Re: Uses of Linux backports in the industry

Theodore Ts'o
2015-05-29T17:36:27Z

On Fri, May 29, 2015 at 05:01:00PM +0200, Richard Weinberger wrote:
> On Fri, May 29, 2015 at 4:53 PM, Enrico Weigelt, metux IT consult
> <weigelt@melag.de> wrote:
> > Am 29.05.2015 um 04:54 schrieb Luis R. Rodriguez:
> > Actually, I really wonder why folks are sticking to ancient kernels on
> > newer hardware.
>
> Enterprise distribution kernels. Or "special" kernels like PREEMPT_RT.
> Sometimes the vendor BSP is that horrid that a customer cannot afford
> to forward port it
> but wants recent stuff. So you need to backport...

Yep. The technique I used for the backporting ext4 encryption into
the 3.10 android-common git tree in AOSP was to drop in the 3.18
versions of fs/ext4 and fs/jbd2 into the 3.10 tree (along with the
associaed include files in include/linux and include/trace/events, of
course), and then fix things up until they built correctly (using
cherry-picks and in some cases, reverting some changes in the 3.18
version of fs/ext4). After I was sure the transplant of the 3.18
version of ext4 had "taken" correctly, with no test regressions, only
then did I cherry-pick all of the ext4 encryption changes on top of
3.10.

The backport of ext4 encryption to the 3.18 version of android-common
should be much easier. :-) Unfortunately, I also have to do a
backport to the 3.14 android-common branch as well. <sigh>

Yes, it's ugly, but there still are some SOC and drivers that aren't
available on newer kernels. Basically, the handset vendors need to
lean a lot harder on the SOC and other peripheral (cell radios, GPS,
etc., etc.). :-(

- Ted