[RFC 0/2] clocksource: don't suspend/resume when unused

[RFC 0/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

Hi,

This is a quite naive implementation to track whether a cloccksource is enabled.
I chose not to add a member in struct clocksource and use a flag instead.

I found that timekeeping.c is the only consumer for clocksource and I converted
it to use clocksource_enable and clocksource_disable.

Regards,

Alexandre Belloni (2):
  clocksource: track usage
  clocksource: don't suspend/resume when unused

 include/linux/clocksource.h |  4 ++++
 kernel/time/clocksource.c   | 30 ++++++++++++++++++++++++++++--
 kernel/time/timekeeping.c   |  8 +++-----
 3 files changed, 35 insertions(+), 7 deletions(-)

-- 
2.1.0

[RFC 1/2] clocksource: track usage

[Alexandre Belloni]

Track whether the clocksource is enabled or disabled.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 include/linux/clocksource.h |  4 ++++
 kernel/time/clocksource.c   | 26 ++++++++++++++++++++++++++
 kernel/time/timekeeping.c   |  8 +++-----
 3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index abcafaa20b86..7735902fc5f6 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -210,6 +210,8 @@ struct clocksource {
 #define CLOCK_SOURCE_SUSPEND_NONSTOP		0x80
 #define CLOCK_SOURCE_RESELECT			0x100
 
+#define CLOCK_SOURCE_USED			0x200
+
 /* simplify initialization of mask field */
 #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
 
@@ -282,6 +284,8 @@ static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
 
 extern int clocksource_register(struct clocksource*);
 extern int clocksource_unregister(struct clocksource*);
+extern int clocksource_enable(struct clocksource *);
+extern void clocksource_disable(struct clocksource *);
 extern void clocksource_touch_watchdog(void);
 extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index b79f39bda7e1..920a4da58eb0 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -889,6 +889,32 @@ int clocksource_unregister(struct clocksource *cs)
 }
 EXPORT_SYMBOL(clocksource_unregister);
 
+/**
+ * clocksource_enable - enable a registered clocksource
+ * @cs:	clocksource to enable
+ */
+int clocksource_enable(struct clocksource *cs)
+{
+	cs->flags |= CLOCK_SOURCE_USED;
+	if (cs->enable)
+		return cs->enable(cs);
+
+	return 0;
+}
+EXPORT_SYMBOL(clocksource_enable);
+
+/**
+ * clocksource_disable - disable a registered clocksource
+ * @cs:	clocksource to disable
+ */
+void clocksource_disable(struct clocksource *cs)
+{
+	cs->flags &= ~CLOCK_SOURCE_USED;
+	if (cs->disable)
+		cs->disable(cs);
+}
+EXPORT_SYMBOL(clocksource_disable);
+
 #ifdef CONFIG_SYSFS
 /**
  * sysfs_show_current_clocksources - sysfs interface for current clocksource
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6a931852082f..1c6ffd3d068c 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -915,11 +915,10 @@ static int change_clocksource(void *data)
 	 * for built-in code (owner == NULL) as well.
 	 */
 	if (try_module_get(new->owner)) {
-		if (!new->enable || new->enable(new) == 0) {
+		if (!new->enable || clocksource_enable(new) == 0) {
 			old = tk->tkr.clock;
 			tk_setup_internals(tk, new);
-			if (old->disable)
-				old->disable(old);
+			clocksource_disable(old);
 			module_put(old->owner);
 		} else {
 			module_put(new->owner);
@@ -1080,8 +1079,7 @@ void __init timekeeping_init(void)
 	ntp_init();
 
 	clock = clocksource_default_clock();
-	if (clock->enable)
-		clock->enable(clock);
+	clocksource_enable(clock);
 	tk_setup_internals(tk, clock);
 
 	tk_set_xtime(tk, &now);
-- 
2.1.0

[RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

There is no point in calling suspend/resume for unused
clocksources.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 kernel/time/clocksource.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 920a4da58eb0..baea4e42ae90 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -493,7 +493,7 @@ void clocksource_suspend(void)
 	struct clocksource *cs;
 
 	list_for_each_entry_reverse(cs, &clocksource_list, list)
-		if (cs->suspend)
+		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
 			cs->suspend(cs);
 }
 
@@ -505,7 +505,7 @@ void clocksource_resume(void)
 	struct clocksource *cs;
 
 	list_for_each_entry(cs, &clocksource_list, list)
-		if (cs->resume)
+		if (cs->resume && (cs->flags & CLOCK_SOURCE_USED))
 			cs->resume(cs);
 
 	clocksource_resume_watchdog();
-- 
2.1.0

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Thomas Gleixner]

On Fri, 16 Jan 2015, Alexandre Belloni wrote:

> There is no point in calling suspend/resume for unused
> clocksources.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> ---
>  kernel/time/clocksource.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index 920a4da58eb0..baea4e42ae90 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -493,7 +493,7 @@ void clocksource_suspend(void)
>  	struct clocksource *cs;
>  
>  	list_for_each_entry_reverse(cs, &clocksource_list, list)
> -		if (cs->suspend)
> +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
>  			cs->suspend(cs);

This might be dangerous. If the clocksource has no enable/disable
callbacks, but suspend/resume, then you might leave it enabled across
suspend.

