[PATCH 2/4] Python QEMU utils: introduce a generic feature list

[Cleber Rosa <crosa@redhat.com>]

Which can be used to check for any "feature" that is available as a
QEMU command line option, and that will return its list of available
options.

This is a generalization of the list_accel() utility function, which
is itself re-implemented in terms of the more generic feature.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
---
 python/qemu/utils/__init__.py |  2 ++
 python/qemu/utils/accel.py    | 15 ++----------
 python/qemu/utils/feature.py  | 44 +++++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 13 deletions(-)
 create mode 100644 python/qemu/utils/feature.py

diff --git a/python/qemu/utils/__init__.py b/python/qemu/utils/__init__.py
index 7f1a5138c4..1d0789eaa2 100644
--- a/python/qemu/utils/__init__.py
+++ b/python/qemu/utils/__init__.py
@@ -20,12 +20,14 @@
 
 # pylint: disable=import-error
 from .accel import kvm_available, list_accel, tcg_available
+from .feature import list_feature
 
 
 __all__ = (
     'get_info_usernet_hostfwd_port',
     'kvm_available',
     'list_accel',
+    'list_feature',
     'tcg_available',
 )
 
diff --git a/python/qemu/utils/accel.py b/python/qemu/utils/accel.py
index 297933df2a..b5bb80c6d3 100644
--- a/python/qemu/utils/accel.py
+++ b/python/qemu/utils/accel.py
@@ -14,13 +14,11 @@
 # the COPYING file in the top-level directory.
 #
 
-import logging
 import os
-import subprocess
 from typing import List, Optional
 
+from qemu.utils.feature import list_feature
 
-LOG = logging.getLogger(__name__)
 
 # Mapping host architecture to any additional architectures it can
 # support which often includes its 32 bit cousin.
@@ -39,16 +37,7 @@ def list_accel(qemu_bin: str) -> List[str]:
     @raise Exception: if failed to run `qemu -accel help`
     @return a list of accelerator names.
     """
-    if not qemu_bin:
-        return []
-    try:
-        out = subprocess.check_output([qemu_bin, '-accel', 'help'],
-                                      universal_newlines=True)
-    except:
-        LOG.debug("Failed to get the list of accelerators in %s", qemu_bin)
-        raise
-    # Skip the first line which is the header.
-    return [acc.strip() for acc in out.splitlines()[1:]]
+    return list_feature(qemu_bin, 'accel')
 
 
 def kvm_available(target_arch: Optional[str] = None,
diff --git a/python/qemu/utils/feature.py b/python/qemu/utils/feature.py
new file mode 100644
index 0000000000..b4a5f929ab
--- /dev/null
+++ b/python/qemu/utils/feature.py
@@ -0,0 +1,44 @@
+"""
+QEMU feature module:
+
+This module provides a utility for discovering the availability of
+generic features.
+"""
+# Copyright (C) 2022 Red Hat Inc.
+#
+# Authors:
+#  Cleber Rosa <crosa@redhat.com>
+#
+# This work is licensed under the terms of the GNU GPL, version 2.  See
+# the COPYING file in the top-level directory.
+#
+
+import logging
+import subprocess
+from typing import List
+
+
+LOG = logging.getLogger(__name__)
+
+
+def list_feature(qemu_bin: str, feature: str) -> List[str]:
+    """
+    List available options the QEMU binary for a given feature type.
+
+    By calling a "qemu $feature -help" and parsing its output.
+
+    @param qemu_bin (str): path to the QEMU binary.
+    @param feature (str): feature name, matching the command line option.
+    @raise Exception: if failed to run `qemu -feature help`
+    @return a list of available options for the given feature.
+    """
+    if not qemu_bin:
+        return []
+    try:
+        out = subprocess.check_output([qemu_bin, '-%s' % feature, 'help'],
+                                      universal_newlines=True)
+    except:
+        LOG.debug("Failed to get the list of %s(s) in %s", feature, qemu_bin)
+        raise
+    # Skip the first line which is the header.
+    return [item.split(' ', 1)[0] for item in out.splitlines()[1:]]
-- 
2.25.4