Understanding merge window and next-tree

[Greg KH]

On Fri, Sep 10, 2021 at 04:06:39PM +0000, Lafan Mining wrote:
> I'm trying to understand how Linux Kernel development works and reading the relevant documentation at https://www.kernel.org/doc/html/latest/process/2.Process.html
> 
> So there is the so called next-tree accumulating all the patches from all the subsystems ready for merge and the mainline tree. The thing is the merge-window is opened for 2 weeks (as mentioned in the linked documentation) and as far as I understood all the changes will be merged into the mainline.
> 
> But looking through the next-tree I found some implementation in Rust https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/rust which is much older than 2 months.
> 
> How is that happened that after a few merge windows (4 if I counted correctly) it's still not merged?

Maintainers have to ask Linus to take their changes and be merged, Linus
does not directly merge from linux-next.  This allows for maintainers to
"skip" merge windows if needed, as well as have things in linux-next for
a long time before they go to Linus for various reasons (the -mm tree
has many such patches, and so does the rust tree as you have seen.)

So yes, the requirement is that changes have to be in linux-next before
it goes into Linus's tree, but it does not guarantee that anything is in
linux-next will end up in Linus's tree.

Does that help?

greg k-h