On Fri, 15 Dec 2000, J . A . Magallon wrote:
>
> On 2000/12/15 Werner Almesberger wrote:
> > LA Walsh wrote:
> >
> > Exception: opaque types; there one would have to go via a __ identifier,
> > i.e.
> >
> > <public>/foo.h defines struct __foo ...;
> > <public>/bar.h includes <public>/foo.h
> > and uses #define FOOSIZE sizeof(struct __foo)
> > <private>/foo.h either typedef struct __foo foo_t;
> > or #define foo __foo /* ugly */
> >
>
> Easier: public kernel interfaces only work through pointers.
> <public>/foo.h typedef struct foo foo_t;
> foo_t* foo_new();
> <private>/foo.h includes <public>/foo.h
> struct foo { ............... };
> and uses #define FOOSIZE sizeof(foo_t)
>
> Drawback: public access is slow (always through foo_set_xxxx_field(foo_t*))
> private access from kernel or modules is fast (foo_t->x = ...)
> Advantage: kernel can change, foo_t internals can change and it is binary
> compatible. Even public headers can be kernel version
> independent.
I think collectively we're mixing what should really be two seperate but
related issues: userland interface from /usr/include/linux; and exported
kernel header interface for third-party modules.
>From a first reading, your Drawback: appears to belong to the sphere of
kernel interface, and your Advantage: to the sphere of userland interface.
But on the second reading (after opening a bottle of Jones) I can see how
the Advantage: would apply to both spheres.
I'm just asking that people please try to be a little more precise with
the rather imprecise list language.
--Ferret
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