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

[Rob Hoes <Rob.Hoes@xxxxxxxxxx>]

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.

That’s true.

What would be the best way to do that? Can we get the logger from the context 
in these stubs? If not, it’s going to be a little more complicated... If we 
can, then still we need to add the ctx to the “user” value that is passed 
around.

Rob
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