Re: [Libguestfs] [nbdkit PATCH 1/2] rust: Implement can_cache

On 8/16/19 12:08 PM, Eric Blake wrote: Here, I was just copying what we had already done for the v1 fields that should remain unused (see above, in _pread_old for example). But is there a saner way to write a Rust struct that reserves the space required by the C ABI, but where the field MUST be left as NULL and not populated with Some(...) by the end user? Perhaps by marking the field const, while the rest of the struct is used as a mutable? (Doesn't change this patch, so much as a cleanup we could apply on top to prevent all of our _named fields from being overwritten after the initial construction with default values). And of course, if you want to actually implement extents, and figure out how to expose C-based nbdkit functions to be called by Rust code, be my guest (for .zero, we need nbdkit_set_error(), for extents, we need nbdkit_add_extent(), and then we have several other utility functions like nbdkit_realpath() that could be useful). -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org