How to share back modified code

[acbauer]

Hi, I'm working on a project that's using a modified libMesh. I'm not sure of the exact history. Our code was created in 2012 and is clear that it's using some libMesh code that's been modified. It's not clear if parts of libMesh have been taken from the main repo since then. Based on my understanding of libMesh's LGPL license, we need to share those changes back to the community. I can share a tarball of our current version in order to be compliant with the license but don't know where to put that. Any suggestions?

Thanks,
Andy

[jwpeterson]

I'm not a lawyer, but I think it's sufficient for you to say that "you will provide" a copy of the modifications upon request, and then if anyone requests them, you can send the tarball you mentioned. In addition, those modifications must be LGPL-licensed as well.

[roystgnr]

If you're only using changed versions of the library yourself, I think the only significant limitation is that you're supposed to keep track of which files are changed by you and when they were changed. If you're keeping changes in version control and changing files in-place then IMHO that's sufficient, and if you're not keeping changes in version control then I'd say you've got technical problems outweighing any legal problems. ;-) If you're creating new files that incorporate sections of LGPL files (at least sections which are big/expressive enough not to count as "fair use") then you should have some references (ideally comments in the new files, but again I'd say keeping the metadata in version control is fine) pointing people to the libMesh files where those excerpts came from.

I recall being told that, even to the GNU people, internal redistribution within a single organization counts as "yourself", so even if you're working in a group you may be done at this point!? But I wouldn't rely on that interpretation for myself. IP law is hard and it's best to say on the safe side of any gray areas.

If you're redistributing your changed version to others, even though your legal obligation is to all the affected libMesh copyright holders, the expression of that obligation is only to the people who are getting copies of the changed version. (A) They have to be able to redistribute the changed version under the LGPL too (which means your own library-level changes need to be LGPL or LGPL-compatibly licensed), and (B) you need to either: (1) provide them with source code (including the change history, if you're using that rather than change logs in the files themselves!) along with any binaries or (2) upload the changed source code to the same place where you got it.

(B)(1) is sufficient! Provide all your users the ability to make copies of your source code, licensed under the LGPL as a whole, and you're done. No need to send a tarball anywhere else, not even to us; you just can't restrict any of them from further redistributing a tarball if they so choose. You don't even need to make binary users download a copy of the source code, you just need to give them the option to download it from the same place they get binaries.

I am, however, a bigger fan of (B)(2)! IMHO a plain tarball is too unwieldy for me to look at personally, but I certainly wouldn't object to one, and if you could push a version control repo (even if you forked so long ago that you need to reposurgeon it from svn to git first) to Github that would be awesome!