Each fence object holds function pointers of the module that initialized
it. Allowing the module to unload before this fence's release is
catastrophic. So, keep a refcount on the module until the fence is
released.
Signed-off-by: Akhil P Oommen <[email protected]>
---
Changes in v2:
- added description for the new function parameter.
drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
include/linux/dma-fence.h | 10 ++++++++--
2 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 4edb9fd..2aaa44e 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -18,6 +18,7 @@
* more details.
*/
+#include <linux/module.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/atomic.h>
@@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
{
struct dma_fence *fence =
container_of(kref, struct dma_fence, refcount);
+ struct module *module = fence->owner;
trace_dma_fence_destroy(fence);
@@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
fence->ops->release(fence);
else
dma_fence_free(fence);
+
+ module_put(module);
}
EXPORT_SYMBOL(dma_fence_release);
@@ -541,6 +545,7 @@ struct default_wait_cb {
/**
* dma_fence_init - Initialize a custom fence.
+ * @module: [in] the module that calls this API
* @fence: [in] the fence to initialize
* @ops: [in] the dma_fence_ops for operations on this fence
* @lock: [in] the irqsafe spinlock to use for locking this fence
@@ -556,8 +561,9 @@ struct default_wait_cb {
* to check which fence is later by simply using dma_fence_later.
*/
void
-dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
- spinlock_t *lock, u64 context, unsigned seqno)
+_dma_fence_init(struct module *module, struct dma_fence *fence,
+ const struct dma_fence_ops *ops, spinlock_t *lock,
+ u64 context, unsigned seqno)
{
BUG_ON(!lock);
BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
@@ -571,7 +577,11 @@ struct default_wait_cb {
fence->seqno = seqno;
fence->flags = 0UL;
fence->error = 0;
+ fence->owner = module;
+
+ if (!try_module_get(module))
+ fence->owner = NULL;
trace_dma_fence_init(fence);
}
-EXPORT_SYMBOL(dma_fence_init);
+EXPORT_SYMBOL(_dma_fence_init);
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index eb9b05a..8159125 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -36,6 +36,8 @@
/**
* struct dma_fence - software synchronization primitive
+ * @owner: the module that contains fence_ops functions.
+ * Usually THIS_MODULE.
* @refcount: refcount for this fence
* @ops: dma_fence_ops associated with this fence
* @rcu: used for releasing fence with kfree_rcu
@@ -71,6 +73,7 @@
* been completed, or never called at all.
*/
struct dma_fence {
+ struct module *owner;
struct kref refcount;
const struct dma_fence_ops *ops;
struct rcu_head rcu;
@@ -249,8 +252,11 @@ struct dma_fence_ops {
char *str, int size);
};
-void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
- spinlock_t *lock, u64 context, unsigned seqno);
+#define dma_fence_init(fence, ops, lock, context, seqno) _dma_fence_init( \
+ THIS_MODULE, fence, ops, lock, context, seqno)
+void _dma_fence_init(struct module *module, struct dma_fence *fence,
+ const struct dma_fence_ops *ops, spinlock_t *lock, u64 context,
+ unsigned seqno);
void dma_fence_release(struct kref *kref);
void dma_fence_free(struct dma_fence *fence);
--
1.9.1
Hi Akhil,
On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
> Each fence object holds function pointers of the module that
> initialized
> it. Allowing the module to unload before this fence's release is
> catastrophic. So, keep a refcount on the module until the fence is
> released.
>
> Signed-off-by: Akhil P Oommen <[email protected]>
> ---
> Changes in v2:
> - added description for the new function parameter.
>
> drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
> include/linux/dma-fence.h | 10 ++++++++--
> 2 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-
> fence.c
> index 4edb9fd..2aaa44e 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -18,6 +18,7 @@
> * more details.
> */
>
> +#include <linux/module.h>
> #include <linux/slab.h>
> #include <linux/export.h>
> #include <linux/atomic.h>
> @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
> {
> struct dma_fence *fence =
> container_of(kref, struct dma_fence, refcount);
> + struct module *module = fence->owner;
>
> trace_dma_fence_destroy(fence);
>
> @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
> fence->ops->release(fence);
> else
> dma_fence_free(fence);
> +
> + module_put(module);
> }
> EXPORT_SYMBOL(dma_fence_release);
>
> @@ -541,6 +545,7 @@ struct default_wait_cb {
>
> /**
> * dma_fence_init - Initialize a custom fence.
