Accessing Parent Subvolume

Accessing Parent Subvolume

[Imran Geriskovan]

It's a common case for installing new operating system on
subvolumes on an existing btrfs. So I'll base my example on it:

** SETUP **
We have the following subvolumes:

- OS1 (say Debian) on default subvolume /
- OS2 (say Arch) on subvolume /@arch

Now, boot into Arch and mount its parent
subvolume on /mnt/debian.


** QUESTIONS **
1- Is it safe to access /mnt/debian ?
2- Is it safe to access /mnt/debian/@arch ?
(Yeah, I'm pushing my chances recursively)


** POSSIBLE ANSWERS **
X- Sure.. Accessing parent subvolumes recursively is a
non issue. Even /arch/debian/arch/debian... is no problem.
(Then, add this to features/decumentation to show how
generic btrfs subvolume mount machinery is)

Y- Btrfs is designed to do that. However, expect some
corner cases/bugs. (It's okay)

Z- Don't even do that. Btrfs is never designed for it and
will never be. (Then, prevent user doing it)


I wonder where btrfs is on XYZ scale.

Thanks for your comments,
Imran

Re: Accessing Parent Subvolume

[Goffredo Baroncelli]

On 2015-05-03 08:19, Imran Geriskovan wrote:
> ** QUESTIONS **
> 1- Is it safe to access /mnt/debian ?
> 2- Is it safe to access /mnt/debian/@arch ?
> (Yeah, I'm pushing my chances recursively)
> 
> 
> ** POSSIBLE ANSWERS **
> X- Sure.. Accessing parent subvolumes recursively is a
> non issue. Even /arch/debian/arch/debian... is no problem.
> (Then, add this to features/decumentation to show how
> generic btrfs subvolume mount machinery is)

It is safe. However I suggest to use the root subvolume only to host other subvolumes.

In your case the layout should be:

/@debian
/@arch

The biggest advantage is that all subvolume are equal, so it could be
manage in the same way when you do a snapshot/rollback...

BR
G.Baroncelli

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