linux-kernel - Re: [PATCH v3] usb/hcd: Send a uevent signaling that the host controller had died

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Date:   Thu, 18 Apr 2019 08:51:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Guenter Roeck <groeck@...gle.com>
Cc:     Raul Rangel <rrangel@...omium.org>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-usb@...r.kernel.org, Guenter Roeck <groeck@...omium.org>,
        Oliver Neukum <oneukum@...e.com>,
        Daniel Kurtz <djkurtz@...omium.org>, zwisler@...omium.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Dmitry Torokhov <dtor@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Johan Hovold <johan@...nel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: Re: [PATCH v3] usb/hcd: Send a uevent signaling that the host
 controller had died

On Wed, Apr 17, 2019 at 04:20:09PM -0700, Guenter Roeck wrote:
> On Wed, Apr 17, 2019 at 3:41 PM Raul Rangel <rrangel@...omium.org> wrote:
> >
> > On Wed, Apr 17, 2019 at 03:23:52PM -0700, Guenter Roeck wrote:
> > > On Wed, Apr 17, 2019 at 3:11 PM Raul Rangel <rrangel@...omium.org> wrote:
> > > >
> > > > On Wed, Apr 17, 2019 at 04:39:23PM -0400, Alan Stern wrote:
> > > > >
> > > > > This sounds like a golden opportunity!  Submit a separate patch making
> > > > > the parameter to kobject_uevent_env be const (actually const char *
> > > > > const []), then submit this patch on top of that one.
> > > > So there are other parts of the code base that dynamically create their
> > > > array values. So by making the function take const, it breaks :(
> > >
> > > Confused. The calling code can still be non-const. I don't see the
> > > parameter modified in kobject_uevent_env(), so declaring it const
> > > should be possible. Can you give an example of code that no longer
> > > works ?
> > static int notify_user_space(struct thermal_zone_device *tz, int trip)
> > {
> >         char *thermal_prop[5];
> >         int i;
> >
> >         mutex_lock(&tz->lock);
> >         thermal_prop[0] = kasprintf(GFP_KERNEL, "NAME=%s", tz->type);
> >         thermal_prop[1] = kasprintf(GFP_KERNEL, "TEMP=%d", tz->temperature);
> >         thermal_prop[2] = kasprintf(GFP_KERNEL, "TRIP=%d", trip);
> >         thermal_prop[3] = kasprintf(GFP_KERNEL, "EVENT=%d", tz->notify_event);
> >         thermal_prop[4] = NULL;
> >         kobject_uevent_env(&tz->device.kobj, KOBJ_CHANGE, thermal_prop);
> >         for (i = 0; i < 4; ++i)
> >                 kfree(thermal_prop[i]);
> >         mutex_unlock(&tz->lock);
> >         return 0;
> > }
> >
> > drivers/thermal/user_space.c:48:52: error: passing 'char *[5]' to parameter of type 'const char *const *' discards qualifiers in nested pointer types [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
> >         kobject_uevent_env(&tz->device.kobj, KOBJ_CHANGE, thermal_prop);
> >                                                           ^~~~~~~~~~~~
> > include/linux/kobject.h:238:22: note: passing argument to parameter 'envp' here
> >                         const char *const envp[]);
> >                                           ^
> >
> > http://c-faq.com/ansi/constmismatch.html explains why it fails.
> >
> Interesting. One never stops learning. So the best you could do would
> be char * const envp[], but I guess that doesn't help much.

Yeah, I went down this path a year or so ago and had to give it up as
well :(