On 4/15/19 10:22 AM, Adhemerval Zanella wrote:
>>
>> New interfaces are only necessary for the handful of architectures that
>> don't have the speed fields *and* to space to put them in.
>
> Based on your WIP, it seems that both sparc and mips could be adapted.
> Do we still have glibc supported architecture that would require compat
> symbols?
>
>>
>> Using symbol versioning doesn't really help much since the real problem is
>> that struct termios can be passed around in userspace, and the interfaces
>> between user space libraries don't have any versioning. However, my POC code
>> deals with that too by only seeing BOTHER when necessary, so if the
>> structure is extended garbage in the extra fields will be ignored unless new
>> baud rates are in use.
>
> Yeah, we discussed this earlier and if recall correctly it was not settled
> that all architectures would allow the use to extra space for the new
> fields. It seems the case, which makes the adaptation for termios2 even
> easier.
>
> The question I have for kernel side is whether termios2 is fully compatible
> with termios, meaning that if there is conner cases we need to handle in
> userland.
>
It depends on what you mean with "fully compatible."
Functionality-wise, the termios2 interfaces are a strict superset. There
is not, however, any guarantee that struct kernel_termios2 *contains* a
contiguous binary equivalent to struct kernel_termios (in fact, on most
architectures, it doesn't.)
>>
>> My POC code deals with Alpha as well by falling back to the old interfaces
>> if necessary and possible, otherwise return error.
>>
>> Exporting termios2 to user space feels a bit odd at this stage as it would
>> only be usable as a fallback on old glibc. Call it kernel_termios2 at least.
>> ioctls using struct termios *must* be changed to kernel_termios anyway!
>>
>
> I still prefer to avoid export it to userland and make it usable through
> default termios, as your wip does. My understanding is new interfaces
> should be semantic equal to current one with the only deviation that
> non-standard baudrates will handled as its values. The only issue I
> can foresee is if POSIX starts to export new bauds value.
>
... which will be easy to handle: just define a Bxxxx constant with the
value equal to the baud rate.
-hhpa
