> On 15 Sep 2016, at 13:23, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Thu, Sep 15, 2016 at 02:21:20PM +0200, Wouter Verhelst wrote: >> Right. So do I understand you correctly that blk-mq currently doesn't >> look at multiple queues, and just assumes that if a FLUSH is sent over >> any one of the queues, it applies to all queues? > > Yes. The same is true at the protocol level for NVMe or SCSI transports > that can make use of multiple queues. At an implementation level that is going to be a little difficult for some NBD servers, e.g. ones that fork() a different process per connection. There is in general no IPC to speak of between server instances. Such servers would thus be unsafe with more than one connection if FLUSH is in use. I believe such servers include the reference server where there is process per connection (albeit possibly with several threads). Even single process servers (including mine - gonbdserver) would require logic to pair up multiple connections to the same device. I suspect ALL nbd servers would require a change. So I think we should think carefully before introducing this protocol change. It might be easier to make the client code change work around this issue (somehow). -- 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
