On Thu, May 25, 2017 at 9:30 PM, Haozhong Zhang <haozhong.zh...@intel.com> wrote: > On 05/25/17 20:34 -0700, Dan Williams wrote: >> On Thu, May 25, 2017 at 7:32 PM, Haozhong Zhang >> <haozhong.zh...@intel.com> wrote: >> > Applications in Linux guest that use device-dax never trigger flush >> > that can be trapped by KVM/QEMU. Meanwhile, if the host backend is not >> > device-dax, QEMU cannot guarantee the persistence of guest writes. >> > Before solving this flushing problem, QEMU should warn users if the >> > host backend is not device-dax. >> >> I think this needs to be stronger than a "warn" it needs to be >> explicitly forbidden when it is known to be unsafe. >> > > I understand your worry and am not object to your suggestion, but > forbidden will change the existing behavior that allows such unsafe > usage. Let's wait for other maintainers' comments.
Changing existing behavior is the point. Even if a qemu maintainer thought it was acceptable to allow the dangerous behavior with a warning I would continue to assert that we need to block it by default. I'm not opposed to adding a new configuration option like "allow dangerous pmem" to override the new default behavior, but I think this patch is incorrect to just emit a message.
