Re: [PATCH v3 14/25] tools/xenstore: change talloc_free() to take a const pointer

[Julien Grall <julien@xxxxxxx>]

Hi Juergen,

On 24/07/2023 12:02, Juergen Gross wrote:
> With talloc_free() and related functions not taking a ponter to const
typo: s/ponter/pointer/

> it is tedious to use the const attribute for talloc()-ed memory in
> many cases.
>
> Change the related prototypes to use "const void *" instead of
> "void *".
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V3:
> - new patch
> ---
>   tools/xenstore/talloc.c | 8 ++++----
>   tools/xenstore/talloc.h | 4 ++--
>   2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/tools/xenstore/talloc.c b/tools/xenstore/talloc.c
> index 23c3a23b19..4f08dbec59 100644
> --- a/tools/xenstore/talloc.c
> +++ b/tools/xenstore/talloc.c
> @@ -319,7 +319,7 @@ static int talloc_unreference(const void *context, const 
> void *ptr)
>     remove a specific parent context from a pointer. This is a more
>     controlled varient of talloc_free()
>   */
> -int talloc_unlink(const void *context, void *ptr)
> +int talloc_unlink(const void *context, const void *ptr)
>   {
>         struct talloc_chunk *tc_p, *new_p;
>         void *new_parent;
> @@ -499,7 +499,7 @@ void *talloc_init(const char *fmt, ...)
>     should probably not be used in new code. It's in here to keep the talloc
>     code consistent across Samba 3 and 4.
>   */
> -static void talloc_free_children(void *ptr)
> +static void talloc_free_children(const void *ptr)
>   {
>         struct talloc_chunk *tc;
>   
> @@ -539,7 +539,7 @@ static void talloc_free_children(void *ptr)
>      will not be freed if the ref_count is > 1 or the destructor (if
>      any) returns non-zero
>   */
> -int talloc_free(void *ptr)
> +int talloc_free(const void *ptr)
>   {
>         int saved_errno = errno;
>         struct talloc_chunk *tc;
> @@ -571,7 +571,7 @@ int talloc_free(void *ptr)
>                         goto err;
>                 }
>                 tc->destructor = (talloc_destructor_t)-1;
> -               if (d(ptr) == -1) {
> +               if (d((void *)ptr) == -1) {
AFAICT, you can't propagate the const because the destructor may need to 
modify the content. I guess this is a necessary evil here but it would 
be good to document it.
Cheers,

--
Julien Grall