module: Cure the MODULE_LICENSE "GPL" vs. "GPL v2" bogosity
The original MODULE_LICENSE string for kernel modules licensed under the GPL v2 (only / or later) was simply "GPL", which was - and still is - completely sufficient for the purpose of module loading and checking whether the module is free software or proprietary. In January 2003 this was changed with commit 3344ea3a ("[PATCH] MODULE_LICENSE and EXPORT_SYMBOL_GPL support"). This commit can be found in the history git repository which holds the 1:1 import of Linus' bitkeeper repository: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=3344ea3ad4b7c302c846a680dbaeedf96ed45c02 The main intention of the patch was to refuse linking proprietary modules against symbols exported with EXPORT_SYMBOL_GPL() at module load time. As a completely undocumented side effect it also introduced the distinction between "GPL" and "GPL v2" MODULE_LICENSE() strings: * "GPL" [GNU Public License v2 or later] * "GPL v2" [GNU Public License v2] * "GPL and additional rights" [GNU Public License v2 rights and more] * "Dual BSD/GPL" [GNU Public License v2 * or BSD license choice] * "Dual MPL/GPL" [GNU Public License v2 * or Mozilla license choice] This distinction was and still is wrong in several aspects: 1) It broke all modules which were using the "GPL" string in the MODULE_LICENSE() already and were licensed under GPL v2 only. A quick license scan over the tree at that time shows that at least 480 out of 1484 modules have been affected by this change back then. The number is probably way higher as this was just a quick check for clearly identifiable license information. There was exactly ONE instance of a "GPL v2" module license string in the kernel back then - drivers/net/tulip/xircom_tulip_cb.c which otherwise had no license information at all. There is no indication that the change above is any way related to this driver. The change happend with the 2.4.11 release which was on Oct. 9 2001 - so quite some time before the above commit. Unfortunately there is no trace on the intertubes to any discussion of this. 2) The dual licensed strings became ill defined as well because following the "GPL" vs. "GPL v2" distinction all dual licensed (or additional rights) MODULE_LICENSE strings would either require those dual licensed modules to be licensed under GPL v2 or later or just be unspecified for the dual licensing case. Neither choice is coherent with the GPL distinction. Due to the lack of a proper changelog and no real discussion on the patch submission other than a few implementation details, it's completely unclear why this distinction was introduced at all. Other than the comment in the module header file exists no documentation for this at all. From a license compliance and license scanning POV this distinction is a total nightmare. As of 5.0-rc2 2873 out of 9200 instances of MODULE_LICENSE() strings are conflicting with the actual license in the source code (either SPDX or license boilerplate/reference). A comparison between the scan of the history tree and a scan of current Linus tree shows to the extent that the git rename detection over Linus tree grafted with the history tree is halfways complete that almost none of the files which got broken in 2003 have been cleaned up vs. the MODULE_LICENSE string. So subtracting those 480 known instances from the conflicting 2800 of today more than 25% of the module authors got it wrong and it's a high propability that a large portion of the rest just got it right by chance. There is no value for the module loader to convey the detailed license information as the only decision to be made is whether the module is free software or not. The "and additional rights", "BSD" and "MPL" strings are not conclusive license information either. So there is no point in trying to make the GPL part conclusive and exact. As shown above it's already non conclusive for dual licensing and incoherent with a large portion of the module source. As an unintended side effect this distinction causes a major headache for license compliance, license scanners and the ongoing effort to clean up the license mess of the kernel. Therefore remove the well meant, but ill defined, distinction between "GPL" and "GPL v2" and document that: - "GPL" and "GPL v2" both express that the module is licensed under GPLv2 (without a distinction of 'only' and 'or later') and is therefore kernel license compliant. - None of the MODULE_LICENSE strings can be used for expressing or determining the exact license - Their sole purpose is to decide whether the module is free software or not. Add a MODULE_LICENSE subsection to the license rule documentation as well. Signed-off-by:Thomas Gleixner <tglx@linutronix.de> Reviewed-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by:
Philippe Ombredanne <pombredanne@nexb.com> Acked-by:
Joe Perches <joe@perches.com> [jc: Did s/merily/merely/ ] Acked-by:
Jessica Yu <jeyu@kernel.org> Signed-off-by:
Jonathan Corbet <corbet@lwn.net>
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