Re: [PATCH v5 7/7] block: check availablity for preadv/pwritev on mac

[Joelle van Dyne]

No, because if you build on a macOS 11 host but try to run it on macOS
10.15 then it will crash.

-j

On Fri, Nov 20, 2020 at 4:32 AM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 11/9/20 12:24 AM, 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(+)
> >
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index d83219df55..a9d69746a0 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1394,12 +1394,24 @@ static bool preadv_present = true;
> >  static ssize_t
> >  qemu_preadv(int fd, const struct iovec *iov, int nr_iov, off_t offset)
> >  {
> > +#ifdef CONFIG_DARWIN /* preadv introduced in macOS 11 */
> > +    if (!__builtin_available(macOS 11, iOS 14, watchOS 7, tvOS 14, *)) {
>
> Can we change the CONFIG_PREADV ifdef'ry to run this check once
> on macOS 11?
>
> > +        preadv_present = false;
> > +        return -ENOSYS;
> > +    } else
> > +#endif
> >      return preadv(fd, iov, nr_iov, offset);
> >  }
> >
> >  static ssize_t
> >  qemu_pwritev(int fd, const struct iovec *iov, int nr_iov, off_t offset)
> >  {
> > +#ifdef CONFIG_DARWIN /* pwritev introduced in macOS 11 */
> > +    if (!__builtin_available(macOS 11, iOS 14, watchOS 7, tvOS 14, *)) {
> > +        preadv_present = false;
> > +        return -ENOSYS;
> > +    } else
> > +#endif
> >      return pwritev(fd, iov, nr_iov, offset);
> >  }
> >
> >
>