Re: [PATCH v3 7/7] block: check availablity for preadv/pwritev on mac

[Joelle van Dyne]

If built with Xcode 11 (or below), a compile time error will occur due
to symbol not found. (QEMU's ./configure detects this and doesn't
enable it)
If built with Xcode 12 without the checks, a runtime error will occur.

-j

On Wed, Oct 28, 2020 at 5:23 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> On Tue, Oct 27, 2020 at 08:07:01PM -0700, Joelle van Dyne wrote:
> > 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.
> >
> > Signed-off-by: Joelle van Dyne <j@getutm.app>
> > ---
> >  block/file-posix.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
>
> What happens when preadv() is called prior to macOS 11/iOS 14?
>
> If I understand correctly the runtime check is preferrable because
> otherwise a binary compiled on recent macOS/iOS would ship with preadv()
> support but fail when executed on an older macOS/iOS?