Described restrictions for common HAL object methods.
Inheritance of HAL object is performed by composing a child structure of a
single parent structure located at offset 0 followed by new data members
and function pointers in the child structure.
For example,
struct child {
struct parent common;
int a_data_member;
void (*a_method)(struct child *c, int v);
};
HAL code assumes this layout when accessing child structures given a pointer
to a parent structure such that users write code like the following...
void child_method(struct *parent, int v) {
struct child * c = (struct child*)parent;
// do stuff with c
}
Code above will break if a member is added before "common" in "struct child".
This change adds comments that describe the restriction on the location of
parent HAL objects within a derived HAL object. HAL objects that already
have comments that describe the required location of parent objects are not
modified.
Change-Id: Ibe4300275286ef275b2097534c84f1029d761d87
diff --git a/include/hardware/activity_recognition.h b/include/hardware/activity_recognition.h
index 3d3c1bd..ecac856 100644
--- a/include/hardware/activity_recognition.h
+++ b/include/hardware/activity_recognition.h
@@ -103,6 +103,12 @@
} activity_event_t;
typedef struct activity_recognition_module {
+ /**
+ * Common methods of the activity recognition module. This *must* be the first member of
+ * activity_recognition_module as users of this structure will cast a hw_module_t to
+ * activity_recognition_module pointer in contexts where it's known the hw_module_t
+ * references an activity_recognition_module.
+ */
hw_module_t common;
/*
@@ -126,6 +132,12 @@
} activity_recognition_callback_procs_t;
typedef struct activity_recognition_device {
+ /**
+ * Common methods of the activity recognition device. This *must* be the first member of
+ * activity_recognition_device as users of this structure will cast a hw_device_t to
+ * activity_recognition_device pointer in contexts where it's known the hw_device_t
+ * references an activity_recognition_device.
+ */
hw_device_t common;
/*