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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-12-12 at 21:27 +0000, Rob Hoes wrote:
> > If it indicates an error in the caller of the bindings or something
> > which can happen for some reason unrelated to the code itself (e.g some
> > external circumstance) then the error return would be appropriate.
> 
> For the modify and deregister functions, Iâd consider it a programming
> error if for_app is NULL (either in the bindings or libxl itself).
> This is because the register functions will always get a value passed
> in from the OCaml app (even if it is just a unit â()â), and this value
> is expected to be delivered to subsequent (related) modify or
> deregister calls.
> 
> Following your reasoning, we should use an assert for this.

Agreed.

> For the register functions, for_app_registration_out is NULL on entry
> (according to libxl_event.h), but this is ignored by the bindings.
> There is an âif (for_app)â there to check the outcome of malloc. If
> malloc returns NULL, then the second category applies (external
> circumstance). According to the docs, a registration of modification
> hook may return ERROR_OSEVENT_REG_FAIL or any positive int in case it
> fails, which seems appropriate there.

Right, I should have been clearer that I was talking about the other
case and not the allocation failures.

> Iâll update the patch.

Thanks,
Ian.



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