linux-kernel - Re: [RFC][PATCH 8/8] PM / Sleep: Add user space interface for manipulating wakeup sources

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Date:	Thu, 26 Apr 2012 16:31:43 +1000
From:	NeilBrown <neilb@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	John Stultz <johnstul@...ibm.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>, markgross@...gnar.org,
	Matthew Garrett <mjg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Brian Swetland <swetland@...gle.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 8/8] PM / Sleep: Add user space interface for
 manipulating wakeup sources

On Tue, 24 Apr 2012 23:27:17 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> Subject: PM / Sleep: Add user space interface for manipulating wakeup sources, v2
> 
> Android allows user space to manipulate wakelocks using two
> sysfs file located in /sys/power/, wake_lock and wake_unlock.
> Writing a wakelock name and optionally a timeout to the wake_lock
> file causes the wakelock whose name was written to be acquired (it
> is created before is necessary), optionally with the given timeout.
> Writing the name of a wakelock to wake_unlock causes that wakelock
> to be released.
> 
> Implement an analogous interface for user space using wakeup sources.
> Add the /sys/power/wake_lock and /sys/power/wake_unlock files
> allowing user space to create, activate and deactivate wakeup
> sources, such that writing a name and optionally a timeout to
> wake_lock causes the wakeup source of that name to be activated,
> optionally with the given timeout.  If that wakeup source doesn't
> exist, it will be created and then activated.  Writing a name to
> wake_unlock causes the wakeup source of that name, if there is one,
> to be deactivated.  Wakeup sources created with the help of
> wake_lock that haven't been used for more than 5 minutes are garbage
> collected and destroyed.  Moreover, there can be only WL_NUMBER_LIMIT
> wakeup sources created with the help of wake_lock present at a time.
> 
> The data type used to track wakeup sources created by user space is
> called "struct wakelock" to indicate the origins of this feature.
> 
> This version of the patch includes an rbtree manipulation fix from John Stultz.

Looks good.  Just a couple of minor suggestions.


> +ssize_t pm_show_wakelocks(char *buf, bool show_active)
> +{
> +	struct rb_node *node;
> +	struct wakelock *wl;
> +	char *str = buf;
> +	char *end = buf + PAGE_SIZE;
> +
> +	mutex_lock(&wakelocks_lock);
> +
> +	for (node = rb_first(&wakelocks_tree); node; node = rb_next(node)) {
> +		bool active;
> +
> +		wl = rb_entry(node, struct wakelock, node);
> +		spin_lock_irq(&wl->ws.lock);
> +		active = wl->ws.active;
> +		spin_unlock_irq(&wl->ws.lock);

I don't think the spin_lock is needed.  We are just reading one value and it
is either 0 or not.  So there is no possibility for any inconsistency.
                if (wl->ws.active == show_active)
?

> +		if (active == show_active)
> +			str += scnprintf(str, end - str, "%s ", wl->name);

Arg.  Extra space on the end of the line!!  :-)

I would suggest the entries be terminated by '\n' rather than separate by
space.
one-item-per-line is much more common in Unix in general.  'grep' allows
you to find things more easily etc.
   while read a
   do echo $a > wake_unlock
   done < wake_lock



> +	}
> +	str += scnprintf(str, end - str, "\n");
> +
> +	mutex_unlock(&wakelocks_lock);
> +	return (str - buf);
> +}
> +


Thanks,
NeilBrown

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