[PATCH v3 0/5] Implement reflink support

[Alexandre Julliard]

"Alex Xu (Hello71)" <alex_y_xu at yahoo.ca> writes:

> Excerpts from Fabian Maurer's message of January 27, 2022 5:24 pm:
>> Hello,
>> 
>> first, thanks for working on this, would be a welcome improvement!
>> Do I understand that right that it wouldn't work for ext4 and there's not
>> really anything we could do to support it?
>> 
>> Regards,
>> Fabian Maurer
>
> ext4 does not support reflink, so copy_file_range cannot reduce disk 
> space usage. However, it will still allow the kernel to do the file copy 
> itself, avoiding copying the data to userspace.
>
> Full reflink functionality with arbitrary offsets and overwrite is 
> non-trivial to implement in the filesystem. However, we really only need 
> the limited functionality of a whole-file reflink. This could be 
> simulated using a hard or symbolic link which gets broken by Wine when 
> any write occurs. However, as with reparse points, this requires 
> modifying every file access that Wine makes, which would be a 
> significant undertaking.

I'm not convinced that it would be that hard, and if it can work it
would clearly be a better approach. Prefix size is a real problem, but I
don't think reflinks are the answer.

-- 
Alexandre Julliard
julliard at winehq.org