Re: [RFC PATCH 02/24] erofs: add superblock data structure in Rust

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2024/9/17 13:34, Greg KH wrote:
> On Tue, Sep 17, 2024 at 08:18:06AM +0800, Gao Xiang wrote:
>> Hi Greg,
>>
>> On 2024/9/17 01:55, Greg KH wrote:
>>> On Mon, Sep 16, 2024 at 09:56:12PM +0800, Yiyang Wu wrote:
>>>> diff --git a/fs/erofs/rust/erofs_sys.rs b/fs/erofs/rust/erofs_sys.rs
>>>> new file mode 100644
>>>> index 000000000000..0f1400175fc2
>>>> --- /dev/null
>>>> +++ b/fs/erofs/rust/erofs_sys.rs
>>>> @@ -0,0 +1,22 @@
>>>> +#![allow(dead_code)]
>>>> +// Copyright 2024 Yiyang Wu
>>>> +// SPDX-License-Identifier: MIT or GPL-2.0-or-later
>>>
>>> Sorry, but I have to ask, why a dual license here?  You are only linking
>>> to GPL-2.0-only code, so why the different license?  Especially if you
>>> used the GPL-2.0-only code to "translate" from.
>>>
>>> If you REALLY REALLY want to use a dual license, please get your
>>> lawyers to document why this is needed and put it in the changelog for
>>> the next time you submit this series when adding files with dual
>>> licenses so I don't have to ask again :)
>>
>> As a new Rust kernel developper, Yiyang is working on EROFS Rust
>> userspace implementation too.
>>
>> I think he just would like to share the common Rust logic between
>> kernel and userspace.
> 
> Is that actually possible here?  This is very kernel-specific code from
> what I can tell, and again, it's based on the existing GPL-v2 code, so
> you are kind of changing the license in the transformation to a
> different language, right?

It's possible, Yiyang implemented a total userspace Rust crates
to parse EROFS format with limited APIs:

https://github.com/ToolmanP/erofs-rs

Also take another C example, kernel XFS (fs/libxfs) and xfsprogs
(userspace) use the same codebase.  Although they both use GPL
license only.

> 
>> Since for the userspace side, Apache-2.0
>> or even MIT is more friendly for 3rd applications (especially
>> cloud-native applications). So the dual license is proposed here,
>> if you don't have strong opinion, I will ask Yiyang document this
>> in the next version.  Or we're fine to drop MIT too.
> 
> If you do not have explicit reasons to do this, AND legal approval with
> the understanding of how to do dual license kernel code properly, I
> would not do it at all as it's a lot of extra work.  Again, talk to your
> lawyers about this please.  And if you come up with the "we really want
> to do this," great, just document it properly as to what is going on
> here and why this decision is made.

Ok, then let's stay with GPL only.  Although as I mentioned,
cloud-native applications are happy with Apache-2.0 or MIT, which
means there could be diverged for kernel and userspace on the Rust
side too.

Thanks,
Gao Xiang

> 
> thanks,
> 
> greg k-h