[libvirt] [PATCH] qemu: snapshot: Forbid snapshots when backing is a scsi passthrough disk

[Peter Krempa]

https://bugzilla.redhat.com/show_bug.cgi?id=1034993

SCSI passthrough disks (<disk .. device="lun">) can't be used as backing
for snapshots. Currently with upstream qemu the vm crashes on such
attempt.

This patch adds a early check to catch an attempt to do such a snapshot
and rejects it right away. qemu will fix the issue but this will let us
control the error message.
---

Notes:
    You need a domain with a similar disk config to test this patch:
        <disk type='block' device='lun'>
          <driver name='qemu' type='raw'/>
          <source dev='/dev/disk/by-path/ip-192.168.122.223:3260-iscsi-iqn.2011-03.org.example.istgt:test-lun-0'/>
          <target dev='sda' bus='scsi'/>
          <address type='drive' controller='0' bus='0' target='0' unit='0'/>
        </disk>
        <controller type='scsi' index='0' model='virtio-scsi'>
          <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
        </controller>

 src/qemu/qemu_driver.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index b101d77..bc29714 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -12206,7 +12206,7 @@ endjob:
 }

 static int
-qemuDomainSnapshotPrepareDiskExternalBacking(virDomainDiskDefPtr disk)
+qemuDomainSnapshotPrepareDiskExternalBackingInactive(virDomainDiskDefPtr disk)
 {
     int actualType = qemuDiskGetActualType(disk);

@@ -12250,6 +12250,23 @@ qemuDomainSnapshotPrepareDiskExternalBacking(virDomainDiskDefPtr disk)


 static int
+qemuDomainSnapshotPrepareDiskExternalBackingActive(virDomainDiskDefPtr disk)
+{
+    int actualType = qemuDiskGetActualType(disk);
+
+    if (actualType == VIR_DOMAIN_DISK_TYPE_BLOCK &&
+        disk->device == VIR_DOMAIN_DISK_DEVICE_LUN) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("external active snapshots are not supported on scsi "
+                         "passthrough devices"));
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
 qemuDomainSnapshotPrepareDiskExternalOverlayActive(virDomainSnapshotDiskDefPtr disk)
 {
     int actualType = qemuSnapshotDiskGetActualType(disk);
@@ -12315,12 +12332,15 @@ qemuDomainSnapshotPrepareDiskExternal(virConnectPtr conn,
         if (qemuTranslateDiskSourcePool(conn, disk) < 0)
             return -1;

-        if (qemuDomainSnapshotPrepareDiskExternalBacking(disk) < 0)
+        if (qemuDomainSnapshotPrepareDiskExternalBackingInactive(disk) < 0)
             return -1;

         if (qemuDomainSnapshotPrepareDiskExternalOverlayInactive(snapdisk) < 0)
             return -1;
     } else {
+        if (qemuDomainSnapshotPrepareDiskExternalBackingActive(disk) < 0)
+            return -1;
+
         if (qemuDomainSnapshotPrepareDiskExternalOverlayActive(snapdisk) < 0)
             return -1;
     }
-- 
1.8.5.3