Am 11.11.2011 15:03, schrieb Anthony Liguori: > On 11/11/2011 04:15 AM, Kevin Wolf wrote: >> Am 10.11.2011 22:30, schrieb Anthony Liguori: >>> Live migration with qcow2 or any other image format is just not going to work >>> right now even with proper clustered storage. I think doing a block level flush >>> cache interface and letting block devices decide how to do it is the best approach. >> >> I would really prefer reusing the existing open/close code. It means >> less (duplicated) code, is existing code that is well tested and doesn't >> make migration much of a special case. > > Just to be clear, reopen only addresses image format migration. It does not > address NFS migration since it doesn't guarantee close-to-open semantics. Yes. But image formats are the only thing that is really completely broken today. For NFS etc. we can tell users to use cache=none/directsync and they will be good. There is no such option that makes image formats safe. > The problem I have with the reopen patches are that they introduce regressions > and change at semantics for a management tool. If you look at the libvirt > workflow with encrypted disks, it would break with the reopen patches. Yes, this is nasty. But on the other hand: Today migration is broken for all qcow2 images, with the reopen it's only broken for encrypted ones. Certainly an improvement, even though there's still a bug left. >> If you want to avoid reopening the file on the OS level, we can reopen >> only the topmost layer (i.e. the format, but not the protocol) for now >> and in 1.1 we can use bdrv_reopen(). > > I don't view not supporting migration with image formats as a regression as it's > never been a feature we've supported. While there might be confusion about > support around NFS, I think it's always been clear that image formats cannot be > used. > > Given that, I don't think this is a candidate for 1.0. Nobody says it's a regression, but it's a bad bug and you're blocking a solution for it for over a year now because the solution isn't perfect enough in your eyes. :-( Kevin -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
