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

[Eric Blake]

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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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