> On 15 Sep 2016, at 12:40, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Thu, Sep 15, 2016 at 01:29:36PM +0200, Wouter Verhelst wrote: >> Yes, and that is why I was asking about this. If the write barriers >> are expected to be shared across connections, we have a problem. If, >> however, they are not, then it doesn't matter that the commands may be >> processed out of order. > > There is no such thing as a write barrier in the Linux kernel. We'd > much prefer protocols not to introduce any pointless synchronization > if we can avoid it. I suspect the issue is terminological. Essentially NBD does supports FLUSH/FUA like this: https://www.kernel.org/doc/Documentation/block/writeback_cache_control.txt IE supports the same FLUSH/FUA primitives as other block drivers (AIUI). Link to protocol (per last email) here: https://github.com/yoe/nbd/blob/master/doc/proto.md#ordering-of-messages-and-writes -- Alex Bligh -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
