On 06/13/2017 05:55 AM, Kevin Wolf wrote: > > We could possibly make read-zeroes a mandatory option in QAPI > (currently it seems it doesn't even exist - oops!) and if we really want > to print warnings for -drive, do it only if the default is used so that > passing an explicit read-zeroes=off removes the warning. Or we could > make it mandatory there, too.
I'm late to the conversation, but I like this approach... > > These changes are incompatible, but I think the null-* use cases are > mostly about testing and debugging, so I feel we can be a bit laxer > about compatibility (like we already are with blkdebug). Since null-co is a debug-only interface, I'm not as worried about backwards-compatibility, and making the option mandatory forces clients that are debugging to be explicit on whether they want defined reads or fast behavior. Once the option is mandatory, then it is also feasible to use valgrind macros to unconditionally shut up the warning about uninitialized reads, even when we are intentionally not zeroing the memory, because at that point the request for fast behavior is intentional. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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