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
fb and gralloc are part of the same HAL for now,
but for clarity we split them into these two headers.
Change-Id: I8e9e3068e47f0d94dd7c145d72fdc2e9fff24af5
