feat(instances): a new VM can get a cloud-init seed with its hostname and SSH keys

Cloud images read their first-boot settings with cloud-init. The panel
served them only over HTTP, which a VM reaches only with the network
and a reverse DNS name for its address. A new VM can now carry them
itself: Cloud-init seed (Advanced) on the create form, or cloud_init in
the API.

The job writes a NoCloud seed, an ISO labelled cidata, into the disk's
directory pool as cidata-<uuid>.iso and puts it in the VM's CD-ROM
drive. Its meta-data holds the VM's UUID as instance-id and its name as
hostname, written as JSON so a VM named 123 or yes keeps a string
hostname; its user-data is what the HTTP datasource serves, with the
creating user's SSH keys. The ISO is built with pycdlib and written
through a libvirt stream, as the NVRAM copy is, now one helper for both.

A seed needs a CD-ROM bus and a directory pool, else the create is
refused. A failed create deletes the seed with the new disk, recovery
names one left behind, and deleting the VM with its disks deletes its
seed, found in the pools by name even when ejected. A clone's drive is
left empty: the seed is the source VM's identity.

vrtManager/instance.py

@@ -1,6 +1,5 @@
 import base64
 import contextlib
-import io
 import ipaddress
 import json
 import logging
@@ -200,20 +199,7 @@ class wvmInstances(wvmConnect):
             vol.download(stream, 0, 0, 0)
             stream.recvAll(lambda _stream, data, out: out.append(data), chunks)
             stream.finish()
-            data = b"".join(chunks)
-            copy = target.createXML(
-                f"<volume><name>{util.xml_escape(name)}</name><capacity>{len(data)}</capacity>"
-                "<target><format type='raw'/></target></volume>",
-                0,
-            )
-            try:
-                stream = self.wvm.newStream(0)
-                copy.upload(stream, 0, len(data), 0)
-                stream.sendAll(lambda _stream, size, buffer: buffer.read(size), io.BytesIO(data))
-                stream.finish()
-            except Exception:
-                copy.delete(0)
-                raise
+            self.upload_volume(target, name, b"".join(chunks))
         return name
 
     def delete_nvram(self, name):
@@ -1525,10 +1511,14 @@ class wvmInstance(wvmConnect):
     def split_disk_paths_by_use(self):
         """This VM's disk paths, split into (only this VM, also used by another
         domain). With external snapshots, the files below a disk that the
-        snapshots were taken on, and their memory files, are the VM's too."""
+        snapshots were taken on, and their memory files, are the VM's too, and
+        so is its cloud-init seed, in a CD-ROM drive or ejected."""
         self.refresh_instance_pools()
         own = [disk["path"] for disk in self.get_disk_devices() if disk["path"]]
         own += self._snapshot_chain_files(own)
+        seed = self._seed_path()
+        if seed:
+            own.append(seed)
         used_elsewhere = self.paths_used_by_other_domains(own)
         # a kept file keeps the files below it
         for path in [path for path in own if path in used_elsewhere]:
@@ -1539,6 +1529,15 @@ class wvmInstance(wvmConnect):
             [path for path in own if path in used_elsewhere],
         )
 
+    def _seed_path(self):
+        """The path of this VM's cloud-init seed (cidata-<uuid>.iso) in an active pool, or None."""
+        name = f"cidata-{self.get_uuid()}.iso"
+        for pool in self.wvm.listAllStoragePools(VIR_CONNECT_LIST_STORAGE_POOLS_ACTIVE):
+            vol = self._find_volume(pool, name)
+            if vol is not None:
+                return vol.path()
+        return None
+
     def _snapshot_chain_files(self, tops):
         """The files of this VM's external snapshots that these disk images
         grow from or that grow from them: the backing files snapshots were
@@ -1974,6 +1973,11 @@ class wvmInstance(wvmConnect):
             raise ValueError("An instance with the clone name already exists")
 
         tree = etree.fromstring(self._XMLDesc(PERSISTENT_XML))
+        # the cloud-init seed holds the VM's own instance-id and hostname: the clone's drive stays empty
+        seed = f"cidata-{tree.findtext('uuid')}.iso"
+        for source in tree.xpath("devices/disk[@device='cdrom']/source"):
+            if os.path.basename(source.get("file") or "") == seed:
+                source.getparent().remove(source)
         tree.find("name").text = clone_data["name"]
         uuid_el = tree.find("uuid")
         if uuid_el is None: