Re: [Qemu-devel] [PATCH] Fixes a bug that tries to use the unimplemented function fdatasync on Mac OS X.

[Alexander Graf]

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