docs: sphinx/kfigure.py: Delegate inkscape msg to kernellog.verbose

Depending on its version, distro config, and system-setup type,
inkscape(1) emits various warning messages which are harmless in
command-line uses.

List of such warning messages (incomplete, long ones wrapped):

  - Gtk-Message: hh:mm:ss.nnn: Failed to load module "canberra-gtk-module"
  - Unable to init server: Could not connect: Connection refused
  - Failed to get connection
  - ** (inkscape:xxx): CRITICAL **: hh:mm:ss.nnn: dbus_g_proxy_new_for_name:
    assertion 'connection != NULL' failed
  - ** (inkscape:xxx): CRITICAL **: hh:mm:ss.nnn: dbus_g_proxy_call:
    assertion 'DBUS_IS_G_PROXY (proxy)' failed
  - ** (inkscape:xxx): CRITICAL **: hh:mm:ss.nnn: dbus_g_connection_register_g_object:
    assertion 'connection != NULL' failed
  - ** (inkscape:xxx): WARNING **: hh:mm:ss.nnn:
    Fonts dir '/usr/share/inkscape/fonts' does not exist and will be ignored.

To avoid unnecessary anxiety, capture the message and output it via
kernellog.verbose or kernellog.warn depending on the exit code.
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/e26a7b53-9155-8394-4a31-6006379b65a5@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx/kfigure.py

@@ -200,7 +200,8 @@ def setupTools(app):
                        "graphviz from https://www.graphviz.org")
     if inkscape_cmd:
         kernellog.verbose(app, "use inkscape(1) from: " + inkscape_cmd)
-        inkscape_ver = subprocess.check_output([inkscape_cmd, '--version'])
+        inkscape_ver = subprocess.check_output([inkscape_cmd, '--version'],
+                                               stderr=subprocess.DEVNULL)
         ver_one_ptn = b'Inkscape 1'
         inkscape_ver_one = re.search(ver_one_ptn, inkscape_ver)
         convert_cmd = None
@@ -373,17 +374,32 @@ def svg2pdf(app, svg_fname, pdf_fname):
 
     """
     cmd = [convert_cmd, svg_fname, pdf_fname]
+    cmd_name = 'convert(1)'
 
     if inkscape_cmd:
+        cmd_name = 'inkscape(1)'
         if inkscape_ver_one:
             cmd = [inkscape_cmd, '-o', pdf_fname, svg_fname]
         else:
             cmd = [inkscape_cmd, '-z', '--export-pdf=%s' % pdf_fname, svg_fname]
 
-    # use stdout and stderr from parent
-    exit_code = subprocess.call(cmd)
+    try:
+        warning_msg = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
+        exit_code = 0
+    except subprocess.CalledProcessError as err:
+        warning_msg = err.output
+        exit_code = err.returncode
+        pass
+
     if exit_code != 0:
         kernellog.warn(app, "Error #%d when calling: %s" % (exit_code, " ".join(cmd)))
+        if warning_msg:
+            kernellog.warn(app, "Warning msg from %s: %s"
+                           % (cmd_name, str(warning_msg, 'utf-8')))
+    elif warning_msg:
+        kernellog.verbose(app, "Warning msg from %s (likely harmless):\n%s"
+                          % (cmd_name, str(warning_msg, 'utf-8')))
+
     return bool(exit_code == 0)
 
 def svg2pdf_by_rsvg(app, svg_fname, pdf_fname):