How about this:
static bool preadv_present = true;
static bool preadv_checked = false;
static ssize_t
qemu_preadv(int fd, const struct iovec *iov, int nr_iov, off_t offset)
{
#ifdef CONFIG_DARWIN
if (!preadv_checked) {
if (__builtin_available(macOS 11, iOS 14, watchOS 7, tvOS 14, *)) {
preadv_checked = true;
} else {
preadv_present = false;
return -ENOSYS;
}
}
#endif
return preadv(fd, iov, nr_iov, offset);
}
-j
On Fri, Nov 20, 2020 at 10:21 AM Philippe Mathieu-Daudé <f4...@amsat.org> wrote:
>
> On 11/20/20 4:49 PM, Joelle van Dyne wrote:
> > No, because if you build on a macOS 11 host but try to run it on macOS
> > 10.15 then it will crash.
>
> I'm not asking to move the check to configure/build time,
> but to do it only once at runtime...
>
> >
> > -j
> >
> > On Fri, Nov 20, 2020 at 4:32 AM Philippe Mathieu-Daudé <f4...@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);
> >>> }
> >>>
> >>>
> >>
> >
