Re: [Qemu-devel] [PATCH v2] mirror: drop local_err in mirror_complete

[Kevin Wolf]

Am 17.10.2013 um 14:49 hat Stefan Hajnoczi geschrieben:
> On Wed, Oct 16, 2013 at 08:56:49PM +0200, Max Reitz wrote:
> > On 2013-10-15 04:23, Fam Zheng wrote:
> > The reason I object it here is that error_propagate *currently* is a
> > no-op. But this may change in the future: I have already sent an RFC
> > which extends error_propagate so it can generate an error backtrace
> > if enabled through configure. If this (or something similar which
> > extends error_propagate to do more than basically just *errp =
> > local_err) is merged to/implemented in qemu later on, I believe we
> > want to call error_propagate in every function that touches an error
> > variable in order to generate a backtrace with maximum verbosity.
> 
> Did you check if glib's backtrace(3) APIs can be used in error_set()
> instead of rolling our own backtrace?
> 
> Also, what is the purpose of the backtrace?  If the problem is that
> error messages don't identify unique errors, then we should fix that
> instead of relying on backtraces.  For example, a function that opens
> two separate files shouldn't just fail with "File not found" since we
> don't know which of the two files wasn't found.

Mostly debugging, I guess. Even if you have unique error messages that
can only come from a single place, finding that single place by looking
at all called functions from a given QMP command can take quite a bit of
time. I can see it useful.

And we don't even have the unique error messages yet, so we shouldn't
fall in the trap of rejecting an improvement because it's not perfect.

Kevin