Re: [libvirt] [PATCH 03/20] virConnect(Un)RegisterCloseCallback: Throw an error in case the API is not supported

Report an error in case the driver does not support connect(Un)registerCloseCallback. The commit 'close callback: move it to driver' (88f09b75eb99) moved the responsibility for the close callback to the driver. But if the driver doesn't support the connectRegisterCloseCallback API this function does nothing, even no unsupported error report. The only case where an error is reported is when the API is supported but the call fails. The same behavior applies to virConnectUnregisterCloseCallback. This behavior is not intended as there are many use cases of this API where the state of for example allocations depends on the result of these functions. To keep the behavior of virsh as before it must silently ignore unsupported error for virConnectRegisterCloseCallback. For the remote driver this change wouldn't be needed, but for the byhve driver, for example. Otherwise the user would see the error message that virsh was unable to register a disconnect callback.