Re: Error reporting should be improved

[Peter Rosin]

Den 2009-12-29 23:09 skrev Bob Friesenhahn:
> On Tue, 29 Dec 2009, Peter Rosin wrote:
> > > This is because the last error was overridden by the subsequent 
> > > tries. Maybe we should stop trying once the right file was found. 
> > > This way the right message could be given to user.
> >
> > The trouble is that it is not dlopen that gives this message, it is
> > dlerror that gives the message, and it would be terrible to use
> > string comparison to dig out the cause of the failure. And that's
> > just for the dlopen loader, who knows how the other loaders behave
> > on obscure systems in wierd corner cases. Finding a reliable way
> > to catch all errors that are not "file not found" or equivalent
> > and quit early will not be an easy task.
> >
> > The loaders typically just report CANNOT_OPEN when something fails,
> > and the ltdl core has no reliable way of knowing the underlying
> > cause.
>
> Errors from the preopen loader can be overwritten, but the first error 
> reported subsequent to the preopen loader should be retained.  It seems 
> like what we need is a flag that indicates if the error is allowed to be 
> overwritten.  The alternative is error message concantenation, but that 
> might lead to ugly results.

I'm just saying that it is not going to be easy to deduce if an
error is allowed to be overwritten.

Have a look at libltdl/loaders/dlopen.c:vm_open(). It basically
calls dlopen and sets the error to CANNOT_OPEN if dlopen fails.
The ways I see to dig out the underlying failure is to either call
dlerror and parse the string (Eeek!) or replicate the dlopen
internals and arrive at the same cause as dlopen did (EEEK!).

Not fun at all.

Cheers,
Peter

--
They are in the crowd with the answer before the question.
> Why do you dislike Jeopardy?