[FFmpeg-devel] [PATCH 05/29] lavu/opt: distinguish between native and foreign access for AVOption fields

[Anton Khirnov <anton@khirnov.net>]

Native access is from the code that declared the options, foreign access
is from code that is using the options. Forbid foreign access to
AVOption.offset/default_val, for which there is no good reason, and
which should allow us more freedom in extending their semantics in a
compatible way.
---
 libavutil/opt.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libavutil/opt.h b/libavutil/opt.h
index e34b8506f8..e402f6a0a0 100644
--- a/libavutil/opt.h
+++ b/libavutil/opt.h
@@ -43,6 +43,16 @@
  * ("objects"). An option can have a help text, a type and a range of possible
  * values. Options may then be enumerated, read and written to.
  *
+ * There are two modes of access to members of AVOption and its child structs.
+ * One is called 'native access', and refers to access from the code that
+ * declares the AVOption in question.  The other is 'foreign access', and refers
+ * to access from other code.
+ *
+ * Certain struct members in this header are documented as 'native access only'
+ * or similar - it means that only the code that declared the AVOption in
+ * question is allowed to access the field. This allows us to extend the
+ * semantics of those fields without breaking API compatibility.
+ *
  * @section avoptions_implement Implementing AVOptions
  * This section describes how to add AVOptions capabilities to a struct.
  *
@@ -301,6 +311,8 @@ typedef struct AVOption {
     const char *help;
 
     /**
+     * Native access only.
+     *
      * The offset relative to the context structure where the option
      * value is stored. It should be 0 for named constants.
      */
@@ -308,6 +320,8 @@ typedef struct AVOption {
     enum AVOptionType type;
 
     /**
+     * Native access only.
+     *
      * the default value for scalar options
      */
     union {
-- 
2.43.0

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