[Qemu-devel] Re: [PATCH] kvm: Fix error detection for KVM_GET_DIRTY_LOG

[Alexander Graf]

Am 22.07.2009 um 22:07 schrieb Jan Kiszka <address@hidden>:

> Anthony Liguori wrote:
> > Jan Kiszka wrote:
> > > > That makes me uncomfortable.  Shouldn't we make kvm return  
> > > > something
> > > > that's exposed to userspace?
> > >
> > > Yes, but we can't do this from user space :) (or in other words:  
> > > there
> > > are already kernels out there which return this invalid code).
> >
> > But since it's not symbolic, at some point in time the meaning of 524
> > can potentially change and introduce a very, very subtle bug.
>
> I won't change in old kernel versions, and I expect someone from the  
> PowerPC folks to fix it for new version fairly soon.
>
> > > The situation would only be different if Alex said that it takes  
> > > further
> > > kernel patches anyway to make his PowerPC targets work. Dunno.
> >
> > Certainly, his PPC target is not in any released kernel version so
> > there's time to fix things properly.
>
> Ah, ok. Then let's do this (Alex can carry a temporary workaround
> locally IMHO):
>
> ------------->
>
> Signed-off-by: Jan Kiszka <address@hidden>
> ---
>
> kvm-all.c |    2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index 824bb4c..5fb8dba 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -348,7 +348,7 @@ int kvm_physical_sync_dirty_bitmap 
> (target_phys_addr_t start_addr,
>         d.slot = mem->slot;
>
>         r = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
> -        if (r == -EINVAL) {
> +        if (r < 0) {

That's worse as it essentially removes the not implemented case.

The only thing I'd agree with as a good idea instead of the version I  
sent is an explicit switch statement with an include of errno.h with  
__KERNEL__ set.

Alex


>             dprintf("ioctl failed %d\n", errno);
>             ret = -1;
>             break;