[libvirt] [PATCH v3 01/35] util: alloc: add macros for implementing automatic cleanup functionality

[Erik Skultety]

On Sat, Jun 30, 2018 at 02:30:05PM +0530, Sukrit Bhatnagar wrote:
> New macros are introduced which help in adding GNU C's cleanup
> attribute to variable declarations. Variables declared with these
> macros will have their allocated memory freed automatically when
> they go out of scope.
>
> Signed-off-by: Sukrit Bhatnagar <skrtbhtngr at gmail.com>
> ---
>  src/util/viralloc.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>
> diff --git a/src/util/viralloc.h b/src/util/viralloc.h
> index 69d0f90..5c1d0d5 100644
> --- a/src/util/viralloc.h
> +++ b/src/util/viralloc.h
> @@ -596,4 +596,48 @@ void virAllocTestInit(void);
>  int virAllocTestCount(void);
>  void virAllocTestOOM(int n, int m);
>  void virAllocTestHook(void (*func)(int, void*), void *data);
> +
> +# define VIR_AUTOPTR_TYPE_NAME(type) type##AutoPtr
> +# define VIR_AUTOPTR_FUNC_NAME(type) type##AutoPtrFree
> +
> +/**
> + * VIR_DEFINE_AUTOPTR_FUNC:
> + * @type: type of the variable to be freed automatically
> + * @func: cleanup function to be automatically called
> + *
> + * This macro defines a function for automatic freeing of
> + * resources allocated to a variable of type @type. This newly
> + * defined function works as a necessary wrapper around @func.
> + */
> +# define VIR_DEFINE_AUTOPTR_FUNC(type, func) \
> +    typedef type *VIR_AUTOPTR_TYPE_NAME(type); \

So, it's not visible at first glance how ^this typedef is used...

> +    static inline void VIR_AUTOPTR_FUNC_NAME(type)(type **_ptr) \
> +    { \
> +        if (*_ptr) \
> +            (func)(*_ptr); \
> +        *_ptr = NULL; \
> +    } \

...therefore I'd write it explicitly as

VIR_AUTOPTR_FUNC_NAME(type)(VIR_AUTOPTR_TYPE_NAME(type) *_ptr)

> +
> +# define VIR_AUTOPTR(type) \
> +    __attribute__((cleanup(VIR_AUTOPTR_FUNC_NAME(type)))) VIR_AUTOPTR_TYPE_NAME(type)
> +

Also, since we're going to use it like this:
VIR_AUTOPTR(virDomainDef) foo

instead of this:
VIR_AUTOPTR(virDomainDefPtr) foo

why do we need VIR_AUTOPTR_TYPE_NAME anyway, since you could just use
"type *" in the VIR_AUTOPTR macro definition and that should work for external
types as well.

Erik