Re: [patch V5 01/11] Documentation: Add license-rules.rst to describe how to properly identify file licenses

From: Yang Li
Date: Fri Jun 15 2018 - 12:55:29 EST

On Tue, Jun 12, 2018 at 2:27 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> Yang,
> On Tue, 12 Jun 2018, Yang Li wrote:
>> On Thu, Dec 28, 2017 at 4:17 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> > On Thu, 28 Dec 2017, Thomas Gleixner wrote:
>> >
>> > Sorry for the spam. I somehow missed to refresh the patch before generating
>> > the mbox. Find below the correct version of that one which has ALL braces
>> > removed which we don't need.
>> I'm not sure how we reached the conclusion that we should remove ALL
>> braces? I cannot find related discussion in the archive except for
>> the "WITH" case.

Thanks Thomas, But this email is mostly discussing the "WITH" case as
I said, and it does mentioned that braces is (weakly) needed for other

>> This is conflicting with the current SPDX spec at
>> quoted below and
>> also the explenation in your own file.
>> Quote from SPDX spec 2.1: More expressive composite license
>> expressions can be constructed using "OR", "AND", and "WITH" operators
>> similar to constructing mathematical expressions using arithmetic
>> operators. For the Tag:value format, any license expression that
>> consists of more than one license identifier and/or LicenseRef, should
>> be encapsulated by parentheses: "( )".
> This is not relevant here:
> For the Tag:value format, .....
> The kernel does not generate SPDX files in Tag:value format. The kernel
> uses SPDX license identifiers to reflect the actual license of a file.

I'm not sure if I understood the Tag:value term correctly. But it
looks like to me that the "SPDX-License-Identifier: <SPDX License
Expression>" is a tag:value in the SPDX spec.

"The tag should appear on its own line in the source file, generally
as part of a comment.

SPDX-License-Identifier: <SPDX License Expression>"

>> > + A <SPDX License Expression> is either an SPDX short form license
>> > + identifier found on the SPDX License List, or the combination of two
>> > + SPDX short form license identifiers separated by "WITH" when a license
>> > + exception applies. When multiple licenses apply, an expression consists
>> > + of keywords "AND", "OR" separating sub-expressions and surrounded by
>> > + "(", ")" .
>> Conflicting with the example
> No, The keyword is 'separating sub-expressions'. It does not say license
> identifiers.

But the first sentense declared that an expression can just be a short
form license identifier.

And the examples provided in the spec also proves it:


SPDX-License-Identifier: (GPL-2.0 OR MIT)
SPDX-License-Identifier: (LGPL-2.1 AND BSD-2-CLAUSE)
SPDX-License-Identifier: (GPL-2.0+ WITH Bison-exception-2.2)"

> So these examples are completely compliant with the documentation:
>> > + // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
>> > + // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note
>> > + // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
> Two license (exception) identifiers plus a operator. That's perfectly well
> defined.
>> > + // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) OR MIT
> This is actually a case where you need parentheses and they separate the
> sub-expression 'ID with EXC'.
> Adding extra parentheses around any simple 'ID operator [ID|EXC]'
> expression is really overkill and does not make stuff more
> readable. Likewise in programming languages. Why would anyone write:
> C et al.: a = (b || c);
> Pyhton: a = (b and c)

I think I agree with you that not having parentheses in these cases
probably make more sense. But I think we are having a conflict with
the spec now, probably we should update the SPDX spec to be aligned?
Actually a lot of the current SPDX tags in kernel tree are following
the spec to use the parentheses. We should do something to avoid the
confusion in the future IMO.