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

[Stefan Hajnoczi]

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.

Stefan