Re: [PATCH v2 4/4] serial: Add kserial_rs485 to avoid wasted space due to .padding

[Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>]

On Tue, 30 Aug 2022, Jiri Slaby wrote:

> On 30. 08. 22, 9:29, Ilpo Järvinen wrote:
> > --- a/include/linux/serial_core.h
> > +++ b/include/linux/serial_core.h
> > @@ -31,6 +31,29 @@ struct serial_struct;
> ...
> > + * Must match with struct serial_rs485 in include/uapi/linux/serial.h
> > excluding
> > + * the padding.
> 
> Have you considered BUILD_BUG_ON() checks with few offset_of()s to enforce the
> above?

It's all enforced at the end of serial_core.c already. Would you perhaps 
prefer I'd put them elsewhere or is it fine as is?

/*
 * Compile-time asserts for struct kserial_rs485 and struct serial_rs485 equality
 * (except padding).
 */
static_assert(offsetof(struct kserial_rs485, flags) ==
              offsetof(struct serial_rs485, flags));
static_assert(offsetof(struct kserial_rs485, delay_rts_before_send) ==
              offsetof(struct serial_rs485, delay_rts_before_send));
static_assert(offsetof(struct kserial_rs485, delay_rts_after_send) ==
              offsetof(struct serial_rs485, delay_rts_after_send));
static_assert(offsetof(struct kserial_rs485, addr_recv) ==
              offsetof(struct serial_rs485, addr_recv));
static_assert(offsetof(struct kserial_rs485, addr_dest) ==
              offsetof(struct serial_rs485, addr_dest));
static_assert(sizeof(struct kserial_rs485) <= sizeof(struct serial_rs485));


-- 
 i.

> > +struct kserial_rs485 {
> > +	__u32	flags;
> > +	__u32	delay_rts_before_send;
> > +	__u32	delay_rts_after_send;
> > +	struct {
> > +		__u8    addr_recv;
> > +		__u8    addr_dest;
> > +	};
> > +};