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Re: [Qemu-devel] [PATCH] Fixes a bug that tries to use the unimplemented
From: |
Pierre Riteau |
Subject: |
Re: [Qemu-devel] [PATCH] Fixes a bug that tries to use the unimplemented function fdatasync on Mac OS X. |
Date: |
Thu, 10 Dec 2009 17:49:41 +0100 |
On 9 déc. 2009, at 00:01, Alexander Graf wrote:
>
> Am 08.12.2009 um 19:35 schrieb Blue Swirl <address@hidden>:
>
>> On Tue, Dec 8, 2009 at 4:35 PM, Pierre Riteau <address@hidden> wrote:
>>> On 1 oct. 2009, at 18:13, Blue Swirl wrote:
>>>
>>>> On Thu, Oct 1, 2009 at 6:30 PM, G 3 <address@hidden> wrote:
>>>>> On Sep 30, 2009, at 3:16 PM, Anthony Liguori wrote:
>>>>>
>>>>> G 3 wrote:
>>>>>
>>>>> This patch fixes a problem in the file cutils.c that prevents qemu from
>>>>> being built on Mac OS X. This patch makes sure fsync is used instead.
>>>>>
>>>>> What is this against? It doesn't apply to git.
>>>>>
>>>>> This is against the savannah
>>>>> repository: git://git.savannah.nongnu.org/qemu.git. Is this the wrong
>>>>> repository?
>>>>
>>>> The patch should not be needed since
>>>> 5f6b9e8fd5b9516170e582d9b6c27c98519a8031. Do you still have a problem?
>>>
>>> Sorry to dig up this old thread, but I just tried compiling qemu on my Mac
>>> and I see a warning when it compiles:
>>> cutils.c: In function ‘qemu_fdatasync’:
>>> cutils.c:128: warning: implicit declaration of function ‘fdatasync’
>>>
>>> I'm running OS X 10.6.2 with Xcode 3.2.1.
>>>
>>> Why this behavior? Because the configure check introduced in 5f6b9e finds
>>> that fdatasync is available.
>>> Although the fdatasync function is not referenced in the standard includes
>>> (hence the warning), it is present as a syscall:
>>> /usr/include/sys/syscall.h:#define SYS_fdatasync 187
>>> Moreover, a fdatasync symbol is available through libSystem (which is why
>>> the linking done by the configure check works).
>>>
>>> It's not clear what is the best solution here. Googling the issue, some
>>> projects add the fdatasync prototype to their headers to avoid warnings.
>>> Other assume that fdatasync could be a noop and fall back to fsync.
>>>
>>> I would go with the second second: the function is not defined, there is no
>>> man page, let's assume it doesn't work.
>>> To fix the configure check we can simply add -Werror to the compile_prog
>>> cflags (I will send a patch if you agree with this).
>>
>> I'd rather add something like
>> #ifdef __APPLE__
>> exit(1);
>> #endif
>> (or the shell equivalent for configure) and a comment with your explanation.
>>
>>
>
>
> I guess that's wrong. With --disable-werror it compiles just fine. So I think
> we're rather missing a header include.
>
> Alex
Compiling just fine doesn't necessarily mean thatt qemu will run fine and do
what we want it to do.
But in this case it may: i took a look at the XNU sources (I didn't think about
this solution first, I forgot it was open source...) and fdatasync appears to
be implemented.
So I guess that we can probably add the missing prototype in one of our header?
--
Pierre Riteau -- http://perso.univ-rennes1.fr/pierre.riteau/