Thanks,

	tglx

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

On 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote :
> On Fri, 16 Jan 2015, Alexandre Belloni wrote:
> 
> > There is no point in calling suspend/resume for unused
> > clocksources.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> > ---
> >  kernel/time/clocksource.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > index 920a4da58eb0..baea4e42ae90 100644
> > --- a/kernel/time/clocksource.c
> > +++ b/kernel/time/clocksource.c
> > @@ -493,7 +493,7 @@ void clocksource_suspend(void)
> >  	struct clocksource *cs;
> >  
> >  	list_for_each_entry_reverse(cs, &clocksource_list, list)
> > -		if (cs->suspend)
> > +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
> >  			cs->suspend(cs);
> 
> This might be dangerous. If the clocksource has no enable/disable
> callbacks, but suspend/resume, then you might leave it enabled across
> suspend.
> 

Isn't that already the case?
Right now, if you call clocksource_suspend, it doesn't matter whether
the clocksource has an enable or not, it will be suspended. Maybe I'm
mistaken but my patch doesn't seem to change that behaviour.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [RFC 1/2] clocksource: track usage

[Boris Brezillon]

Hi Alexandre,

On Fri, 16 Jan 2015 10:17:53 +0100
Alexandre Belloni <alexandre.belloni@free-electrons.com> wrote:

> Track whether the clocksource is enabled or disabled.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> ---
>  include/linux/clocksource.h |  4 ++++
>  kernel/time/clocksource.c   | 26 ++++++++++++++++++++++++++
>  kernel/time/timekeeping.c   |  8 +++-----
>  3 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> index abcafaa20b86..7735902fc5f6 100644
> --- a/include/linux/clocksource.h
> +++ b/include/linux/clocksource.h
> @@ -210,6 +210,8 @@ struct clocksource {
>  #define CLOCK_SOURCE_SUSPEND_NONSTOP		0x80
>  #define CLOCK_SOURCE_RESELECT			0x100
>  
> +#define CLOCK_SOURCE_USED			0x200
> +
>  /* simplify initialization of mask field */
>  #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
>  
> @@ -282,6 +284,8 @@ static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
>  
>  extern int clocksource_register(struct clocksource*);
>  extern int clocksource_unregister(struct clocksource*);
> +extern int clocksource_enable(struct clocksource *);
> +extern void clocksource_disable(struct clocksource *);
>  extern void clocksource_touch_watchdog(void);
>  extern struct clocksource* clocksource_get_next(void);
>  extern void clocksource_change_rating(struct clocksource *cs, int rating);
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index b79f39bda7e1..920a4da58eb0 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -889,6 +889,32 @@ int clocksource_unregister(struct clocksource *cs)
>  }
>  EXPORT_SYMBOL(clocksource_unregister);
>  
> +/**
> + * clocksource_enable - enable a registered clocksource
> + * @cs:	clocksource to enable
> + */
> +int clocksource_enable(struct clocksource *cs)
> +{
> +	cs->flags |= CLOCK_SOURCE_USED;
> +	if (cs->enable)
> +		return cs->enable(cs);

I guess you should check cs->enable() return code before setting the
CLOCK_SOURCE_USED flag.




-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Daniel Lezcano]

On 01/16/2015 11:35 AM, Alexandre Belloni wrote:
> On 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote :
>> On Fri, 16 Jan 2015, Alexandre Belloni wrote:
>>
>>> There is no point in calling suspend/resume for unused
>>> clocksources.
>>>
>>> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
>>> ---
>>>   kernel/time/clocksource.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
>>> index 920a4da58eb0..baea4e42ae90 100644
>>> --- a/kernel/time/clocksource.c
>>> +++ b/kernel/time/clocksource.c
>>> @@ -493,7 +493,7 @@ void clocksource_suspend(void)
>>>   	struct clocksource *cs;
>>>
>>>   	list_for_each_entry_reverse(cs, &clocksource_list, list)
>>> -		if (cs->suspend)
>>> +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
>>>   			cs->suspend(cs);
>>
>> This might be dangerous. If the clocksource has no enable/disable
>> callbacks, but suspend/resume, then you might leave it enabled across
>> suspend.
>>
>
> Isn't that already the case?
> Right now, if you call clocksource_suspend, it doesn't matter whether
> the clocksource has an enable or not, it will be suspended. Maybe I'm
> mistaken but my patch doesn't seem to change that behaviour.

Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED 
will be never set, hence the condition will always fail and the suspend 
callback won't be called.


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Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

Hi,

On 16/01/2015 at 11:39:16 +0100, Daniel Lezcano wrote :
> >Isn't that already the case?
> >Right now, if you call clocksource_suspend, it doesn't matter whether
> >the clocksource has an enable or not, it will be suspended. Maybe I'm
> >mistaken but my patch doesn't seem to change that behaviour.
> 
> Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED
> will be never set, hence the condition will always fail and the suspend
> callback won't be called.
> 

It is set in clocksource_enable/disable, even if there is no
enable/disable callback. I only found direct calls to ->enable() in
timekeeper.c, did I miss some?

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Daniel Lezcano]

On 01/16/2015 11:48 AM, Alexandre Belloni wrote:
> Hi,
>
> On 16/01/2015 at 11:39:16 +0100, Daniel Lezcano wrote :
>>> Isn't that already the case?
>>> Right now, if you call clocksource_suspend, it doesn't matter whether
>>> the clocksource has an enable or not, it will be suspended. Maybe I'm
>>> mistaken but my patch doesn't seem to change that behaviour.
>>
>> Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED
>> will be never set, hence the condition will always fail and the suspend
>> callback won't be called.
>>
>
> It is set in clocksource_enable/disable, even if there is no
> enable/disable callback.

Ah, right. But shouldn't we set the flag only if the callback is present 
and succeed as Boris mentioned it ?

> I only found direct calls to ->enable() in
> timekeeper.c, did I miss some?




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Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

On 16/01/2015 at 11:59:33 +0100, Daniel Lezcano wrote :
> On 01/16/2015 11:48 AM, Alexandre Belloni wrote:
> >Hi,
> >
> >On 16/01/2015 at 11:39:16 +0100, Daniel Lezcano wrote :
> >>>Isn't that already the case?
> >>>Right now, if you call clocksource_suspend, it doesn't matter whether
> >>>the clocksource has an enable or not, it will be suspended. Maybe I'm
> >>>mistaken but my patch doesn't seem to change that behaviour.
> >>
> >>Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED
> >>will be never set, hence the condition will always fail and the suspend
> >>callback won't be called.
> >>
> >
> >It is set in clocksource_enable/disable, even if there is no
> >enable/disable callback.
> 
> Ah, right. But shouldn't we set the flag only if the callback is present and
> succeed as Boris mentioned it ?
> 

What Boris was suggesting was that if the enable exist, set it only if
it succeed. Which gives something like that:

int clocksource_enable(struct clocksource *cs)
{
	int ret = 0;

	if (cs->enable)
		ret = cs->enable(cs);

	if (!ret)
		cs->flags |= CLOCK_SOURCE_USED;

	return 0;
}

I will use that version in v2.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Russell King - ARM Linux]

On Fri, Jan 16, 2015 at 11:35:30AM +0100, Alexandre Belloni wrote:
> On 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote :
> > On Fri, 16 Jan 2015, Alexandre Belloni wrote:
> > 
> > > There is no point in calling suspend/resume for unused
> > > clocksources.
> > > 
> > > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> > > ---
> > >  kernel/time/clocksource.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > > index 920a4da58eb0..baea4e42ae90 100644
> > > --- a/kernel/time/clocksource.c
> > > +++ b/kernel/time/clocksource.c
> > > @@ -493,7 +493,7 @@ void clocksource_suspend(void)
> > >  	struct clocksource *cs;
> > >  
> > >  	list_for_each_entry_reverse(cs, &clocksource_list, list)
> > > -		if (cs->suspend)
> > > +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
> > >  			cs->suspend(cs);
> > 
> > This might be dangerous. If the clocksource has no enable/disable
> > callbacks, but suspend/resume, then you might leave it enabled across
> > suspend.
> > 
> 
> Isn't that already the case?
> Right now, if you call clocksource_suspend, it doesn't matter whether
> the clocksource has an enable or not, it will be suspended. Maybe I'm
> mistaken but my patch doesn't seem to change that behaviour.

You change an "always suspend" problem to a "never suspend" problem
since those clocksources which are used, but do not have an ->enable
callback will not be marked with CLOCK_SOURCE_USED.

