Re: [Qemu-devel] Ignoring errno makes QMP errors suck

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 26 Mar 2012 16:04:26 +0200
Kevin Wolf <kwolf@redhat.com> wrote:

> >> Does the patch that you mentioned add a generic way for adding an
> >> (converted) errno to QMP errors? Or does it split up existing errors
> >> into more and finer grained errors?
> > 
> > The latter. The QMP errors have to be added manually. But it's just a matter
> > of time to get the most used errnos added.
> 
> Your PermissionDenied example doesn't really do this. It is a generic
> error message that may occur in multiple contexts, right? So in one
> context you may need a file name as additional information, in another
> context permission for something completely different may be missing
> (especially if you include EPERM in the same error).

Yes, but it's not a severe problem. Not yet. Because most of the time the
error context can be inferred from the command's context. Say, you fail to
create a file where only one file could be created.

But yes, we need to add a way for errors to accept optional parameters.

I have a series that's almost done that moves all errors to a qapi-error.json
file and auto-generates the QErrors tables. Maybe that's a first step towards
more flexible errors.

> I think 'OpenFileFailed' is not too bad, it's just missing a field that
> gives the detail 'PermissionDenied'. I'm not sure if having
> 'PermissionDenied' as the top-level error object is the best idea.

I think the end result is the same, but I prefer PermissionDenied as the
top level because it's slightly simpler.