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

NeilBrown
2012-04-26T06:31:57Z

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

> From: Rafael J. Wysocki <rjw@sisk.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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