> + * @module: [in] the module that calls this API
> * @fence: [in] the fence to initialize
> * @ops: [in] the dma_fence_ops for operations on this
> fence
> * @lock: [in] the irqsafe spinlock to use for locking
> this fence
> @@ -556,8 +561,9 @@ struct default_wait_cb {
> * to check which fence is later by simply using dma_fence_later.
> */
> void
> -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops
> *ops,
> - spinlock_t *lock, u64 context, unsigned seqno)
> +_dma_fence_init(struct module *module, struct dma_fence *fence,
> + const struct dma_fence_ops *ops, spinlock_t *lock,
> + u64 context, unsigned seqno)
> {
> BUG_ON(!lock);
> BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
> @@ -571,7 +577,11 @@ struct default_wait_cb {
> fence->seqno = seqno;
> fence->flags = 0UL;
> fence->error = 0;
> + fence->owner = module;
> +
> + if (!try_module_get(module))
> + fence->owner = NULL;
>
> trace_dma_fence_init(fence);
> }
> -EXPORT_SYMBOL(dma_fence_init);
> +EXPORT_SYMBOL(_dma_fence_init);
Do we still need to export the symbol, it won't be called from outside
anymore? Other than that looks good to me:
Reviewed-by: Gustavo Padovan <[email protected]>
Gustavo
Quoting Gustavo Padovan (2018-06-22 11:04:16)
> Hi Akhil,
>
> On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
> > Each fence object holds function pointers of the module that
> > initialized
> > it. Allowing the module to unload before this fence's release is
> > catastrophic. So, keep a refcount on the module until the fence is
> > released.
> >
> > Signed-off-by: Akhil P Oommen <[email protected]>
> > ---
> > Changes in v2:
> > - added description for the new function parameter.
> >
> > drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
> > include/linux/dma-fence.h | 10 ++++++++--
> > 2 files changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-
> > fence.c
> > index 4edb9fd..2aaa44e 100644
> > --- a/drivers/dma-buf/dma-fence.c
> > +++ b/drivers/dma-buf/dma-fence.c
> > @@ -18,6 +18,7 @@
> > * more details.
> > */
> >
> > +#include <linux/module.h>
> > #include <linux/slab.h>
> > #include <linux/export.h>
> > #include <linux/atomic.h>
> > @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
> > {
> > struct dma_fence *fence =
> > container_of(kref, struct dma_fence, refcount);
> > + struct module *module = fence->owner;
> >
> > trace_dma_fence_destroy(fence);
> >
> > @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
> > fence->ops->release(fence);
> > else
> > dma_fence_free(fence);
> > +
> > + module_put(module);
> > }
> > EXPORT_SYMBOL(dma_fence_release);
> >
> > @@ -541,6 +545,7 @@ struct default_wait_cb {
> >
> > /**
> > * dma_fence_init - Initialize a custom fence.
> > + * @module: [in] the module that calls this API
> > * @fence: [in] the fence to initialize
> > * @ops: [in] the dma_fence_ops for operations on this
> > fence
> > * @lock: [in] the irqsafe spinlock to use for locking
> > this fence
> > @@ -556,8 +561,9 @@ struct default_wait_cb {
> > * to check which fence is later by simply using dma_fence_later.
> > */
> > void
> > -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops
> > *ops,
> > - spinlock_t *lock, u64 context, unsigned seqno)
> > +_dma_fence_init(struct module *module, struct dma_fence *fence,
> > + const struct dma_fence_ops *ops, spinlock_t *lock,
> > + u64 context, unsigned seqno)
> > {
> > BUG_ON(!lock);
> > BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
> > @@ -571,7 +577,11 @@ struct default_wait_cb {
> > fence->seqno = seqno;
> > fence->flags = 0UL;
> > fence->error = 0;
> > + fence->owner = module;
> > +
> > + if (!try_module_get(module))
> > + fence->owner = NULL;
> >
> > trace_dma_fence_init(fence);
> > }
> > -EXPORT_SYMBOL(dma_fence_init);
> > +EXPORT_SYMBOL(_dma_fence_init);
>
> Do we still need to export the symbol, it won't be called from outside
> anymore? Other than that looks good to me:
There's a big drawback in that a module reference is often insufficient,
and that a reference on the driver (or whatever is required for the
lifetime of the fence) will already hold the module reference.
Considering that we want a few 100k fences in flight per second, is
there no other way to only export a fence with a module reference?
-Chris
On 6/22/2018 3:38 PM, Chris Wilson wrote:
> Quoting Gustavo Padovan (2018-06-22 11:04:16)
>> Hi Akhil,
>>
>> On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
>>> Each fence object holds function pointers of the module that
>>> initialized
>>> it. Allowing the module to unload before this fence's release is
>>> catastrophic. So, keep a refcount on the module until the fence is
>>> released.
>>>
>>> Signed-off-by: Akhil P Oommen <[email protected]>
>>> ---
>>> Changes in v2:
>>> - added description for the new function parameter.
>>>
>>> drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
>>> include/linux/dma-fence.h | 10 ++++++++--
>>> 2 files changed, 21 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-
>>> fence.c
>>> index 4edb9fd..2aaa44e 100644
>>> --- a/drivers/dma-buf/dma-fence.c
>>> +++ b/drivers/dma-buf/dma-fence.c
>>> @@ -18,6 +18,7 @@
>>> * more details.
>>> */
>>>
>>> +#include <linux/module.h>
>>> #include <linux/slab.h>
>>> #include <linux/export.h>
>>> #include <linux/atomic.h>
>>> @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
>>> {
>>> struct dma_fence *fence =
>>> container_of(kref, struct dma_fence, refcount);
>>> + struct module *module = fence->owner;
>>>
>>> trace_dma_fence_destroy(fence);
>>>
>>> @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
>>> fence->ops->release(fence);
>>> else
>>> dma_fence_free(fence);
>>> +
>>> + module_put(module);
>>> }
>>> EXPORT_SYMBOL(dma_fence_release);
>>>
>>> @@ -541,6 +545,7 @@ struct default_wait_cb {
>>>
>>> /**
>>> * dma_fence_init - Initialize a custom fence.
>>> + * @module: [in] the module that calls this API
>>> * @fence: [in] the fence to initialize
>>> * @ops: [in] the dma_fence_ops for operations on this
>>> fence
>>> * @lock: [in] the irqsafe spinlock to use for locking
>>> this fence
>>> @@ -556,8 +561,9 @@ struct default_wait_cb {
>>> * to check which fence is later by simply using dma_fence_later.
>>> */
>>> void
>>> -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops
>>> *ops,
>>> - spinlock_t *lock, u64 context, unsigned seqno)
>>> +_dma_fence_init(struct module *module, struct dma_fence *fence,
>>> + const struct dma_fence_ops *ops, spinlock_t *lock,
>>> + u64 context, unsigned seqno)
>>> {
>>> BUG_ON(!lock);
>>> BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
>>> @@ -571,7 +577,11 @@ struct default_wait_cb {
>>> fence->seqno = seqno;
>>> fence->flags = 0UL;
>>> fence->error = 0;
>>> + fence->owner = module;
>>> +
>>> + if (!try_module_get(module))
>>> + fence->owner = NULL;
>>>
>>> trace_dma_fence_init(fence);
>>> }
>>> -EXPORT_SYMBOL(dma_fence_init);
>>> +EXPORT_SYMBOL(_dma_fence_init);
>> Do we still need to export the symbol, it won't be called from outside
>> anymore? Other than that looks good to me:
Yes. Because dma_fence_init() is now a macro that resolves to
_dma_fence_init().
> There's a big drawback in that a module reference is often insufficient,
> and that a reference on the driver (or whatever is required for the
> lifetime of the fence) will already hold the module reference.
I didn't quite understand what you meant here. Could you please elaborate?
>
> Considering that we want a few 100k fences in flight per second, is
> there no other way to only export a fence with a module reference?
> -Chris
Thanks,
Akhil.
On Fri, Jun 22, 2018 at 11:08:48AM +0100, Chris Wilson wrote:
> Quoting Gustavo Padovan (2018-06-22 11:04:16)
> > Hi Akhil,
> >
> > On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
> > > Each fence object holds function pointers of the module that
> > > initialized
> > > it. Allowing the module to unload before this fence's release is
> > > catastrophic. So, keep a refcount on the module until the fence is
> > > released.
> > >
> > > Signed-off-by: Akhil P Oommen <[email protected]>
> > > ---
> > > Changes in v2:
> > > - added description for the new function parameter.
