Fix LVM device name for file backed disks, so snapshot can be created. Also only use the nouuid for xfs filesystems

virt-backup

@@ -64,6 +64,8 @@ $opts{compress} = 'none';
 $opts{lvcreate} = '/sbin/lvcreate -c 512';
 # lvremove path
 $opts{lvremove} = '/sbin/lvremove';
+# lvs path
+$opts{lvs} = '/sbin/lvs';
 # Override path to the LVM backend
 # Usefull if you have a layer between the filesystem
 # and the LVM volume, like GlusterFS
@@ -333,8 +335,13 @@ sub prepare_backup{
             # If the disk is a file
             elsif ($disk->{type} eq 'file'){
                 # Try to find the mount point, and the backing device
-                my @df = `df -P $source`;
+                my @df = `df -PT $source`;
-                my ($dev,undef,undef,undef,undef,$mount) = split /\s+/, $df[1];
+                my ($dev,$type,undef,undef,undef,undef,$mount) = split /\s+/, $df[1];
+                # Ok, we now have the backing device which probably looks like /dev/mapper/vg-lv
+                # We cannot pass this arg to lvcreate to take a snapshot, wee need to detect Volume Group
+                # name and Logical Volume name
+                my (undef,$lv,$vg) = split (/\s+/, `/sbin/lvs --noheadings -o lv_name,vg_name $dev </dev/null`);
+                $dev = '/dev/'. $vg . '/' . $lv
                 # The backing device can be detected, but can also be overwritten with --lvm=/dev/data/vm
                 # This can be usefull for example when you use GlusterFS. Df will return something like
                 # localhost:/vmstore as the device, but this GlusterFS volume might be backed by an LVM
@@ -361,7 +368,9 @@ sub prepare_backup{
                         my $snap = $lvm.$time;
                         mkdir $mp || die "Couldn't create $mp: $!";
                         # -o nouuid is needed if XFS is used
-                        system("/bin/mount -o nouuid $snap $mp");
+                        my $option = ($type eq 'xfs') ? '-o nouuid': '';
+                        print "Mounting $snap on $mp\n (as an $type filesystem)\n" if ($opts{debug});
+                        system("/bin/mount $option $snap $mp");
                         open MOUNT, ">$backupdir.meta/mount";
                         print MOUNT $lvm;
                         close MOUNT;