[qa] Work around QEMU bug in handling "-set" command-line option

Newer versions of QEMU (observed with QEMU 7.2.1 on Fedora 38) seem
not to be able to handle the "-set netdev.hostnet0.bootfile=..."
command-line option that we use to specify the per-test boot URL.  The
error message observed is:

  qemu-system-x86_64: ...: there is no netdev "hostnet0" defined

Adding debug prints to a test build of QEMU shows that at the point
that the "-set" option is handled, the list of netdevs is empty.  This
appears therefore to be a bug in the order of processing command-line
options.  The precise root cause has not been identified, since QEMU's
command-line parsing logic is fairly arcane and relies heavily on
autogenerated code fragments.

Work around the problem by creating a wrapper script that strips the
"-set netdev.hostnet0.bootfile=..." option and instead injects the
bootfile as part of the "-netdev" option found earlier in the same
command line.

(In an ideal world, libvirt would provide a clean way to specify the
bootfile or other options for a "user" network interface, but such a
mechanism does not seem to exist at present.)

Signed-off-by: Michael Brown <[email protected]>

test/qemu-system-x86_64

@@ -0,0 +1 @@
+qemu-wrapper

test/qemu-wrapper

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+#
+# Work around buggy parsing of "-set" option in newer versions of QEMU
+
+from itertools import pairwise
+import json
+import re
+import os
+import sys
+
+# Replace wrapper binary name
+#
+argv = sys.argv
+argv[0] = os.path.basename(argv[0])
+
+# Identify bootfile URL, if specified
+#
+bootfile = None
+bootfileidx = None
+for idx, (opt, val) in enumerate(pairwise(argv)):
+    # Look for "-set netdev.*.bootfile=..."
+    if opt == '-set':
+        m = re.fullmatch(r'netdev\..*\.bootfile=(?P<bootfile>.+)', val)
+        if m:
+            # Record bootfile and position within argument list
+            bootfile = m['bootfile']
+            bootfileidx = idx
+            break
+
+# Hack bootfile URL into argument list, if applicable
+#
+# We assume that only versions of QEMU that are sufficiently new to
+# handle JSON arguments will have the bug that prevents correct
+# parsing of the "-set" option.
+#
+if bootfile:
+    for idx, (opt, val) in enumerate(pairwise(argv)):
+        # Look for "-netdev {json argument}"
+        if opt == '-netdev':
+            try:
+                jval = json.loads(val)
+            except json.JSONDecodeError:
+                continue
+            # Add bootfile to JSON argument
+            jval['bootfile'] = bootfile
+            val = json.dumps(jval)
+            argv[idx + 1] = val
+            # Strip "-set netdev.*.bootfile=..." from argument list
+            argv[bootfileidx:(bootfileidx + 2)] = []
+            break
+
+# Execute real QEMU binary
+#
+os.execvp(argv[0], argv)

test/testwimboot

@@ -103,6 +103,8 @@ def vm_xml(virttype, name, uuid, memory, uefi, logfile, romfile, booturl):
     x_memory.text = str(memory)
     x_memory.attrib['unit'] = 'MiB'
     x_devices = etree.SubElement(x_domain, 'devices')
+    x_emulator = etree.SubElement(x_devices, 'emulator')
+    x_emulator.text = os.path.abspath('qemu-system-x86_64')
     x_graphics = etree.SubElement(x_devices, 'graphics')
     x_graphics.attrib['type'] = 'spice'
     x_video = etree.SubElement(x_devices, 'video')