On Thu, Sep 15, 2016 at 01:11:24PM +0100, Alex Bligh wrote: > > NBD_CMD_FLUSH (3) > > > > A flush request; a write barrier. > > I can see that's potentially confusing as isn't meant to mean 'an old-style > linux kernel block device write barrier'. I think in general terms it > probably is some form of barrier, but I see no problem in deleting the > words "a write barrier" from the spec text if only to make it > clearer. Yes, please do that. A "barrier" implies draining of the queue. > However, I think the description of the command itself: > > > The server MUST NOT send a successful reply header for this request before all write requests for which a reply has already been sent to the client have reached permanent storage (using fsync() or similar). > > and the ordering section I pointed you to before, were both correct, yes? Yes, this seems correct. > actually fdatasync() technically does more than is necessary, as it > will also flush commands that have been processed, but for which no > reply has yet been sent - that's no bad thing. Yes. But without an actual barrier it's hard to be exact - and fdatasync does the right thing by including false positives. -- 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
