buflib: Add a define telling the per-alloc overhead.

This allows buflib clients to more accurately estimate the total memory usage.
It's still not 100% accurate because the handle table grows in blocks, thus
buflib might use more memory that caused by allocations directly.

Change-Id: I68338bb94f510ad188fcb588aebf895b5f9197c5

1 files changed, 11 insertions, 0 deletions

diff --git a/firmware/include/buflib.h b/firmware/include/buflib.h
index e912429b1f..1bae3e7a3f 100644
--- a/firmware/include/buflib.h
+++ b/firmware/include/buflib.h
@@ -54,6 +54,17 @@ struct buflib_context
 };
 
 /**
+ * This declares the minimal overhead that is required per alloc. These
+ * are bytes that are allocated from the context's pool in addition
+ * to the actually requested number of bytes.
+ *
+ * The total number of bytes consumed by an allocation is
+ * BUFLIB_ALLOC_OVERHEAD + requested bytes + strlen(<name passed to
+ * buflib_alloc_ex()) + pad to pointer size
+ */
+#define BUFLIB_ALLOC_OVERHEAD (6*sizeof(union buflib_data))
+
+/**
  * Callbacks used by the buflib to inform allocation that compaction
  * is happening (before data is moved)
  *