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

[Philippe Mathieu-Daudé]

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);
>  }
>  
>