Look at patch 1:

-               if (!new->enable || new->enable(new) == 0) {
+               if (!new->enable || clocksource_enable(new) == 0) {

If new->enable is NULL, clocksource_enable() won't be called, which
means there's nothing which sets CLOCK_SOURCE_USED, which in turn
means that ->suspend() will never be called.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

On 16/01/2015 at 11:23:24 +0000, Russell King - ARM Linux wrote :
> On Fri, Jan 16, 2015 at 11:35:30AM +0100, Alexandre Belloni wrote:
> > On 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote :
> > > On Fri, 16 Jan 2015, Alexandre Belloni wrote:
> > > 
> > > > There is no point in calling suspend/resume for unused
> > > > clocksources.
> > > > 
> > > > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> > > > ---
> > > >  kernel/time/clocksource.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > > > index 920a4da58eb0..baea4e42ae90 100644
> > > > --- a/kernel/time/clocksource.c
> > > > +++ b/kernel/time/clocksource.c
> > > > @@ -493,7 +493,7 @@ void clocksource_suspend(void)
> > > >  	struct clocksource *cs;
> > > >  
> > > >  	list_for_each_entry_reverse(cs, &clocksource_list, list)
> > > > -		if (cs->suspend)
> > > > +		if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED))
> > > >  			cs->suspend(cs);
> > > 
> > > This might be dangerous. If the clocksource has no enable/disable
> > > callbacks, but suspend/resume, then you might leave it enabled across
> > > suspend.
> > > 
> > 
> > Isn't that already the case?
> > Right now, if you call clocksource_suspend, it doesn't matter whether
> > the clocksource has an enable or not, it will be suspended. Maybe I'm
> > mistaken but my patch doesn't seem to change that behaviour.
> 
> You change an "always suspend" problem to a "never suspend" problem
> since those clocksources which are used, but do not have an ->enable
> callback will not be marked with CLOCK_SOURCE_USED.
> 
> Look at patch 1:
> 
> -               if (!new->enable || new->enable(new) == 0) {
> +               if (!new->enable || clocksource_enable(new) == 0) {
> 
> If new->enable is NULL, clocksource_enable() won't be called, which
> means there's nothing which sets CLOCK_SOURCE_USED, which in turn
> means that ->suspend() will never be called.
> 

My mistake, I should have remove the check, this should be:
	if (clocksource_enable(new) == 0)

And I'll do the change suggested by Boris which should solve that
issue.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [RFC 2/2] clocksource: don't suspend/resume when unused

[Alexandre Belloni]

On 16/01/2015 at 12:07:42 +0100, Alexandre Belloni wrote :
> On 16/01/2015 at 11:59:33 +0100, Daniel Lezcano wrote :
> > On 01/16/2015 11:48 AM, Alexandre Belloni wrote:
> > >Hi,
> > >
> > >On 16/01/2015 at 11:39:16 +0100, Daniel Lezcano wrote :
> > >>>Isn't that already the case?
> > >>>Right now, if you call clocksource_suspend, it doesn't matter whether
> > >>>the clocksource has an enable or not, it will be suspended. Maybe I'm
> > >>>mistaken but my patch doesn't seem to change that behaviour.
> > >>
> > >>Actually, if there is no enable/disable callback, then CLOCK_SOURCE_USED
> > >>will be never set, hence the condition will always fail and the suspend
> > >>callback won't be called.
> > >>
> > >
> > >It is set in clocksource_enable/disable, even if there is no
> > >enable/disable callback.
> > 
> > Ah, right. But shouldn't we set the flag only if the callback is present and
> > succeed as Boris mentioned it ?
> > 
> 
> What Boris was suggesting was that if the enable exist, set it only if
> it succeed. Which gives something like that:
> 
> int clocksource_enable(struct clocksource *cs)
> {
> 	int ret = 0;
> 
> 	if (cs->enable)
> 		ret = cs->enable(cs);
> 
> 	if (!ret)
> 		cs->flags |= CLOCK_SOURCE_USED;
> 
> 	return 0;

Obviously, that is

return ret;



> }
> 
> I will use that version in v2.
> 
> 
> -- 
> Alexandre Belloni, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: [RFC 1/2] clocksource: track usage

[Kevin Hilman]

Alexandre Belloni <alexandre.belloni@free-electrons.com> writes:

> Track whether the clocksource is enabled or disabled.
>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> ---
>  include/linux/clocksource.h |  4 ++++
>  kernel/time/clocksource.c   | 26 ++++++++++++++++++++++++++
>  kernel/time/timekeeping.c   |  8 +++-----
>  3 files changed, 33 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> index abcafaa20b86..7735902fc5f6 100644
> --- a/include/linux/clocksource.h
> +++ b/include/linux/clocksource.h
> @@ -210,6 +210,8 @@ struct clocksource {
>  #define CLOCK_SOURCE_SUSPEND_NONSTOP		0x80
>  #define CLOCK_SOURCE_RESELECT			0x100
>  
> +#define CLOCK_SOURCE_USED			0x200

minor nit: How about s/USED/ENABLED/ so the flag name is similar to the
function names.

Kevin