linux-kernel - Re: [PATCH] powerpc/vio: use simple dummy struct device as bus parent

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Message-ID: <CAOZ2QJNNnkM_0ZTULHOYGY2wEz1GxZWzHjosnM=j98zxZXUvYA@mail.gmail.com>
Date:   Fri, 27 Sep 2019 15:48:49 -0400
From:   Dan Streetman <ddstreet@...onical.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/vio: use simple dummy struct device as bus parent

On Fri, Sep 27, 2019 at 2:19 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Fri, Sep 27, 2019 at 09:04:02AM -0400, Dan Streetman wrote:
> > The dummy vio_bus_device creates the /sys/devices/vio directory, which
> > contains real vio devices under it; since it represents itself as having
> > a bus = &vio_bus_type, its /sys/devices/vio/uevent does call the bus's
> > .uevent function, vio_hotplug(), and as that function won't find a real
> > device for the dummy vio_dev, it will return -ENODEV.
> >
> > One of the main users of the uevent node is udevadm, e.g. when it is called
> > with 'udevadm trigger --devices'.  Up until recently, it would ignore any
> > errors returned when writing to devices' uevent file, but it was recently
> > changed to start returning error if it gets an error writing to any uevent
> > file:
> > https://github.com/systemd/systemd/commit/97afc0351a96e0daa83964df33937967c75c644f
> >
> > since the /sys/devices/vio/uevent file has always returned ENODEV from
> > any write to it, this now causes the udevadm trigger command to return
> > an error.  This may be fixed in udevadm to ignore ENODEV errors, but the
> > vio driver should still be fixed.
> >
> > This patch changes the arch/powerpc/platform/pseries/vio.c 'dummy'
> > parent device into a real dummy device with no .bus, so its uevent
> > file will stop returning ENODEV and simply do nothing and return 0.
> >
> > Signed-off-by: Dan Streetman <ddstreet@...onical.com>
> > ---
> >  arch/powerpc/platforms/pseries/vio.c | 11 ++++-------
> >  1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/powerpc/platforms/pseries/vio.c b/arch/powerpc/platforms/pseries/vio.c
> > index 79e2287991db..63bc16631680 100644
> > --- a/arch/powerpc/platforms/pseries/vio.c
> > +++ b/arch/powerpc/platforms/pseries/vio.c
> > @@ -32,11 +32,8 @@
> >  #include <asm/page.h>
> >  #include <asm/hvcall.h>
> >
> > -static struct vio_dev vio_bus_device  = { /* fake "parent" device */
> > -     .name = "vio",
> > -     .type = "",
> > -     .dev.init_name = "vio",
> > -     .dev.bus = &vio_bus_type,
> > +static struct device vio_bus = {
> > +     .init_name      = "vio",
>
> Eeek, no!  Why are you creating a static device that will then be
> reference counted?  Not nice :(

sorry!  I'll admit that I simply copied what drivers/base/platform.c
seemed to be doing.

>
> What's wrong with a simple call to device_create() for your "fake"
> device you want to make here?  That's what it is there for :)

ack, will send a new patch using that.  thanks!

>
> thanks,
>
> greg k-h