Re: [Qemu-devel] Heads up: glibc preadv emulation breaks qemu on older kernels

[Anthony Liguori]

On 02/12/2010 07:50 AM, Christoph Hellwig wrote:
> On Fri, Feb 12, 2010 at 04:49:23PM +0300, malc wrote:
>    
> > On Fri, 12 Feb 2010, Christoph Hellwig wrote:
> >
> >      
> > > On Thu, Feb 11, 2010 at 07:06:08PM +0000, Richard W.M. Jones wrote:
> > >        
> > > > One interesting thing is that qemu has its own preadv emulation (which
> > > > does the emulation correctly), but this is never used because qemu
> > > > never gets ENOSYS back from preadv.
> > > >          
> > > At this point the amount of bugs in the glibc preadv/pwritev code really
> > > make me want to go to use the raw system calls on Linux only.  Any
> > > opinions from the maintainers if that is acceptable?
> > >        
> > There are more than one way to parse the first sentence, if it should be
> > read as:
> >    On linux and on linux only avoid using pread/write[v] and talk to the
> >    kernel directly.
> >
> > Then i agree.
> >      
> Yes.  The BSDs tend to not play stupid emulation games in the libc, so
> changes of these kinds of messups to happen are far less.
>    

In all fairness, I seem to recall there being a problem with the kernel 
implementation of preadv/pwritev too.

I think a configure option would be in order.  Forever avoiding glibc is 
probably a bit extreme.

Regards,

Anthony Liguori

>