If you took the code from Linux, you need to add the original
Signed-off-by from the Linux commit. Aside from that:
There are multiple commits touching this function. So I followed what we did in similar situation. By that I mean, mentioning the code was taken from Linux and not gathered the signed-off-by.
If you really want, I can gather all the signed-off-by of the commit touching this function.
If there are a lot of then, you may want to consider adding a README.source file instead. There are a few examples in tree and they are also mentioned in CONTRIBUTING files
I am not sure to understand your suggestion here. I spotted only one CONTRIBUTING file and it only list the license.
I was suggesting to create a README.source in the xen arm tree seomwhere where you can list imports.
Regarding README.source, this is covering file and contain the same mention as in the commit message. As this is a single function. Isn't the commit message enough?
From a legal viewpoint it is enough.
The reason why we created the README.source file is because it is very easy to miss code imports when they are mentioned in commit messages.
Normally this isn't a problem: only if we ever have to relicense the code or if someone does code archeology
Lastly, we do have quite a bit of code in Xen coming from Linux (or other project). A lot of them are not listed in README.source/CONTRIBUTING. But only mention in the commit message (not necessarily with Signed-off-by tag).
That is true: which is why I have started fixing these, whenever I found them and moved such information to README.source.
* I would prefer if people added import related info README.source files (and also in the commit message)