kpartx_plugin: create new loop device if required

Fix a kpartx plugin failure when no free loop devices are available: in
this scenario, the `kpartx -asv` command can fail. To resolve this,
`losetup -f --show <image-file>` is now executed first, which will to
create a new loop device if required, before mapping the partitions
using `kpartx`.

1 files changed, 7 insertions, 1 deletions

diff --git a/vmdb/plugins/kpartx_plugin.py b/vmdb/plugins/kpartx_plugin.py
index 36cf42f..baa4f54 100644
--- a/vmdb/plugins/kpartx_plugin.py
+++ b/vmdb/plugins/kpartx_plugin.py
@@ -39,7 +39,13 @@ class KpartxStepRunner(vmdb.StepRunnerInterface):
             state.tags.set_dev(tag, dev)
 
     def kpartx(self, device):
-        output = vmdb.runcmd(["kpartx", "-asv", device]).decode("UTF-8")
+        # Allocate the loop device first -- creating one if required -- before
+        # mapping the partitions usign kpartx. This handles scenarios where no
+        # free loop devices are available.
+        loop_device = (
+            vmdb.runcmd(["losetup", "-f", "--show", device]).decode("UTF-8").strip()
+        )
+        output = vmdb.runcmd(["kpartx", "-usv", loop_device]).decode("UTF-8")
         for line in output.splitlines():
             words = line.split()
             if words[0] == "add":