> > >
> > > drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
> > > include/linux/dma-fence.h | 10 ++++++++--
> > > 2 files changed, 21 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-
> > > fence.c
> > > index 4edb9fd..2aaa44e 100644
> > > --- a/drivers/dma-buf/dma-fence.c
> > > +++ b/drivers/dma-buf/dma-fence.c
> > > @@ -18,6 +18,7 @@
> > > * more details.
> > > */
> > >
> > > +#include <linux/module.h>
> > > #include <linux/slab.h>
> > > #include <linux/export.h>
> > > #include <linux/atomic.h>
> > > @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
> > > {
> > > struct dma_fence *fence =
> > > container_of(kref, struct dma_fence, refcount);
> > > + struct module *module = fence->owner;
> > >
> > > trace_dma_fence_destroy(fence);
> > >
> > > @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
> > > fence->ops->release(fence);
> > > else
> > > dma_fence_free(fence);
> > > +
> > > + module_put(module);
> > > }
> > > EXPORT_SYMBOL(dma_fence_release);
> > >
> > > @@ -541,6 +545,7 @@ struct default_wait_cb {
> > >
> > > /**
> > > * dma_fence_init - Initialize a custom fence.
> > > + * @module: [in] the module that calls this API
> > > * @fence: [in] the fence to initialize
> > > * @ops: [in] the dma_fence_ops for operations on this
> > > fence
> > > * @lock: [in] the irqsafe spinlock to use for locking
> > > this fence
> > > @@ -556,8 +561,9 @@ struct default_wait_cb {
> > > * to check which fence is later by simply using dma_fence_later.
> > > */
> > > void
> > > -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops
> > > *ops,
> > > - spinlock_t *lock, u64 context, unsigned seqno)
> > > +_dma_fence_init(struct module *module, struct dma_fence *fence,
> > > + const struct dma_fence_ops *ops, spinlock_t *lock,
> > > + u64 context, unsigned seqno)
> > > {
> > > BUG_ON(!lock);
> > > BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
> > > @@ -571,7 +577,11 @@ struct default_wait_cb {
> > > fence->seqno = seqno;
> > > fence->flags = 0UL;
> > > fence->error = 0;
> > > + fence->owner = module;
> > > +
> > > + if (!try_module_get(module))
> > > + fence->owner = NULL;
> > >
> > > trace_dma_fence_init(fence);
> > > }
> > > -EXPORT_SYMBOL(dma_fence_init);
> > > +EXPORT_SYMBOL(_dma_fence_init);
> >
> > Do we still need to export the symbol, it won't be called from outside
> > anymore? Other than that looks good to me:
>
> There's a big drawback in that a module reference is often insufficient,
> and that a reference on the driver (or whatever is required for the
> lifetime of the fence) will already hold the module reference.
>
> Considering that we want a few 100k fences in flight per second, is
> there no other way to only export a fence with a module reference?
We'd need to make the timeline a full-blown object (Maarten owes me one
for that design screw-up), and then we could stuff all these things in
there.
And I think that's the right fix, since try_module_get for every
dma_fence_init just ain't cool really :-)
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Mon, Jun 25, 2018 at 09:21:15PM +0530, Akhil P Oommen wrote:
>
>
> On 6/25/2018 1:20 PM, Daniel Vetter wrote:
> > On Fri, Jun 22, 2018 at 11:08:48AM +0100, Chris Wilson wrote:
> > > Quoting Gustavo Padovan (2018-06-22 11:04:16)
> > > > Hi Akhil,
> > > >
> > > > On Fri, 2018-06-22 at 15:10 +0530, Akhil P Oommen wrote:
> > > > > Each fence object holds function pointers of the module that
> > > > > initialized
> > > > > it. Allowing the module to unload before this fence's release is
> > > > > catastrophic. So, keep a refcount on the module until the fence is
> > > > > released.
> > > > >
> > > > > Signed-off-by: Akhil P Oommen <[email protected]>
> > > > > ---
> > > > > Changes in v2:
> > > > > - added description for the new function parameter.
> > > > >
> > > > > drivers/dma-buf/dma-fence.c | 16 +++++++++++++---
> > > > > include/linux/dma-fence.h | 10 ++++++++--
> > > > > 2 files changed, 21 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-
> > > > > fence.c
> > > > > index 4edb9fd..2aaa44e 100644
> > > > > --- a/drivers/dma-buf/dma-fence.c
> > > > > +++ b/drivers/dma-buf/dma-fence.c
> > > > > @@ -18,6 +18,7 @@
> > > > > * more details.
