On Tue, Sep 20, 2016 at 05:49:17PM +0200, Peter Krempa wrote: > On Tue, Sep 20, 2016 at 15:21:16 +0100, Daniel Berrange wrote: > > On Tue, Sep 20, 2016 at 03:53:16PM +0200, Peter Krempa wrote: > > > On Tue, Sep 20, 2016 at 09:40:22 -0400, Corey S. McQuay wrote: > > > > Currently Libvirt allows attempts to migrate read only disks. Qemu cannot handle this as read only > > > > disks cannot be written to on the destination system. The end result is a cryptic error message > > > > and a failed migration. > > > > > > This is not necessarily true. Read only disks can sometimes be in fact > > > backed by storage that is writable and it's desired to be migrated. > > > > If 'def->readonly' is true, then the security drivers won't allow > > QEMU to write to the image, regardless of whether the underlying > > storage is writable. > > That definitely would be just a bug in the implementation rather than a > reason to do this. That's not a bug - that's a feature - if the disk is marked readonly, SELinux is right to prevent QEMU writing to the disk. > In fact the problem is that qemu itself forbids to write the data to a > readonly marked block backend, which indeed makes this impossible > although I'm pretty certain that it worked for me in some configuration. That's a further layer of protection/complication, but I'm concerned primarily about fact that libvirt is intentionally blocking writes > At any rate, checking this on the source of migration is incorrect. The > destination should do such check if there's currently no way to persuade > qemu do do it. We still may later find a way and all hosts running older > versions would be hosed. So the check would belong in qemuMigrationStartNBDServer, rather than in the DriveMirror method Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list