On 21 Feb 2014 02:17, "Antti Kantee" <[email protected]> wrote:
>
> Hmm,
>
> So we were looking at NetBSD's ping6 for inclusion in rumprun. ping6
> does essentially:
>
> signal(SIGALRM, thehand);
> setitimer(...);
> rv = poll(..., -1);
> if (rv == -1 && errno == EINTR) {
> ...
> }
>
> Now, it's easy enough to get a rump kernel to deliver a host SIGALRM for
> both local and remote clients (in fact, it happens already -- at least
> on POSIX hosts).
>
> However, that does not take care of interrupting the rump kernel syscall
> to return EINTR. That said, rump kernels already support interrupting
> syscall sleeps because that was required for correct thread+exec
> semantics. Even though signals could more or less use the same facility
> as exec, there's another problem: to properly decide whether the syscall
> can be interrupted, we'd need to track, among other things, the signal
> mask. Doing signals properly would mean adding sigprocmask() and that
> family of calls. Maintaining two signal masks (rump kernel and host)
> might get quite confusing quickly. Confusion would only be compounded
> by the fact that not all hosts even have signals.
>
> The options I can see are:
> 1) make signals completely mimic POSIX (and fix bugs forever)
> 2) leave things as they currently are (rump kernels make a reasonable
> effort to cater to signal-happy programs, though semantics are so-so)
> 3) completely rip out any host signal delivery (equally good/bad for all
> hosts, and does not give a false sense of "1")
>
> I'm inclined to do "2" (because that's the least amount of work ;). The
> creative way NetBSD's ping6 avoids the timeout argument to poll() would
> have to be changed, and while changing an existing, real-world program
> pains me a bit, I'd hate taking on loads of extra complexity for solving
> a niche issue.
>
> Comments?
Not sure, 2 or 3 seem valid. Is there a description of exactly what works
under 2? I haven't actually knowingly used signals under rump.
Justin
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