> > > > > */
> > > > > +#include <linux/module.h>
> > > > > #include <linux/slab.h>
> > > > > #include <linux/export.h>
> > > > > #include <linux/atomic.h>
> > > > > @@ -168,6 +169,7 @@ void dma_fence_release(struct kref *kref)
> > > > > {
> > > > > struct dma_fence *fence =
> > > > > container_of(kref, struct dma_fence, refcount);
> > > > > + struct module *module = fence->owner;
> > > > > trace_dma_fence_destroy(fence);
> > > > > @@ -178,6 +180,8 @@ void dma_fence_release(struct kref *kref)
> > > > > fence->ops->release(fence);
> > > > > else
> > > > > dma_fence_free(fence);
> > > > > +
> > > > > + module_put(module);
> > > > > }
> > > > > EXPORT_SYMBOL(dma_fence_release);
> > > > > @@ -541,6 +545,7 @@ struct default_wait_cb {
> > > > > /**
> > > > > * dma_fence_init - Initialize a custom fence.
> > > > > + * @module: [in] the module that calls this API
> > > > > * @fence: [in] the fence to initialize
> > > > > * @ops: [in] the dma_fence_ops for operations on this
> > > > > fence
> > > > > * @lock: [in] the irqsafe spinlock to use for locking
> > > > > this fence
> > > > > @@ -556,8 +561,9 @@ struct default_wait_cb {
> > > > > * to check which fence is later by simply using dma_fence_later.
> > > > > */
> > > > > void
> > > > > -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops
> > > > > *ops,
> > > > > - spinlock_t *lock, u64 context, unsigned seqno)
> > > > > +_dma_fence_init(struct module *module, struct dma_fence *fence,
> > > > > + const struct dma_fence_ops *ops, spinlock_t *lock,
> > > > > + u64 context, unsigned seqno)
> > > > > {
> > > > > BUG_ON(!lock);
> > > > > BUG_ON(!ops || !ops->wait || !ops->enable_signaling ||
> > > > > @@ -571,7 +577,11 @@ struct default_wait_cb {
> > > > > fence->seqno = seqno;
> > > > > fence->flags = 0UL;
> > > > > fence->error = 0;
> > > > > + fence->owner = module;
> > > > > +
> > > > > + if (!try_module_get(module))
> > > > > + fence->owner = NULL;
> > > > > trace_dma_fence_init(fence);
> > > > > }
> > > > > -EXPORT_SYMBOL(dma_fence_init);
> > > > > +EXPORT_SYMBOL(_dma_fence_init);
> > > > Do we still need to export the symbol, it won't be called from outside
> > > > anymore? Other than that looks good to me:
> > > There's a big drawback in that a module reference is often insufficient,
> > > and that a reference on the driver (or whatever is required for the
> > > lifetime of the fence) will already hold the module reference.
> > >
> > > Considering that we want a few 100k fences in flight per second, is
> > > there no other way to only export a fence with a module reference?
> > We'd need to make the timeline a full-blown object (Maarten owes me one
> > for that design screw-up), and then we could stuff all these things in
> > there.
> >
> > And I think that's the right fix, since try_module_get for every
> > dma_fence_init just ain't cool really :-)
> > -Daniel
> Thanks for the feedback, Daniel.
> I see your point, but I am not sure how much impact an extra refcounting
> would create considering the whole effort of setting up a new fence. Also,
> this refcounting is not required for built-in modules.
>
> As of now, unloading a kernel module that uses fence_init() is an easy way
> to bring down the system. This patch simply fixes that. What you have
> suggested sounds like a non-trivial effort which someone who is more
> familiar with this code base can do a better job than me. Perhaps we can
> take this patch now to fix the issue at hand and later somebody else can
> share a more optimal solution. :)
Module unload is a developer-only feature for a reason. Given that I don't
think fixing this with a hack is the right approach. And dma_fence_init()
is supposed to be really fast.
Also note that you can fix this already for your own driver by simply
waiting for all pending dma_fences to get released, so I don't think it's
super-important to land this asap.
Yes the real fix is a bit more involved, but shouldn't be too hard to pull
off really.
-Daniel
>
> @Gustavo & @Sumit, I would like the maintainers to take a decision here.
>
> -Akhil.
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch