Do not try to use zRAM devices for anything

These devices are mapped into memory, but nonetheless can appear
in lsblk output. Ignore them explicitly.

Change-Id: I2bb595ef29abdc98bd887bdf41c3c7f64cc3a7e6

ironic_python_agent/hardware.py

@@ -305,6 +305,12 @@ def list_all_block_devices(block_type='disk',
             raise errors.BlockDeviceError(
                 '%s must be returned by lsblk.' % ', '.join(sorted(missing)))
 
+        # NOTE(dtantsur): zRAM devices can appear in the output of lsblk, but
+        # we cannot do anything useful with them.
+        if device['KNAME'].startswith('zram'):
+            LOG.debug('Skipping zRAM device %s', device)
+            continue
+
         name = os.path.join('/dev', device['KNAME'])
 
         try:

ironic_python_agent/tests/unit/test_hardware.py

@@ -137,7 +137,8 @@ BLK_DEVICE_TEMPLATE = (
     ' ROTA="0" TYPE="disk"\n'
     'KNAME="sdd" MODEL="NWD-BLP4-1600   " SIZE="1765517033472" '
     ' ROTA="0" TYPE="disk"\n'
-    'KNAME="loop0" MODEL="" SIZE="109109248" ROTA="1" TYPE="loop"'
+    'KNAME="loop0" MODEL="" SIZE="109109248" ROTA="1" TYPE="loop"\n'
+    'KNAME="zram0" MODEL="" SIZE="" ROTA="0" TYPE="disk"'
 )
 
 # NOTE(pas-ha) largest device is 1 byte smaller than 4GiB

releasenotes/notes/no-zram-78cc6583f4f90a9c.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    No longer tries to use zRAM devices for anything.