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From:   Gabriel C <nix.or.die@gmail.com>
Date:   Mon, 24 Dec 2018 08:31:27 +0100
Message-ID: <CAEJqkgjSX8PW-NXa8CoMzx=2P5LOiDz0MCHoZ03zE7wZ=n2dKg@mail.gmail.com>
Subject: Re: FYI: Userland breakage caused by udev bind commit
To:     Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc:     Christian Brauner <christian@brauner.io>,
        Marcus Meissner <christian.brauner@canonical.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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Am So., 23. Dez. 2018 um 19:09 Uhr schrieb Dmitry Torokhov
<dmitry.torokhov@gmail.com>:

[ also added Linus to CC on that one too ]
>
> On Sun, Dec 23, 2018 at 06:17:04PM +0100, Christian Brauner wrote:
> > On Sun, Dec 23, 2018 at 05:49:54PM +0100, Marcus Meissner wrote:
> > > Hi,
> > >
> > > I am the maintainer of libmtp and libgphoto2
> > >
> > > Some months ago I was made aware of this bug:
> > >     https://bugs.kde.org/show_bug.cgi?id=387454
> > >
> > > This was fallout identified to come from this kernel commit:
> > >
> > >     commit 1455cf8dbfd06aa7651dcfccbadb7a093944ca65
> > >     Author: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > >     Date:   Wed Jul 19 17:24:30 2017 -0700
> >
> > Fwiw, the addition of {un}bind events has caused issues for
> > systemd-udevd as well and is tracked here:
> > https://github.com/systemd/systemd/issues/7587
> > I haven't been aware of this until yesterday and it seems that so far
> > this hasn't been brought up on lkml until you did now.
>
> The fallout was caused by premature enabling of the new events in
> systemd/udev by yours truly (even though the commit has Lennart's name
> on it due to how it was merged):
>
> https://github.com/systemd/systemd/commit/9a39e1ce314d1a6f8a754f6dab040019239666a9
>
> "Add handling for bind/unbind actions (#6720)
>
> Newer kernels will emit uevents with "bind" and "unbind" actions. These
> uevents will be issued when driver is bound to or unbound from a device.
> "Bind" events are helpful when device requires a firmware to operate
> properly, and driver is unable to create a child device before firmware
> is properly loaded.
>
> For some reason systemd validates actions and drops the ones it does not
> know, instead of passing them on through as old udev did, so we need to
> explicitly teach it about them."
>
> Similarly it is now papered over in systemd/udev until we make it
> properly handle new events:
>
> https://github.com/systemd/systemd/commit/56c886dc7ed5b2bb0882ba85136f4070545bfc1b
>
> "sd-device: ignore bind/unbind events for now
>
> Until systemd/udev are ready for the new events and do not flush entire
> device state on each new event received, we should ignore them."
>

And how about peoples still uses systemd < 235 and newer kernels ?

> > >
> > > If distributions would be using libmtp and libgphoto2 udev rules
> > > that just triggered on "add" events, and not the new "bind" events,
> > > the missing "attribute tagging" of the "bind" events would confused the
> > > KDE Solid device detection and make the devices no longer detected.
> > >
> > > This did not affect distributions that rely on the newer "hwdb"
> > > device detection method.
> > >
> > > I have released fixed libmtp and libgphoto2 versions in November, so
> > > this is under control, but wanted to bring this up as a "kernel caused
> > > userland breakage".
>
> Given that we explicitly enabled these new events in systemd/udev code
> this is actually "userspace caused userspace breakage" case.

I really do not agree with you here .. Is kernel -> userspace breakage
and while userspace is trying to workaround even much more breaks.

>
> Still it is unfortunate that we did nit notice that my patch enabling
> this functionality in systemd was premature.
>
> Thanks.
>
> --
> Dmitry

BR,

Gabriel