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

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

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 <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);
>>>  }
>>>
>>>
>>
>