Re: [Libguestfs] [nbdkit PATCH 0/2] bind .zero to more languages

On 01/24/2017 09:41 AM, Richard W.M. Jones wrote: > On Tue, Jan 24, 2017 at 03:16:45PM +0000, Richard W.M. Jones wrote: >> However we could add another API: >> >> nbdkit_set_errno (int errno); >> >> This allows the plugin to send the errno back to the core code >> explicitly. It's effectively stored as a global in the core code. > > What I'm really saying here is that at the moment (after your previous > patch series) we have an implicit channel where errno is passed from > the plugin to the core code. We should simply make that channel > explicit and controlled by the plugin. Sounds reasonable. Do we really want plugins to report the full range of errno (using POSIX::errno in your perl example), or do we want the plugins to expose a new enum, with just the 5 or 6 errno values actually supported by the NBD protocol? I'm leaning towards each binding providing an enum of just the supported error values, in an nbd_ namespace, rather than tying directly to system errno values.

Also, the NBD spec DOES allow for the server to send a string error message alongside the error code; we aren't utilizing that yet, but it would be worth exploring how easy it would be to let the plugin's error message be reflected through to the client.