Re: block-rbd: One function call less in rbd_dev_probe_parent() after error detection

[SF Markus Elfring <elfring@users.sourceforge.net>]

>> * Why was the function "rbd_dev_probe_parent" implemented in the way
>>   that it relies on a sanity check in the function "rbd_dev_destroy" then?
> 
> Because it's not a bad thing?

There are different opinions about this implementation detail.


> What's wrong with an init to NULL, a possible assignment, in this case
> from rbd_dev_create(), and an unconditional rbd_dev_destroy()?

Does this approach look like it is affected by a "one error jump
label bug" symptom?


> The NULL check in rbd_dev_destroy() is not a sanity check,
> it's a feature.

I have got an other impression here.


> It's not there to "fixup" callers that pass NULL

It seems that the explanations on the detail why a function tolerates
passed null pointers can also be different.


> - it's there because it is _expected_ that some callers will pass NULL.

I find it still unnecessary to let a called function like "rbd_dev_destroy"
to repeat the check when you know already that the passed variable contains
a null pointer.


> As I said in my reply to Dan, the problem with rbd_dev_probe_parent()
> is the calling code which expects it to call unparent if ->parent_spec.
> This makes it stand out and confuses people, but can't be fixed without
> refactoring a bunch of other code.

I would appreciate if the discussed function could be also improved by itself.
More refactoring might follow at other source code places later.


> The extra function call is *not* a problem.

How many software developers and reviewers will care if corresponding
error handling can also become a bit more efficient?

Regards,
Markus