Re: [Xen-devel] [RFC v5 024/126] error: auto propagated local_err

[Eric Blake <eblake@xxxxxxxxxx>]

On 11/8/19 3:10 PM, Marc-André Lureau wrote:

> > +/*
> > + * ERRP_AUTO_PROPAGATE
> > + *
> > + * This macro is created to be the first line of a function with Error **errp
> > + * OUT parameter. It's needed only in cases where we want to use error_prepend,
> > + * error_append_hint or dereference *errp. It's still safe (but useless) in
> > + * other cases.
> > + *
> > + * If errp is NULL or points to error_fatal, it is rewritten to point to a
> > + * local Error object, which will be automatically propagated to the original
> > + * errp on function exit (see error_propagator_cleanup).
> > + *
> > + * After invocation of this macro it is always safe to dereference errp
> > + * (as it's not NULL anymore) and to add information (by error_prepend or
> > + * error_append_hint)
> > + * (as, if it was error_fatal, we swapped it with a local_error to be
> > + * propagated on cleanup).
> Nice improvements. Minor drawback, the abort()/exit() will now take
> place when going out of scope and running the cleanup instead of error
> location. Not a big problem I guess.
Your assessment is not quite right:

Any abort() will happen at the leaf node (because we are no longer 
wrapping thing into a local err and skipping error_propagate altogether 
for &error_abort).
You are correct that any exit() will now happen during cleanup, but that 
is an undetectable change (there is no stack trace present for 
&error_fatal, so calling error_propagate at a later point in time does 
not affect the observable end behavior).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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