> The NBD spec states that since trim requests can affect disk contents,
> then they should allow for FUA semantics just like writes for ensuring
> the disk has settled before returning. As bdrv_[co_]pdiscard() does
> not (yet?) support a flags argument, we can't pass FUA down the block
> layer stack, and must therefore emulate it with a flush at the NBD
TRIM requests should not need FUA since they're just advisory. On
the other hand, WRITE ZEROES requests need to support FUA.