[Mesa-dev] [PATCH 05/11] compiler/blob: Add a concept of a fixed-allocation blob

[Jordan Justen]

I think the commit message should include something like:

With a fixed allocation blob, the data buffer is managed by the
caller, and can't be grown by blob writes.

I also think it'd be better to add the NULL fixed allocation blob
support in a separate patch. (It looks like the real motivation is the
ability to determine the blob size using a NULL buffer, so it seems
like that deserves its own patch. :)

-Jordan

On 2017-10-11 13:38:45, Jason Ekstrand wrote:
> ---
>  src/compiler/blob.c | 24 +++++++++++++++++++++---
>  src/compiler/blob.h | 23 ++++++++++++++++++++++-
>  2 files changed, 43 insertions(+), 4 deletions(-)
> 
> diff --git a/src/compiler/blob.c b/src/compiler/blob.c
> index 0b42871..59ad8a3 100644
> --- a/src/compiler/blob.c
> +++ b/src/compiler/blob.c
> @@ -52,6 +52,11 @@ grow_to_fit(struct blob *blob, size_t additional)
>     if (blob->size + additional <= blob->allocated)
>        return true;
>  
> +   if (blob->fixed_allocation) {
> +      blob->out_of_memory = true;
> +      return false;
> +   }
> +
>     if (blob->allocated == 0)
>        to_allocate = BLOB_INITIAL_SIZE;
>     else
> @@ -86,7 +91,8 @@ align_blob(struct blob *blob, size_t alignment)
>        if (!grow_to_fit(blob, new_size - blob->size))
>           return false;
>  
> -      memset(blob->data + blob->size, 0, new_size - blob->size);
> +      if (blob->data)
> +         memset(blob->data + blob->size, 0, new_size - blob->size);
>        blob->size = new_size;
>     }
>  
> @@ -104,6 +110,16 @@ blob_init(struct blob *blob)
>  {
>     blob->data = NULL;
>     blob->allocated = 0;
> +   blob->fixed_allocation = false;
> +   blob->size = 0;
> +}
> +
> +void
> +blob_init_fixed(struct blob *blob, void *data, size_t size)
> +{
> +   blob->data = data;
> +   blob->allocated = size;
> +   blob->fixed_allocation = true;
>     blob->size = 0;
>  }
>  
> @@ -119,7 +135,8 @@ blob_overwrite_bytes(struct blob *blob,
>  
>     VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
>  
> -   memcpy(blob->data + offset, bytes, to_write);
> +   if (blob->data)
> +      memcpy(blob->data + offset, bytes, to_write);
>  
>     return true;
>  }
> @@ -132,7 +149,8 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write)
>  
>     VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
>  
> -   memcpy(blob->data + blob->size, bytes, to_write);
> +   if (blob->data)
> +      memcpy(blob->data + blob->size, bytes, to_write);
>     blob->size += to_write;
>  
>     return true;
> diff --git a/src/compiler/blob.h b/src/compiler/blob.h
> index fd13a16..1ef6d99 100644
> --- a/src/compiler/blob.h
> +++ b/src/compiler/blob.h
> @@ -56,6 +56,12 @@ struct blob {
>     /** The number of bytes that have actual data written to them. */
>     size_t size;
>  
> +   /** True if \c data a fixed allocation that we cannot resize
> +    *
> +    * \see blob_init_fixed
> +    */
> +   bool fixed_allocation;
> +
>     /**
>      * True if we've ever failed to realloc or if we go pas the end of a fixed
>      * allocation blob.
> @@ -85,12 +91,27 @@ void
>  blob_init(struct blob *blob);
>  
>  /**
> + * Init a new, fixed-size blob.
> + *
> + * A fixed-size blob has a fixed block of data that will not be freed on
> + * blob_finish and will never be grown.  If we hit the end, we simply start
> + * returning false from the write functions.
> + *
> + * If a fixed-size blob has a NULL data pointer then the blob no data is
> + * written but it otherwise operates normally.  This can be used to determine
> + * the size that will be required to write a given data structure.
> + */
> +void
> +blob_init_fixed(struct blob *blob, void *data, size_t size);
> +
> +/**
>   * Destroy a blob and free its memory.
>   */
>  static inline void
>  blob_finish(struct blob *blob)
>  {
> -   free(blob->data);
> +   if (!blob->fixed_allocation)
> +      free(blob->data);
>  }
>  
>  /**
> -- 
> 2.5.0.400.gff86faf
> 
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