On Tue, Apr 14, 2015 at 11:22:41AM -0700, Zach Brown wrote: > On Tue, Apr 14, 2015 at 02:19:11PM -0400, J. Bruce Fields wrote: > > On Tue, Apr 14, 2015 at 01:16:13PM -0400, Anna Schumaker wrote: > > > On 04/14/2015 12:53 PM, Christoph Hellwig wrote: > > > > On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote: > > > >> Yuck! How the heck do you clean up the mess if that happens? I > > > >> guess you're just stuck redoing the copy with normal READ/WRITE? > > > >> > > > >> Maybe we need to have the interface return a hard error in that > > > >> case and not try to give back any sort of offset? > > > > > > > > The NFSv4.2 COPY interface is a train wreck. At least for Linux I'd > > > > expect us to simply ignore it and only implement my new CLONE > > > > operation with sane semantics. That is unless someone can show some > > > > real life use case for the inter server copy, in which case we'll > > > > have to deal with that mess. But getting that one right at the VFS > > > > level will be a nightmare anyway. > > > > > > > > Make this a vote from me to not support partial copies and just > > > > return and error in that case. > > > > > > Agreed. Looking at the v4.2 spec, COPY does take ca_consecutive and a > > > ca_synchronous flags that let the client state if the copy should be > > > done consecutively or synchronously. I expected to always set > > > consecutive to "true" for the Linux client. > > > > That's supposed to mean results are well-defined in the partial-copy > > case, but I think Christoph's suggesting eliminating the partial-copy > > case entirely? > > > > Which would be fine with me. > > > > It might actually have been me advocating for partial copies. But that > > was only because a partial-copy-handling-loop seemed simpler to me than > > progress callbacks if we were going to support long-running copies. > > > > I'm happy enough not to have it at all. > > Ah, OK, that's great news. > > I thought at one point we were worried about very long running RPCs on > the server. Are we not worried about that now? > > Is the client expected to cut the work up into arbitrarily managable > chunks? Is the server expected to fail COPY/CLONE requests that it > thinks would take way too long? Something else? Christoph is proposing a CLONE rpc that's required to be atomic: https://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-35#section-15.13 "The CLONE operation is atomic, that is either all changes or no changes are seen by the client or other clients." So that couldn't be really long-running (or the server is nuts). So that'd mean Anna would rip out the server-side copy loop and we'd initially just support btrfs or whatever. I mean the server-side copy loop may also be useful but I'm all for wiring up the obvious case first. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
