Re: Intended destination for symlinks after subvolume snapshot

[Kai Krakow <hurikhan77@gmail.com>]

Marc O'Morain <marc@circleci.com> schrieb:

> Hi all,
> 
> What is the intended destination of a symlink inside a subvolume after
> a snapshot?
> 
> When I take a snapshot of a subvolume that contains a symlink, the
> symlink points outside the snapshot and into the original subvolume.
> 
> Is this the intended behaviour? Or should the symlinks be patched up
> to point inside the snapshot?
> 
> Here is an example that creates a new subvolume, a file and a symlink
> to the file. It then creates a snapshot and shows the destination of
> the symlink.
> 
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# mount | grep btrfs
> /dev/loop0 on /mnt/btrfs type btrfs (rw)
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# btrfs subvolume create
> subvolume0 Create subvolume './subvolume0'
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# touch subvolume0/readme.txt
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# ln -s
> /mnt/btrfs/subvolume0/readme.txt /mnt/btrfs/subvolume0/readme.lnk
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# btrfs subvolume snapshot -r
> subvolume0 snapshot0
> Create a readonly snapshot of 'subvolume0' in './snapshot0'
> root@vagrant-ubuntu-trusty-64:/mnt/btrfs# tree
> .
> ├── snapshot0
> │   ├── readme.lnk -> /mnt/btrfs/subvolume0/readme.txt
> │   └── readme.txt
> └── subvolume0
>     ├── readme.lnk -> /mnt/btrfs/subvolume0/readme.txt
>     └── readme.txt
> 
> 2 directories, 4 files
> 
> (I was expecting snapshot0/reame.lnk to point to
> /mnt/btrfs/snapshot0/readme.txt)

If you use absolute symlinks this is intended behaviour and probably has its 
use cases (similar to when you move subdirectories or create a copy, 
symlinks aren't rewritten either).

You should use relative symlinks for your use case (this means, do not start 
with "/", instead walk up with ".." if needed).

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