[2/8] of: Introduce for_each_*_child_of_node_scoped() to automate of_node_put() handling

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>

To avoid issues with out of order cleanup, or ambiguity about when the
auto freed data is first instantiated, do it within the for loop definition.

The disadvantage is that the struct device_node *child variable creation
is not immediately obvious where this is used.
However, in many cases, if there is another definition of
struct device_node *child; the compiler / static analysers will notify us
that it is unused, or uninitialized.

Note that, in the vast majority of cases, the _available_ form should be
used and as code is converted to these scoped handers, we should confirm
that any cases that do not check for available have a good reason not
to.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 include/linux/of.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

On Sun, 11 Feb 2024, Jonathan Cameron wrote:

> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> To avoid issues with out of order cleanup, or ambiguity about when the
> auto freed data is first instantiated, do it within the for loop definition.
>
> The disadvantage is that the struct device_node *child variable creation
> is not immediately obvious where this is used.
> However, in many cases, if there is another definition of
> struct device_node *child; the compiler / static analysers will notify us
> that it is unused, or uninitialized.
>
> Note that, in the vast majority of cases, the _available_ form should be
> used and as code is converted to these scoped handers, we should confirm
> that any cases that do not check for available have a good reason not
> to.

Is it a good idea to make the two changes at once?  Maybe it would slow
down the use of the scoped form, which can really simplify the code.

julia

>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  include/linux/of.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 50e882ee91da..024dda54b9c7 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -1430,10 +1430,23 @@ static inline int of_property_read_s32(const struct device_node *np,
>  #define for_each_child_of_node(parent, child) \
>  	for (child = of_get_next_child(parent, NULL); child != NULL; \
>  	     child = of_get_next_child(parent, child))
> +
> +#define for_each_child_of_node_scoped(parent, child) \
> +	for (struct device_node *child __free(device_node) =		\
> +	     of_get_next_child(parent, NULL);				\
> +	     child != NULL;						\
> +	     child = of_get_next_child(parent, child))
> +
>  #define for_each_available_child_of_node(parent, child) \
>  	for (child = of_get_next_available_child(parent, NULL); child != NULL; \
>  	     child = of_get_next_available_child(parent, child))
>
> +#define for_each_available_child_of_node_scoped(parent, child) \
> +	for (struct device_node *child __free(device_node) =		\
> +	     of_get_next_available_child(parent, NULL);			\
> +	     child != NULL;						\
> +	     child = of_get_next_available_child(parent, child))
> +
>  #define for_each_of_cpu_node(cpu) \
>  	for (cpu = of_get_next_cpu_node(NULL); cpu != NULL; \
>  	     cpu = of_get_next_cpu_node(cpu))
> --
> 2.43.1
>
>

On Mon, 12 Feb 2024 09:20:35 +0100 (CET)
Julia Lawall <julia.lawall@inria.fr> wrote:

> On Sun, 11 Feb 2024, Jonathan Cameron wrote:
> 
> > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >
> > To avoid issues with out of order cleanup, or ambiguity about when the
> > auto freed data is first instantiated, do it within the for loop definition.
> >
> > The disadvantage is that the struct device_node *child variable creation
> > is not immediately obvious where this is used.
> > However, in many cases, if there is another definition of
> > struct device_node *child; the compiler / static analysers will notify us
> > that it is unused, or uninitialized.
> >
> > Note that, in the vast majority of cases, the _available_ form should be
> > used and as code is converted to these scoped handers, we should confirm
> > that any cases that do not check for available have a good reason not
> > to.  
> 
> Is it a good idea to make the two changes at once?  Maybe it would slow
> down the use of the scoped form, which can really simplify the code.

Good question.  I combined them based on what I think Rob was asking for.

Rob,

What would you prefer?

Jonathan

> 
> julia
> 
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >  include/linux/of.h | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index 50e882ee91da..024dda54b9c7 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -1430,10 +1430,23 @@ static inline int of_property_read_s32(const struct device_node *np,
> >  #define for_each_child_of_node(parent, child) \
> >  	for (child = of_get_next_child(parent, NULL); child != NULL; \
> >  	     child = of_get_next_child(parent, child))
> > +
> > +#define for_each_child_of_node_scoped(parent, child) \
> > +	for (struct device_node *child __free(device_node) =		\
> > +	     of_get_next_child(parent, NULL);				\
> > +	     child != NULL;						\
> > +	     child = of_get_next_child(parent, child))
> > +
> >  #define for_each_available_child_of_node(parent, child) \
> >  	for (child = of_get_next_available_child(parent, NULL); child != NULL; \
> >  	     child = of_get_next_available_child(parent, child))
> >
> > +#define for_each_available_child_of_node_scoped(parent, child) \
> > +	for (struct device_node *child __free(device_node) =		\
> > +	     of_get_next_available_child(parent, NULL);			\
> > +	     child != NULL;						\
> > +	     child = of_get_next_available_child(parent, child))
> > +
> >  #define for_each_of_cpu_node(cpu) \
> >  	for (cpu = of_get_next_cpu_node(NULL); cpu != NULL; \
> >  	     cpu = of_get_next_cpu_node(cpu))
> > --
> > 2.43.1
> >
> >