Re: [RFD] posix-timers: CRIU woes

[Cyrill Gorcunov]

On Wed, May 10, 2023 at 01:16:26AM -0700, Andrey Vagin wrote:
... 
> Hi Thomas,
> 
> If you give us a new API to create timers with specified id-s, we will
> figure out how to live with it. It isn't good to ask users to update
> CRIU to work on new kernels, but here are reasons and event improvements
> for CRIU, so I think it's worth it.
> 
> As for API, we can use one bit of sigevent.sigev_notify to request a
> timer with a specified id.

Which will do the trick but would look somehow strange I think, since signals
are not some how related to timer's ID. Another option might be to use output
`created_timer_id` parameter as an input cookie.

Say we describe input as

struct {
	u32 magic;
	timer_t timer_id;
};

Then if magic doesn't match we use `created_timer_id` for output only, and
otherwise we read `timer_id` from input and use it. Of course there is a
chance that some unitialized memory passed with existing old programs but
i think false positive gonna be very-very low if ever. Just IMHO.

	Cyrill