's own filesystem on FreeBSD+ZFS.

Anyways, my problem lies in mkinitrd. There's no way to enter extra boot options, as I require subvol=system to be added to
mount -o ro -t $ROOTFS $ROOTDEV /mnt
in the init script of /boot/initrd.gz. I don't reboot often and it's easy to manually remount /mnt with the correct options, however, is there another way of passing boot options to mkinitrd?

I see Patrick is the author of mkinitrd, so maybe this kind of option could, or maybe should, be added? I'm sure most people wouldn't make a subvolume for the OS's root, but I've been use to it with ZFS and prefer it for some reason.

Hey - your post get me interested in btrfs file systems, (of which I have no experience), so I created a new Slackware VM in VirtualBox following Alien Bob's instructions for installing LUKS and LVM,( something I have done before), and utilizing a btrfs root file system, (something I have not done before), and everything worked OK.

Now admittedly I am not using subvolumes here so obviously your setup is more sophisticated than my test rig however would it not be possible to just edit /boot/initrd-tree/init and add your subvol=system bits manually to the "mount -o ro -t $ROOTFS $ROOTDEV /mnt" parts of the script and then create the initrd without adding the "-c" to clear initrd-tree? Mkinitrd is an amazing script and i'm sure it can easily create the new initrd from existing contents ot the /boot/initrd-tree. As said, this should create the initrd from the existing contents of /boot/initrd-tree including your edited mount parts. I hope so but I've not tried it - in any case thanks for your interesting post - I love new areas of Linux to experiment with, ( yes, I'm a total geek), and the combination of LUKS/LVM and btrfs got my interest!

I think I'll be looking into brtfs a lot as I have a fascination with different filesystems and their benefits. The Hammer filesystem, part of DragonFly BSD is personal a favourite.

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I could be wrong, but isn't LVM2 unnecessary with btrfs? I thought it had most of LVM2's features built-in.

Very possibly, as I said my experience of LUKS is limited and I have only ever combined it with LVM following Eric's instructions in README_CRYPT and as he says :
so it's possibly just me jumping in with the LVM additional bits. The OP made no mention of LVM's.

Perhaps the addition of a $ROOTOPTS variable to the initrd script would do it. Shouldn't be too hard.


I've not played with btrfs yet, but can you make use of
as a workaround?

Yes sir. I had the same idea, but forgot to drop the -c option, thank you.

Correct, with btrfs, no need for LVM. So my setup is LUKS + btrfs instead of LUKS + LVM.

Was wondering if Pat would be interested about adding something like $ROOTOPTS. Although, how many initrd's need extra mount options? The solution of editing the init script and not cleaning the tree seems to be a better approach, at least for now anyways.

Yep, I've done that before too.

Tip: create yourself a initrd_build.sh and put all the commands necessary to build your custom initrd in there. If you do it manually then sooner or later when it's time for a new kernel, you'll end up forgetting to do it.

And, I've done that before too.


Was the btrfs subvolume set-default suggestion no good for you?

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To be honest, once I saw the -c suggestion, I went "I'm an idiot." and never tried the set-default suggestion. Not sure I want to try set-default, as btrfs is essentially a partition manager also, so I can install several btrfs supported OSes all within one MBR/GPT partition. Thus one of the main reasons I do not use the btrfs root as the OS root, instead create a subvolume for the OS root.

Example:
OS #1: / - subvol=system; /usr - subvol=usr; /var - subvol=var; /home - subvol=home
OS #2: / - subvol=system2; /usr - subvol=usr2; /var - subvol=var2; /home - subvol=home

And so on, until I run out of storage space. And easy to delete an OS I no longer want to boot. All without ever needing to redo MBR/GPT partitions.

So in my case, I think it would be easier to make a second initrd.gz which has mount -o subvol=system2, and tell lilo in another entry to use that second initrd.gz. Your suggestion, I would have to issue the set-default command at each reboot that I wanted to switch OSes? I could be wrong though.

Already had a script to run mkinitrd, problem was it had the -c option in it. Operator error. Thank for the tips though.

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