Main Linux kernel vs Ubuntu kernel

[greg@kroah.com (Greg KH)]

On Sat, Jun 09, 2018 at 05:17:45PM +0530, Subhashini Rao Beerisetty wrote:
> My question related to backward compatibility is: If an API?s signature
> changed from kernel version x.y.z onwards, does the mainline tree code uses
> the below mentioned logic?
> 
> 
> #if LINUX_VERSION_CODE >= KERNEL_VERSION(x,y,z)
> 
> #else
> 
> #endif

No, mainline kernel code does not have #ifdefs at all, it is not needed.

Remember, all drivers are included in the kernel release at once, so
there is no need for such checks as they all work for the kernel they
are contained in.

> Regarding long term release kernels, what here ?long term? means?

Did you read this:
	https://www.kernel.org/category/releases.html

It should explain all of this.

> For e.g.  v4.4 is part of long term release kernel released in
> 2016-01-10 and it?s projected EOL is Feb, 2022, here what?s the
> meaning of EOL?

End Of Life.

> How to backport the bug fixes for older kernel tree (for e.g. v4.4) and
> what is the selection criteria for choosing which bug fixes should go for
> backporting?

Did you read this:
	https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

Also, please read the kernel development process documentation, it
should have answered these questions for you and will cover lots of this
type of thing.

thanks,

greg k-h