Re: [Ksummit-discuss] [MAINTAINER SUMMIT] Distribution kernel bugzillas considered harmful

[Jan Kara <jack@suse.cz>]

On Wed 19-09-18 08:31:04, Takashi Iwai wrote:
> On Wed, 19 Sep 2018 08:16:17 +0200,
> Geert Uytterhoeven wrote:
> > 
> > Hi Iwai-san,
> > 
> > On Tue, Sep 18, 2018 at 10:37 PM Takashi Iwai <tiwai@suse.de> wrote:
> > > On Tue, 18 Sep 2018 15:43:08 +0200,
> > > Martin K. Petersen wrote:
> > > > Sorry I'm a little late to the game here. Been out on vacation.
> > > >
> > > > > We order patches in our trees in the same git-topological-ordering as they
> > > > > are upstream. It has a lot of benefits, most importantly: it doesn't
> > > > > introduce artificial conflicts that don't exist in reality.
> > > > >
> > > > > In order to achieve that, we of course need 1:1 mapping between our
> > > > > patches and upstream commits.  Rebases destroy that mapping.
> > > > >
> > > > > And in some areas (scsi is one, but not the only one), we basically had no
> > > > > other choice than considering maintainer's tree to be already "upstream
> > > > > enough", without waiting for Linus' tree merge.
> > > >
> > > > When I discussed this with Johannes a little while ago, I suggested you
> > > > guys used git patch-id to track patches instead of commit ids. That's
> > > > how we track patches applied across many different trees internally.
> > > > Works much better than using the upstream sha.
> > >
> > > What is git patch id?  Is there any internal patch tag?
> > 
> > It's the output of "git patch-id", which is a hash of the patch, without
> > including its dependencies.  This allows to match identical commits in
> > different branches, and is what "git cherry" and "git rebase" use to detect
> > already applied patches.
> > 
> > Example (from v4.18.y):
> > 
> > $ git show -s e496c9a4c17d4a97ed8d222f368f3b8ad8133fb9
> > commit e496c9a4c17d4a97ed8d222f368f3b8ad8133fb9
> > Author: Robert Munteanu <rombert@apache.org>
> > Date:   Tue Jun 19 11:20:40 2018 +0300
> > 
> >     HID: redragon: fix num lock and caps lock LEDs
> > 
> >     commit dc9b8e85ed95cbe7e3ad0eabb5b48d617bbc365e upstream.
> > 
> >     The redragon asura keyboard registers two input devices. The initial commit
> >     85455dd906d5 ("HID: redragon: Fix modifier keys for Redragon Asura
> > Keyboard")
> >     considered this an error and prevented one of the devices from registering.
> >     However, once this is done the num lock and caps lock leds no
> > longer toggle on
> >     and off, although the key functionality is not affected.
> > 
> >     This commit removes the code that prevents the input device
> >     registration and restores the num lock and caps lock LEDs.
> > 
> >     Fixes: 85455dd906d5 ("HID: redragon: Fix modifier keys for
> > Redragon Asura Keyboard")
> >     Signed-off-by: Robert Munteanu <rombert@apache.org>
> >     Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> >     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > 
> > $ git show e496c9a4c17d4a97ed8d222f368f3b8ad8133fb9 | git patch-id
> > 9d4546a92b459de7249748c0a38b50c989f13bd1
> > e496c9a4c17d4a97ed8d222f368f3b8ad8133fb9
> > $ git show dc9b8e85ed95cbe7e3ad0eabb5b48d617bbc365e | git patch-id
> > 9d4546a92b459de7249748c0a38b50c989f13bd1
> > dc9b8e85ed95cbe7e3ad0eabb5b48d617bbc365e
> > 
> > So both commits are identical, as they have the same patch ID.
> 
> Thanks for the explanation!
> 
> This would help for identifying the rebased patch, yes.  But it still
> doesn't help for sorting as is.  You cannot get the topology
> information from the patch id, so you don't know the patch order,
> either.  (You can deduce the actual commit from the patch id, but it's
> too heavy if you have 20,000 patches :)

Actually we could use the patch id to identify new commit id of a rebased
patch and infer proper ordering once we have the new commit id. So I think
using patch id (additionally to commit id) would really help us and solve
95% of rebases of e.g. SCSI tree by our automation without human
interaction.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR