Re: fall back from direct to buffered I/O when stable writes are required

Johannes Thumshirn
2025-11-06T09:50:20Z

On 11/5/25 10:44 PM, Darrick J. Wong wrote:
> Just out of curiosity -- is qemu itself mutating the buffers that it is
> passing down to the lower levels via dio? Or is it a program in the
> guest that's mutating buffers that are submitted for dio, which then get
> zerocopied all the way down to the hypervisor?

If my memory serves me right it is the guest (or at least can be). I
remember a bug report on btrfs where a Windows guest had messed up
checksums because of modifying inflight I/O.