Re: subvolumes as partitions and mount options

[Andrei Borzenkov <arvidjaar@gmail.com>]

On 28.03.2023 22:45, Matt Zagrabelny wrote:
> On Mon, Mar 27, 2023 at 8:42 PM Matthew Warren
> <matthewwarren101010@gmail.com> wrote:
>>
>> It looks like you already have it mostly set up correctly. You will
>> want to mount your filesystem somewhere without specifying a
>> subvolume.
> 
> Sure. Things are starting to make a little more sense.
> 
>   Then you can put all the subvolumes you want "hidden" in
>> there. This should be as simple as unomunting /subv_mnt, moving
>> subv_content to the btrfs root subvolume,
> 
> Right. My rootfs is mounted with a subvolume option, so I still can't
> get at the "root" subvolume:
> 
> # mount | grep btrfs
> /dev/nvme0n1p2 on / type btrfs
> (rw,relatime,ssd,space_cache=v2,subvolid=256,subvol=/@rootfs)
> 
> Thusly, I would need to unmount my root partition (presumably through

There is no need for this, multiple subvolumes can be mounted concurrently.

mount -o subvol=/ ...

> a live-cd or equivalent) and then mount:
> 
> mount /dev/nvme0n1p2 /mnt
> 

This depends on what default subvolume is and will not necessarily mount 
the top level of btrfs.

> and create my subvolume:
> 
> btrfs subvolume create /mnt/@foo
> 

"@" is just a convention, there is no magic in it, it is not *needed*.

> then boot back into my system with the regular root fs mount entry in
> /etc/fstab and then I can mount the subvolume as desired:
> 
> mount /dev/nvme0n1p2 /path/to/foo -o subvol=@foo
> 
> It looks like I can mount the root:
> 
> sudo -i
> mkdir /btrfs-fixer
> mount /dev/nvme0n1p2 /btrfs-fixer
> btrfs subvolume create /btrfs-fixer/@foo
> umount /dev/nvme0n1p2
> rm -rf /btrfs-fixer
> mount /dev/nvme0n1p2 /path/to/foo -o subvol=@foo
> 
> Not a bad work-around.
> 
> Thanks for all the help!
> 
> -m