Re: [libvirt] [PATCH]: Export the 'label' on block devices

To support LVM partitioning in oVirt, one of the things we need is the ability to tell what kind of label is currently on a block device. Here, a 'label' is used in the same sense that it is used in parted; namely, it defines which kind of partition table is on the disk, whether it be DOS, LVM2, SUN, BSD, etc. Note that this is different than the partition type; those are things like Linux, FAT16, FAT32, etc. This actually turns out to be fairly easy to implement; there are really only a few labels that are in common use, and they all have an easy signature to recognize (but see comments in the code about pc98). This patch implements label detection on block devices in virStorageBackendUpdateVolInfoFD, and hooks it up to the iSCSI backend so it works there. To keep code duplication down, I moved some of the enum's from storage_backend_disk.c into a common place. Note, however, that there is a slight semantic change because of this. Previously, if no label was found on a disk in storage_backend_disk.c, it would always return "dos" as the label type. That's not actually true, though; if it's a completely zeroed disk, for instance, it really just has label type of 'unknown'. This patch changes to the new semantic of 'unknown' for label types we don't understand. I don't think this will be a huge issue for compatibility, but there could be something I'm missing. Otherwise, this patch has been tested by me to work, and now when you do: