[Libguestfs] [PATCH for discussion only] launch: Add add_drive 'serial' option.

These two patches are for discussion of the proposed API only (in fact, it doesn't compile). virtio-scsi allows you to name drives (using the qemu serial=... option or libvirt <serial/>). Let's allow users to specify a serial when adding a drive, and then map that to a well-known name in the libguestfs API (/dev/disk/guests/SERIAL[PARTNUM]). Note that I chose not to change list-devices / list-partitions. These still return raw device names (which still exist, even if the serial is used). Instead there is a new API called list-serial-names which returns a mapping of the serial names to raw device names. This patch is in preparation for hotplugging. The plan would be to remove the restriction that add_drive{_opts} has to be called before launch. If it's called after launch (ie. hotplugging) then we strongly recommend that users specify the serial option so the disk has a predictable name. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/