On 10/17/22 17:17, Stefan Berger wrote: > > > On 10/17/22 09:48, Daniel P. Berrangé wrote: >> On Mon, Oct 17, 2022 at 09:39:52AM -0400, Stefan Berger wrote: >>> >>> > >> >> The key is in qemuMigrationSrcIsSafe(), and how it determines if a >> migration is safe. >> >> * Disk on local storage, no flags => unsafe, migration error >> * Disk on local storage, VIR_MIGRATE_NON_SHARED_DISK => ok, copies >> disk storage >> * Disk on shared storage, no flags => safe >> * Disk on shared storage, VIR_MIGRATE_NON_SHARED_DISK => ok, but >> needlessly copies disk storage >> >> The key helper methods are virFileIsSharedFS and virFileIsClusterFS >> which check the filesystem type for the path against a known list >> of shared/cluster FS. >> >>> So we won't do it this way for TPM state migration. Instead we can >>> try to write on the source migration side >>> >>> a) a simple file and detect whether the file is at the destination >>> b) a file with either a name or content that only the source and >>> destination libvirts would know at this point >>> >>> b) is to prevent stale files from becoming indicators for shared >>> storage. >> >> No, please use the virFileIsSharedFS/ClusterFS helpers. >> > > I tried to use virFileIsSharedFS on the source and destination side of > my NFS setup to see how they work. The issue here is that the NFS server > side, that exports /var/lib/libvirt/swtpm and is also the migration > source at some point, says this: > > /var/lib/libvirt/swtpm/ecc221c4-6bb9-423f-ac31-72244fdbb1a1/tpm2 is > shared: 0 > > the NFS client side then says this: > > > /var/lib/libvirt/swtpm/ecc221c4-6bb9-423f-ac31-72244fdbb1a1/tpm2 is > shared: 1 > Are both sides mounted as NFS or just one of them? I think it's safe to assume that either both sides are on a shared FS or none. Otherwise I'm quite sure file locking won't work anyways. We can go even further and test whether shared_fs(source) == shared_fs(dst); and throw an error if it doesn't. And since I've misguided you on the way with flag I am willing to help you write patches. Please let me know if you need any help. Michal
