Main Linux kernel vs Ubuntu kernel

[Subhashini Rao Beerisetty]

On Wed, Jun 13, 2018 at 12:02 AM, Seth Forshee <seth.forshee at canonical.com>
wrote:

> On Sat, Jun 09, 2018 at 12:07:12AM +0530, Subhashini Rao Beerisetty wrote:
> > [ Please keep me in CC as I'm not subscribed to the list]
> >
> >
> > Hi All,
> >
> >
> > Apologies for the dull questions, I’m noob, need to learn lot more stuff.
> >
> >
> > Ubuntu distro has LTS, non-LTS, GA, HWE kernels, what’s the difference
> > between these?
>
> GA: The kernel that originally ships with a given Ubuntu release.
>
> LTS kernel: The GA kernel for an LTS release (not to be confused with
> upstream LTS stable kernels - an Ubuntu LTS kernel may or may not also
> be an upstream LTS kernel).
>
> HWE kernel: A kernel backported from a non-LTS release to an LTS
> release.
>
> > Which one should be the best choice for development& validating the
> > hardware?
> >
> >
> > We’ve a bunch of hardware & test systems, we started this project by
> opting
> > ubuntu distro 16.04 LTS v4.4 kernel for development of device drivers,
> test
> > utilities.
>
> It's difficult to answer your question without more information about
> what you're hoping to accomplish. If you want to get new hardware
> support into Ubuntu, usually that would land in the upstream kernel
> first.
>
Thank you very much for the clarification.

We developed few out-of-tree linux kernel modules(we don’t distribute
drivers to external customers) to validate our silicon chip.  For this we
started with Ubuntu 16.04 LTS v4.4 kernel.

Now all the test boxes which started with 16.04 installation are been
automatically moved on to a 4.13 kernel. With v4.13 kernel, I see the below
mentioned build error, it is due to sigpending method moved from
<linux/sched.h> into <linux/sched/signal.h>



error: implicit declaration of function ‘signal_pending’
[-Werror=implicit-function-declaration]



The below mentioned patch fixes the build issue:



#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0)

#include <linux/sched/signal.h>

#endif



Basically i’m looking for ubuntu disto with N years of  security
support\updates along with supporting\developing our out-of-tree module for
new kernel versions. What would be the best strategy?


>
> > I’d like to know, what are the differences between the main Linux kernel
> > and the kernel being used by Ubuntu?
>
> A given version of Ubuntu takes a specific upstream kernel version and
> adds various extras, which may include extra drivers and backported
> features from later kernel versions.
>
> > If I need to upgrade our drivers to latest kernel v4.17, what are the
> best
> > possible ways? In future, is it possible for us to use the current
> > installed 16.04 LTS by just upgrading the Linux kernel version?
>
> The easiest way to install the latest kernel version onto Ubuntu is to
> use our mainline builds [1]. Understand though that these builds are
> only for testing and will not receive support as far as fixing bugs,
> etc.
>
> > Are all the Linux kernel releases are backward compatible?
>
> In broad strokes yes, as there is a pretty strict policy upstream about
> not introducing regressions to userspace. However sometimes issues do
> slip in, and you might also see problems if you try to install kernel
> packages from a newer Ubuntu release into an older release. The only
> supported way to run newer kernels is through the hwe packages, and
> those are only provided for LTS releases.
>
> Seth
>
>
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