Re: Intended destination for symlinks after subvolume snapshot

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On 15 September 2015 at 13:38, Kai Krakow <hurikhan77@xxxxxxxxx> wrote:
> Marc O'Morain <marc@xxxxxxxxxxxx> 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).

Thanks Kai.
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