Re: [Xen-devel] [PATCH 10/20] libxl: Make libxl__zalloc et al tolerate a NULL gc

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-03-16 at 16:26 +0000, Ian Jackson wrote:
> Arrange that if we pass NULL as a gc, we simply don't register the
> pointer.  This instantly gives us non-gc'ing but error-checking
> versions of malloc, realloc, vasprintf, etc.
> 
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

We could consider __attribute__((nonnull)) for the other helper
functions in that section of libxl_internal.h.

> ---
>  tools/libxl/libxl_internal.c |    5 ++++-
>  tools/libxl/libxl_internal.h |   21 +++++++++++++--------
>  2 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
> index dfa2153..de7c3a8 100644
> --- a/tools/libxl/libxl_internal.c
> +++ b/tools/libxl/libxl_internal.c
> @@ -29,6 +29,9 @@ void libxl__ptr_add(libxl__gc *gc, void *ptr)
>  {
>      int i;
>  
> +    if (!gc)
> +        return;
> +
>      if (!ptr)
>          return;
>  
> @@ -96,7 +99,7 @@ void *libxl__realloc(libxl__gc *gc, void *ptr, size_t 
> new_size)
>  
>      if (ptr == NULL) {
>          libxl__ptr_add(gc, new_ptr);
> -    } else if (new_ptr != ptr) {
> +    } else if (new_ptr != ptr && gc != NULL) {
>          for (i = 0; i < gc->alloc_maxsize; i++) {
>              if (gc->alloc_ptrs[i] == ptr) {
>                  gc->alloc_ptrs[i] = new_ptr;
> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> index e59a19b..86f25be 100644
> --- a/tools/libxl/libxl_internal.h
> +++ b/tools/libxl/libxl_internal.h
> @@ -381,30 +381,35 @@ static inline libxl_ctx *libxl__gc_owner(libxl__gc *gc)
>   *
>   * All pointers returned by these functions are registered for garbage
>   * collection on exit from the outermost libxl callframe.
> + *
> + * However, where the argument is stated to be "gc_opt", NULL may be
> + * passed instead, in which case no garbage collection will occur; the
> + * pointer must later be freed with free().  This is for memory
> + * allocations of types (b) and (c).
>   */
>  /* register @ptr in @gc for free on exit from outermost libxl callframe. */
> -_hidden void libxl__ptr_add(libxl__gc *gc, void *ptr);
> +_hidden void libxl__ptr_add(libxl__gc *gc_opt, void *ptr);
>  /* if this is the outermost libxl callframe then free all pointers in @gc */
>  _hidden void libxl__free_all(libxl__gc *gc);
>  /* allocate and zero @bytes. (similar to a gc'd malloc(3)+memzero()) */
> -_hidden void *libxl__zalloc(libxl__gc *gc, int bytes);
> +_hidden void *libxl__zalloc(libxl__gc *gc_opt, int bytes);
>  /* allocate and zero memory for an array of @nmemb members of @size each.
>   * (similar to a gc'd calloc(3)). */
> -_hidden void *libxl__calloc(libxl__gc *gc, size_t nmemb, size_t size);
> +_hidden void *libxl__calloc(libxl__gc *gc_opt, size_t nmemb, size_t size);
>  /* change the size of the memory block pointed to by @ptr to @new_size bytes.
>   * unlike other allocation functions here any additional space between the
>   * oldsize and @new_size is not initialised (similar to a gc'd realloc(3)). 
> */
> -_hidden void *libxl__realloc(libxl__gc *gc, void *ptr, size_t new_size);
> +_hidden void *libxl__realloc(libxl__gc *gc_opt, void *ptr, size_t new_size);
>  /* print @fmt into an allocated string large enoughto contain the result.
>   * (similar to gc'd asprintf(3)). */
> -_hidden char *libxl__sprintf(libxl__gc *gc, const char *fmt, ...) 
> PRINTF_ATTRIBUTE(2, 3);
> +_hidden char *libxl__sprintf(libxl__gc *gc_opt, const char *fmt, ...) 
> PRINTF_ATTRIBUTE(2, 3);
>  /* duplicate the string @c (similar to a gc'd strdup(3)). */
> -_hidden char *libxl__strdup(libxl__gc *gc, const char *c);
> +_hidden char *libxl__strdup(libxl__gc *gc_opt, const char *c);
>  /* duplicate at most @n bytes of string @c (similar to a gc'd strndup(3)). */
> -_hidden char *libxl__strndup(libxl__gc *gc, const char *c, size_t n);
> +_hidden char *libxl__strndup(libxl__gc *gc_opt, const char *c, size_t n);
>  /* strip the last path component from @s and return as a newly allocated
>   * string. (similar to a gc'd dirname(3)). */
> -_hidden char *libxl__dirname(libxl__gc *gc, const char *s);
> +_hidden char *libxl__dirname(libxl__gc *gc_opt, const char *s);
>  
>  _hidden char **libxl__xs_kvs_of_flexarray(libxl__gc *gc, flexarray_t *array, 
> int length);
>  



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