question about one of your ubuntu patch

[Juerg Haefliger]

On Tue, 11 Aug 2020 12:49:49 -0700
David Lee <saynice111 at gmail.com> wrote:

> Hi,
> 
> Thanks for your reply. Very helpful to me.
> 
> There is no upstream Linux 4.15 stable branch.

Yes there is:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/?h=linux-4.15.y


> There is no upstream linux 4.15 long term support branch. But there is a
> Linux stable branch
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/?h=linux-4.15.y

Yes, what I said above.


> 
> Ubuntu's bionic is based on Linux 4.15. But there is also linux 4.15-linux
> 4.15.18 branch in ubuntu-bionic.

There is no such branch in bionic:
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/bionic


> And commits in Linux 4.15-4.15.18 in
> ubuntu git is the same as it in Linux git except some ubuntu sauce patches.

Bionic 4.15 contains all the commits from upstream 4.15.18 plus some more.

 
> Besides, how does ubuntu know if there is a new patch added in upstream?
> And how do ubuntu determine if a patch is necessary for ubuntu?

We monitor the two closest upstream LTS kernels, 4.14 and 4.19 in this case.
And we periodically pull in commits from those two stable kernels into bionic
4.15. We might end up pulling in commits that we don't really care about
(because of configs we don't have enabled or architectures we don't support,
or...) and sometimes we drop stable commits if they required substantial back-
or forward-porting, unless we have clear evidence (bug reports) that they're
absolutely needed/required.

...Juerg



> Thanks
> 
> On Tue, Aug 11, 2020 at 4:32 AM Thadeu Lima de Souza Cascardo <
> cascardo at canonical.com> wrote:  
> 
> > On Tue, Aug 11, 2020 at 12:33:17AM -0700, David Lee wrote:  
> > > Hi,
> > >
> > > I saw your email in the patch "serdev: Fix serdev_uevent failure on ACPI
> > > enumerated serdev-controllers 586ca5b1a90b66eb0a2805c9419683e33d1d418b"  
> > in  
> > > ubuntu's git repository.
> > > I am surprised to find that this patch in ubuntu git is committed on Apr  
> > 12  
> > > 10:06:37 2018. But this patch is committed to linux 4.15 stable branch
> > > on Apr 12 12:31:11 2018.
> > > In ubuntu git repository, this patch is also in Linux 4.15 stable branch.
> > > Why a patch is committed before it's added in Linux 4.15 stable branch?
> > >
> > > Thanks  
> >
> > Hi, David.
> >
> > There is no upstream Linux 4.15 stable branch. Upstream kernel.org git
> > trees
> > closest to 4.15 are 4.14 and 4.19. Kamal Mostafa, from the Ubuntu Kernel
> > team
> > picks up commits from those trees in order to apply them to Ubuntu bionic
> > kernel tree, which is based on 4.15. As upstream has stopped publishing
> > updates
> > to 4.15 and Ubuntu picked up 4.15 for its Bionic release, we have Kamal do
> > the
> > great job of tracking commits to 4.14 and 4.19 and make pull requests so
> > those
> > can be included in Ubuntu's kernel.
> >
> > But patches are also submitted to Ubuntu's kernel through other ways and
> > for
> > other reasons, like when they fix specific bugs tracked at launchpad. It
> > may
> > happen that such patches match upstream commits that have both landed on
> > Kamal's tree and directly on Ubuntu's tree.
> >
> > And by git's distributed nature, the same patch may be applied on different
> > dates, or it may happen that they are rebased or reapplied, causing them to
> > have different commit ids, and even different commit dates or commit
> > authors,
> > or have had their messages changed because of sign-offs.
> >
> > I didn't investigate the specific case you pointed out, but it may be that
> > with
> > the explanations above, you may find other differences between those two
> > commits that might explain what might have happened.
> >
> > Regards.
> > Thadeu Cascardo.
> >  

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