On Thu, Oct 05, 2006 at 06:06:26PM +0000, Thor Lancelot Simon wrote:
> On Thu, Oct 05, 2006 at 02:48:33PM +0000, Chuck Silvers wrote:
> > 
> > Log Message:
> > add support for O_DIRECT (I/O directly to application memory,
> > bypassing any kernel caching for file data).
> 
> Like Rui said, thanks!
> 
> How hard would it be to convert vnd to use direct I/O?  It seems like
> that would fix some annoying double-caching problems (and a lot more
> people actually use vnd on production systems now because it is a
> convenient backing store for Xen virtuals).
> 
> If it's just mechanical changes, let me know what they are, and I will
> have a shot at it if I can find the time this weekend.
> 
> Thor

Looks like it is not ready yet (from sys/miscfs/genfs/genfs_vnops.c):

    void
    genfs_directio(struct vnode *vp, struct uio *uio, int ioflag)
    ...
           /*
            * We only support direct I/O to user space for now.
            */

           if (VMSPACE_IS_KERNEL_P(uio->uio_vmspace)) {
                   return;
           }

and fss would need it too :-)

--
Juergen Hannken-Illjes - hannken@eis.cs.tu-bs.de - TU Braunschweig (Germany)