Re: [Xen-devel] [PATCH v2 3/3] libxl: ocaml: use 'for_app_registration' in osevent callbacks

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-12-16 at 11:35 +0000, Ian Campbell wrote:
> On Fri, 2013-12-13 at 18:04 +0000, Rob Hoes wrote:
> > On 13 Dec 2013, at 17:24, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> > > Rob Hoes writes ("[PATCH v2 3/3] libxl: ocaml: use 'for_app_registration' 
> > > in osevent callbacks"):
> > >> This allows the application to pass a token to libxl in the fd/timeout
> > >> registration callbacks, which it receives back in modification or
> > >> deregistration callbacks.
> > > ...
> > >> +        *for_app = caml_callbackN_exn(*func, 4, args);
> > >> +        if (Is_exception_result(*for_app)) {
> > >> +                ret = ERROR_OSEVENT_REG_FAIL;
> > >> +                goto err;
> > >> +        }
> > >> +
> > >> +        caml_register_global_root(for_app);
> > >> +        *for_app_registration_out = for_app;
> > >> +
> > >> +err:
> > >>  CAMLdone;
> > >>  caml_enter_blocking_section();
> > >> -        return 0;
> > >> +        return ret;
> > > 
> > > Doesn't this have the effect of throwing away the exception
> > > information ?  Perhaps it should be logged somewhere.
> > 
> > Thatâs true.
> 
> *for_app eventually ends up in a caller which is in the C bindings,
> doesn't it? Can it not be picked up there and reused with caml_raise
> after the appropriate C level cleanup?

Nevermind -- that eventual caller is just some random call down into
libxl...

> 
> > What would be the best way to do that? Can we get the logger from the
> > context in these stubs? If not, itâs going to be a little more
> > complicated... If we can, then still we need to add the ctx to the
> > âuserâ value that is passed around.
> > 
> > Rob
> 
> 
> 
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