Re: [Libguestfs] [libnbd] More thoughts on callbacks and more

On 7/22/19 6:50 AM, Richard W.M. Jones wrote: > On Mon, Jul 22, 2019 at 10:08:25AM +0100, Richard W.M. Jones wrote: >> On Sat, Jul 20, 2019 at 07:38:45AM +0100, Richard W.M. Jones wrote: >>> More thoughts on callbacks, etc. following on from: >>> https://www.redhat.com/archives/libguestfs/2019-July/thread.html#00184 >>> >>> Closure lifetimes >>> ----------------- > > Here's a possibly better idea which still changes the API a bit but > not as invasively. > > We overload the callback so that it can either be a callback function > or a "free function". They are distinguished by an extra flag > argument passed to the callback: > > extern int nbd_set_debug_callback ( > struct nbd_handle *h, > int (*debug_fn) (int valid_flag, // <-- note > void *user_data, > const char *context, const char *msg), > void *user_data); Would the 'valid_flag' be presented to non-C bindings, or is it only needed for C code?

At any rate, the idea makes sense as a lighter-weight way for libnbd to always inform the callback about the last invocation.