Re: [Qemu-devel] [PATCH] scsi-generic: Simplify error handling code

[Paolo Bonzini]

On 18/01/2018 12:21, Philippe Mathieu-Daudé wrote:
>> I'm not a fan of bool return types, in general (because "!" is often
>> success while "< 0" is failure) and especially when there is an Error**;
>> I disagree with commit 9d3b155186.  But the function is not in an area I
>> maintain so I'm queuing this, thanks.
> Do you prefer "if (local_err)" and "if (errp && *errp)" ?

The latter is wrong.  I do prefer

    if (local_err) {
        error_propagate(errp, local_err);
        return;
    }

or maybe (but only if there is a meaning to a zero vs. positive return
value, or if errno is an important part of the returned Error *)

    ret = f(..., errp);
    if (ret < 0) {
        return;
    }

> I wondered once if a macro might improve this pattern but thought the
> code would get more obscure.

Eduardo had a series to avoid error_propagate, where NULL was replaced
by a (non-NULL) IGNORED_ERRORS macro.  Then you could do:

    f(..., errp);
    if (error_is_set(errp)) {
        return;
    }

See here:
https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg03139.html

Paolo