[libvirt] [PATCH v4 3/9] qemuMigrationDriveMirror: Force raw format for NBD

From: Michal Privoznik <mprivozn(a)redhat.com&gt; When playing with disk migration lately, I've noticed this warning in domain logs: WARNING: Image format was not specified for 'nbd://masina:49153/drive-virtio-disk0' and probing guessed raw. Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted. Specify the 'raw' format explicitly to remove the restrictions. So I started digging into qemu source code to see what has triggered the warning. I'd expect qemu to know formats of guest's disks since we tell them on command line. This lead me to qmp_drive_mirror() where the following can be found: if (!has_format) { format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name; } So, format is automatically initialized from the disk iff mode != "existing". Unfortunately, in migration we are tied to use this mode (NBD doesn't support creating new images). Therefore the only way to avoid this warning is to pass format. The discussion on the mail-list [1] resulted in the code that always forces NBD export as "raw" format. [1] https://www.redhat.com/archives/libvir-list/2015-June/msg00153.html Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; Signed-off-by: Pavel Boldin <pboldin(a)mirantis.com&gt; --- src/qemu/qemu_migration.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c index 6c94052..1fa5e5f 100644 --- a/src/qemu/qemu_migration.c +++ b/src/qemu/qemu_migration.c @@ -1966,8 +1966,9 @@ qemuMigrationDriveMirror(virQEMUDriverPtr driver, goto cleanup; } + /* Force "raw" format for NBD export */ mon_ret = qemuMonitorDriveMirror(priv->mon, diskAlias, nbd_dest, - NULL, speed, 0, 0, mirror_flags); + "raw", speed, 0, 0, mirror_flags); if (qemuDomainObjExitMonitor(driver, vm) < 0 || mon_ret < 0) { qemuBlockJobSyncEnd(driver, vm, disk, NULL); -- 1.9.1