Re: [PATCH v2 2/9] qemu: Introduced VIR_MIGRATE_TPM_SHARED_STORAGE for TPM migration

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