From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 23 Mar 2021 15:00:52 +0000 From: "Dr. David Alan Gilbert" Message-ID: References: <714BD741-AE3F-4BC5-8DFB-F5C74A8623B1@netapp.com> <20210323145312.GB483930@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210323145312.GB483930@redhat.com> Subject: Re: [Virtio-fs] Live migration support for virtio-fs List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vivek Goyal Cc: "virtio-fs@redhat.com" , "Ge, Xiongzi" * Vivek Goyal (vgoyal@redhat.com) wrote: > On Tue, Mar 23, 2021 at 10:29:09AM +0000, Dr. David Alan Gilbert wrote: > > * Ge, Xiongzi (Xiongzi.Ge@netapp.com) wrote: > > > Hello Vivek, Dr. Gilbert, and the virtio-fs team, > > > > Hi Xiongzi, > > > > > It seems that virtio-fs does not support live migration. Once a vm > > > is configured with virtio-fs, live migration cannot be performed even > > > it is not mounted on the guest. > > > > Right. > > > > > Is there any progress for this? > > > > Max Reitz is looking at some parts of it; in particular storing file > > handles that can later be reopened. > > But there are a bunch of other parts we've not looked at yet either > > (like the dirty page marking around all syscalls). > > > > > If the > > > shared directory is from a distributed file system like Ceph, would it > > > be easier than the general case to be implemented? > > > > Maybe; there are some tricky semantics problems; for example, lets > > imagine that you open the file 'a/b/c' on the source, and sometime > > after you open it, 'b' gets renamed to 'd'; when you resume on the > > destination you need to make sure you know how to get to that file. > > Depending on the filesystem semantics you might need to make that work > > even if 'a/b/c' had been deleted but you still had it open. > > Hi Dave, > > I am assuming that with file handles, renaming of file probably is not > a problem. open_by_handle_at() will still be able to find it. Right; although again with soemthing like CEPH you might not even need that if you had a virtiofs daemon that spoke direct to CEPH, you might be dealing with a CEPH filehandle. > I think real problem (as you pointed out later) is unliked file which is > still in use by the virtiofsd. Dave > Thanks > Vivek -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK