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From:   Tri Vo <trong@android.com>
Date:   Sat, 3 Aug 2019 15:40:03 -0700
Message-ID: <CANA+-vDYh4a74ve1NZkybbcqpQZK-8tTGVK6+Nqgv0yvqg-Dgg@mail.gmail.com>
Subject: Re: [PATCH v6] PM / wakeup: show wakeup sources stats in sysfs
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Stephen Boyd <swboyd@chromium.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Hridya Valsaraju <hridya@google.com>,
        Sandeep Patil <sspatil@google.com>,
        Kalesh Singh <kaleshsingh@google.com>,
        Ravi Chandra Sadineni <ravisadineni@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>
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On Thu, Aug 1, 2019 at 3:10 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Aug 1, 2019 at 11:45 PM Tri Vo <trong@android.com> wrote:
> >
> > On Thu, Aug 1, 2019 at 1:23 PM Stephen Boyd <swboyd@chromium.org> wrote:
> > >
> > > Quoting Tri Vo (2019-08-01 12:50:25)
> > > > On Wed, Jul 31, 2019 at 4:45 PM Stephen Boyd <swboyd@chromium.org> wrote:
> > > > >
> > > > > Quoting Rafael J. Wysocki (2019-07-31 16:10:38)
> > > > > > On Thu, Aug 1, 2019 at 12:59 AM Tri Vo <trong@android.com> wrote:
> > > > > > >
> > > > > > > >
> > > > > > > > So why wouldn't something like this suffice:
> > > > > > > >
> > > > > > > > dev = device_create_with_groups(wakeup_class, parent, MKDEV(0, 0), ws,
> > > > > > > >                                 wakeup_source_groups, "wakeup:%s", ws->name);
> > > > > > > >
> > > > > > > > ?
> > > > > > >
> > > > > > > ws->name is inherited from the device name. IIUC device names are not
> > > > > > > guaranteed to be unique. So if different devices with the same name
> > > > > > > register wakeup sources, there is an error.
> > > > > >
> > > > > > OK
> > > > > >
> > > > > > So I guess the names are retained for backwards compatibility with
> > > > > > existing user space that may be using them?
> > > > > >
> > > > > > That's kind of fair enough, but having two different identification
> > > > > > schemes for wakeup sources will end up confusing.
> > > > >
> > > > > I understand your concern about the IDA now. Thanks for clarifying.
> > > > >
> > > > > How about we name the devices 'wakeupN' with the IDA when they're
> > > > > registered with a non-NULL device pointer and then name them whatever
> > > > > the name argument is when the device pointer is NULL. If we have this,
> > > > > we should be able to drop the name attribute in sysfs and figure out the
> > > > > name either by looking at the device name in /sys/class/wakeup/ if it
> > > > > isn't 'wakeupN', or follow the symlink to the device in /sys/devices/
> > > > > and look at the parent device name there.
> > > >
> > > > This makes it difficult for userspace to query the name a wakeup
> > > > source, as it now has to first figure out if a wakeup source is
> > > > associated with a device or not. The criteria for that is also
> > > > awkward, userspase has to check if directory path contains "wakeupN",
> > > > then it's a virtual wakeup source.
> > >
> > > I think you mean if it doesn't match wakeupN then it's a virtual wakeup
> > > source?
> >
> > Yes
> > >
> > > >
> > > > IMO it's cleaner to consistently have /sys/class/wakeup/wakeupN/name
> > > > for every wakeup source.
> > >
> > > I don't find it awkward or difficult. Just know what the name of the
> > > /sys/class/wakeup/ path is and then extract the name from there if it
> > > doesn't match wakeupN, otherwise read the 'device' symlink and run it
> > > through basename.
> >
> > The concern was that having both "id" and "name" around might be
> > confusing. I don't think that making the presence of "name"
> > conditional helps here. And we have to maintain additional logic in
> > both kernel and userspace to support this.
> >
> > Also, say, userspace grabs a wakelock named "wakeup0". In the current
> > patch, this results in a name collision and an error. Even assuming
> > that userspace doesn't have ill intent, it still needs to be aware of
> > "wakeupN" naming pattern to avoid this error condition.
> >
> > All wakeup sources in the /sys/class/wakeup/ are in the same namespace
> > regardless of where they originate from, i.e. we have to either (1)
> > inspect the name of a wakeup source and make sure it's unique before
> > using it as a directory name OR (2) generate the directory name on
> > behalf of whomever is registering a wakeup source, which I think is a
> > much simpler solution.
>
> OK, whatever.
>
> Let's use the IDA as originally proposed and retain the names for
> backwards compatibility only.
>
> Maybe just allocate the ID at the wakeup source object creation time
> already (ISTR that you did that before attempting to create a virtual
> device for the wakeup source).

Yes, allocating the ID when creating the wakeup source object makes
sense. However, kernel/power/wakelock.c allocates its wakeup sources
manually. I imagine we don't want these IDs to be created in more than
one place.

Making wakelock.c only use wakeup_source_*() family of functions when
dealing with wakeup sources  might be a worthwhile change though. Then
we won't have to worry about ID allocation in wakelock.c. WDYT?

Also, it sounds like we all agree with "/sys/class/wakeup/wsN/" path
and "/sys/class/wakeup/wsN/name" attribute for each wakeup source,
right?