Re: [Qemu-devel] [PATCH] nbd/server: Honor FUA request on NBD_CMD_TRIM

[Paolo Bonzini]

> 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
> layer.

TRIM requests should not need FUA since they're just advisory.  On
the other hand, WRITE ZEROES requests need to support FUA.

Paolo