[Libguestfs] [libnbd PATCH] python: Fix bindings for Path parameters

[Eric Blake]

Our use of PyUnicode_FSConverter was wrong - the result is a PyObject*
rather than a char* (where dereferencing then calling free() on that
pointer as char* has catastrophic effects).

With this patch, I was able to set up a qemu-nbd encrypted server over
a Unix socket (using a pending patch on the qemu list), coupled with
a python connection to that socket:

$ ~/qemu/qemu-nbd -r -k /tmp/nbdsock --object \
  tls-creds-psk,id=tls0,endpoint=server,dir=/home/eblake/libnbd/tests \
  --tls-creds tls0 -f raw -x / tmpfile
$ ./run nbdsh
nbd> h.set_tls_psk_file('tests/keys.psk')
nbd> h.set_tls(2)
nbd> h.set_export_name('/')
nbd> h.connect_unix('/tmp/nbdsock')

instead of getting a segfault.
---
 generator/generator | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/generator/generator b/generator/generator
index c29460c..fa12232 100755
--- a/generator/generator
+++ b/generator/generator
@@ -3608,7 +3608,9 @@ let print_python_binding name { args; ret } =
     | Mutable arg ->
        pr "  PyObject *%s;\n" (List.hd (name_of_arg arg))
     | Opaque _ -> ()
-    | Path n -> pr "  char *%s = NULL;\n" n
+    | Path n ->
+       pr "  PyObject *py_%s = NULL;\n" n;
+       pr "  char *%s = NULL;\n" n
     | SockAddrAndLen (n, _) ->
        pr "  /* XXX Complicated - Python uses a tuple of different\n";
        pr "   * lengths for the different socket types.\n";
@@ -3699,7 +3701,7 @@ let print_python_binding name { args; ret } =
     | Int64 n -> pr ", &%s" n
     | Mutable arg -> pr ", &%s" (List.hd (name_of_arg arg))
     | Opaque n -> pr ", &%s_data->data" (find_callback n)
-    | Path n -> pr ", PyUnicode_FSConverter, &%s" n
+    | Path n -> pr ", PyUnicode_FSConverter, &py_%s" n
     | SockAddrAndLen (n, _) -> pr ", &%s" n
     | String n -> pr ", &%s" n
     | StringList n -> pr ", &py_%s" n
@@ -3750,7 +3752,9 @@ let print_python_binding name { args; ret } =
     | Mutable _ ->
        pr "  abort (); /* Mutable for normal Python parameters not impl */\n"
     | Opaque n -> ()
-    | Path _ -> ()
+    | Path n ->
+       pr "  %s = PyBytes_AS_STRING (py_%s);\n" n n;
+       pr "  assert (%s != NULL);\n" n
     | SockAddrAndLen _ ->
        pr "  abort (); /* XXX SockAddrAndLen not implemented */\n";
     | String _ -> ()
@@ -3860,7 +3864,8 @@ let print_python_binding name { args; ret } =
     | Int64 _ -> ()
     | Mutable _ -> ()
     | Opaque _ -> ()
-    | Path n -> pr "  free (%s);\n" n
+    | Path n ->
+       pr "  Py_XDECREF (py_%s);\n" n
     | SockAddrAndLen _ -> ()
     | String n -> ()
     | StringList n -> pr "  nbd_internal_py_free_string_list (%s);\n" n
-- 
2.20.1