Re: [PATCH v2 9/9] block: check availablity for preadv/pwritev on mac

[Thomas Huth]

On 20/10/2020 00.20, Joelle van Dyne wrote:
> On Mon, Oct 19, 2020 at 1:27 AM Thomas Huth <thuth@redhat.com> wrote:
>>
>> On 19/10/2020 03.39, Joelle van Dyne wrote:
>>> From: osy <osy86@users.noreply.github.com>
>>
>> That "From:" line looks wrong ... could you please fix the "Author" of your
>> patches / your git config?
> osy wrote the original changes. I joined the UTM project to help bring
> the changes upstream with permission. However, they have agreed that
> if required that we can use my name as the author.

In any way, that "users.noreply.github.com" does not look like a valid
e-mail address and should be replaced.

>>
>>> macOS 11/iOS 14 added preadv/pwritev APIs. Due to weak linking, configure
>>> will succeed with CONFIG_PREADV even when targeting a lower OS version. We
>>> therefore need to check at run time if we can actually use these APIs.
>>
>> That sounds like the wrong approach to me ... could you please try to fix
>> the check in "configure" instead? E.g. by running compile_prog with
>> "-Werror", so that the test fails if there is no valid prototype available?
> It's not that simple. Xcode 11 and below (supporting macOS 10.15 and
> below, iOS 13 and below, etc) does not have preadv/pwritev symbols
> defined and would fail to compile. Xcode 12 (supporting macOS 11 and
> below, iOS 14 and below, etc) have preadv/pwritev weakly defined so if
> it runs on, for example, 10.15, it would abort. There is no way to
> determine at compile time if you can use preadv/pwritev or not when
> building with Xcode 12. The availability checks are Apple's preferred
> way to handle this kind of situation (they discourage directly
> checking if an API exists on a system).

Ok, got it now, thanks for the detailed explanation!

 Thomas