On Friday 17 July 2015 14:59:48 Arnd Bergmann wrote:
> Also, __kernel_timespec is defined to be always 64-bit wide. This means
> if we do this change (assuming we drop the #define above), then user space
> will always see the new definition of this structure, and programs
> compiled against the latest header will no longer work on older kernels.
>
> Is this what you had in mind?
>
> We could decide to do it like this, and we have historically done changes
> to the ioctl interface this way, but I'm not sure if we want to do it
> for all ioctls.
>
> The alternative is to leave the 'timespec' visible here for user space,
> so user programs will see either the old or the new definition of struct
> depending on their timespec definition, and only programs built with
> 64-bit time_t will require new kernels.
For clarification: The approach of changing the existing data structure
definition will work in this particular case, but a lot of other
ioctl commands just pass a plain time_t / timespec / timeval.
For those commands, we absolutely have to make sure that kernel and
user space agree on the command code for old and new argument format,
and that will involve an #ifdef like the example I gave. Aside from
ioctl, we need the same thing for a couple of other interfaces like
setsockopts.
Arnd
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