Re: [PATCH] kvm: add detail error message when fail to add ioeventfd

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, May 22, 2013 at 09:48:21PM +0800, Amos Kong wrote:
> On Wed, May 22, 2013 at 11:32:27AM +0200, Stefan Hajnoczi wrote:
> > On Wed, May 22, 2013 at 12:57:35PM +0800, Amos Kong wrote:
> > > I try to hotplug 28 * 8 multiple-function devices to guest with
> > > old host kernel, ioeventfds in host kernel will be exhausted, then
> > > qemu fails to allocate ioeventfds for blk/nic devices.
> > > 
> > > It's better to add detail error here.
> > > 
> > > Signed-off-by: Amos Kong <akong@redhat.com>
> > > ---
> > >  kvm-all.c |    4 ++++
> > >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > It would be nice to make kvm bus scalable so that the hardcoded
> > in-kernel I/O device limit can be lifted.
> 
> I had increased kernel NR_IOBUS_DEVS to 1000 (a limitation is needed for
> security) in last Mar, and make resizing kvm_io_range array dynamical.

The maximum should not be hardcoded.  File descriptor, maximum memory,
etc are all controlled by rlimits.  And since ioeventfds are file
descriptors they are already limited by the maximum number of file
descriptors.

Why is there a need to impose a hardcoded limit?

Stefan