Re: [Libguestfs] [libnbd PATCH v3 03/22] protocol: Add definitions for extended headers

[Richard W.M. Jones]

On Tue, May 30, 2023 at 05:48:25PM +0200, Laszlo Ersek wrote:
> BTW I'm foreseeing a problem: if the extended block descriptor can
> provide an unsigned 64-bit length, we're going to have trouble exposing
> that in OCaml, because OCaml only has signed 64-bit integers. So that's
> going to reproduce the same issue, only for OCaml callers of the *new* API.
> 
> I can see Eric's series includes patches like "ocaml: Add example for
> 64-bit extents" -- I've not looked at those yet; for now I'm just
> wondering what tricks we might need in the bindings generator. The
> method seen in the "middle patch" above won't work; we don't have a
> native OCaml "i128" type for example that we could use as an escape
> hatch, for representing C's uint64_t.

I think that's OK because disk sizes are already limited to
2^63 - 1 by the kernel (and for qemu even less than that).
The OCaml bindings return a (signed) int64 for NBD.get_size.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
nbdkit - Flexible, fast NBD server with plugins
https://gitlab.com/nbdkit/nbdkit