[PATCH] libbtrfsutil: python: fix build on Python 3.13

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

Python 3.13, currently in beta, removed the internal
_PyObject_LookupSpecial function. The libbtrfsutil Python bindings use
it in the path_converter() function because it was based on internal
path_converter() function in CPython [1]. This is causing build failures
on Fedora Rawhide [2] and Gentoo [3]. Replace path_converter() with a
version that only uses public functions based on the one in drgn [4].

1: https://github.com/python/cpython/blob/d9efa45d7457b0dfea467bb1c2d22c69056ffc73/Modules/posixmodule.c#L1253
2: https://bugzilla.redhat.com/show_bug.cgi?id=2245650
3: https://github.com/kdave/btrfs-progs/issues/838
4: https://github.com/osandov/drgn/blob/9ad29fd86499eb32847473e928b6540872d3d59a/libdrgn/python/util.c#L81

Reported-by: Neal Gompa <neal@gompa.dev>
Reported-by: Sam James <sam@gentoo.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 libbtrfsutil/python/btrfsutilpy.h |  7 +--
 libbtrfsutil/python/module.c      | 98 ++++++++++---------------------
 2 files changed, 33 insertions(+), 72 deletions(-)

diff --git a/libbtrfsutil/python/btrfsutilpy.h b/libbtrfsutil/python/btrfsutilpy.h
index ee70c23a..49702dcc 100644
--- a/libbtrfsutil/python/btrfsutilpy.h
+++ b/libbtrfsutil/python/btrfsutilpy.h
@@ -40,16 +40,13 @@ extern PyTypeObject SubvolumeInfo_type;
 extern PyTypeObject SubvolumeIterator_type;
 extern PyTypeObject QgroupInherit_type;
 
-/*
- * Helpers for path arguments based on posixmodule.c in CPython.
- */
 struct path_arg {
 	bool allow_fd;
-	char *path;
 	int fd;
+	char *path;
 	Py_ssize_t length;
 	PyObject *object;
-	PyObject *cleanup;
+	PyObject *bytes;
 };
 int path_converter(PyObject *o, void *p);
 void path_cleanup(struct path_arg *path);
diff --git a/libbtrfsutil/python/module.c b/libbtrfsutil/python/module.c
index 2657ee28..9b0b86b5 100644
--- a/libbtrfsutil/python/module.c
+++ b/libbtrfsutil/python/module.c
@@ -44,85 +44,49 @@ static int fd_converter(PyObject *o, void *p)
 int path_converter(PyObject *o, void *p)
 {
 	struct path_arg *path = p;
-	int is_index, is_bytes, is_unicode;
-	PyObject *bytes = NULL;
-	Py_ssize_t length = 0;
-	char *tmp;
 
 	if (o == NULL) {
 		path_cleanup(p);
 		return 1;
 	}
 
-	path->object = path->cleanup = NULL;
-	Py_INCREF(o);
-
 	path->fd = -1;
+	path->path = NULL;
+	path->length = 0;
+	path->bytes = NULL;
+	if (path->allow_fd && PyIndex_Check(o)) {
+		PyObject *fd_obj;
+		int overflow;
+		long fd;
 
-	is_index = path->allow_fd && PyIndex_Check(o);
-	is_bytes = PyBytes_Check(o);
-	is_unicode = PyUnicode_Check(o);
-
-	if (!is_index && !is_bytes && !is_unicode) {
-		_Py_IDENTIFIER(__fspath__);
-		PyObject *func;
-
-		func = _PyObject_LookupSpecial(o, &PyId___fspath__);
-		if (func == NULL)
-			goto err_format;
-		Py_DECREF(o);
-		o = PyObject_CallFunctionObjArgs(func, NULL);
-		Py_DECREF(func);
-		if (o == NULL)
+		fd_obj = PyNumber_Index(o);
+		if (!fd_obj)
 			return 0;
-		is_bytes = PyBytes_Check(o);
-		is_unicode = PyUnicode_Check(o);
-	}
-
-	if (is_unicode) {
-		if (!PyUnicode_FSConverter(o, &bytes))
-			goto err;
-	} else if (is_bytes) {
-		bytes = o;
-		Py_INCREF(bytes);
-	} else if (is_index) {
-		if (!fd_converter(o, &path->fd))
-			goto err;
-		path->path = NULL;
-		goto out;
+		fd = PyLong_AsLongAndOverflow(fd_obj, &overflow);
+		Py_DECREF(fd_obj);
+		if (fd == -1 && PyErr_Occurred())
+			return 0;
+		if (overflow > 0 || fd > INT_MAX) {
+			PyErr_SetString(PyExc_OverflowError,
+					"fd is greater than maximum");
+			return 0;
+		}
+		if (fd < 0) {
+			PyErr_SetString(PyExc_ValueError, "fd is negative");
+			return 0;
+		}
+		path->fd = fd;
 	} else {
-err_format:
-		PyErr_Format(PyExc_TypeError, "expected %s, not %s",
-			     path->allow_fd ? "string, bytes, os.PathLike, or integer" :
-			     "string, bytes, or os.PathLike",
-			     Py_TYPE(o)->tp_name);
-		goto err;
+		if (!PyUnicode_FSConverter(o, &path->bytes)) {
+			path->object = path->bytes = NULL;
+			return 0;
+		}
+		path->path = PyBytes_AS_STRING(path->bytes);
+		path->length = PyBytes_GET_SIZE(path->bytes);
 	}
-
-	length = PyBytes_GET_SIZE(bytes);
-	tmp = PyBytes_AS_STRING(bytes);
-	if ((size_t)length != strlen(tmp)) {
-		PyErr_SetString(PyExc_TypeError,
-				"path has embedded nul character");
-		goto err;
-	}
-
-	path->path = tmp;
-	if (bytes == o)
-		Py_DECREF(bytes);
-	else
-		path->cleanup = bytes;
-	path->fd = -1;
-
-out:
-	path->length = length;
+	Py_INCREF(o);
 	path->object = o;
 	return Py_CLEANUP_SUPPORTED;
-
-err:
-	Py_XDECREF(o);
-	Py_XDECREF(bytes);
-	return 0;
 }
 
 PyObject *list_from_uint64_array(const uint64_t *arr, size_t n)
@@ -150,8 +114,8 @@ PyObject *list_from_uint64_array(const uint64_t *arr, size_t n)
 
 void path_cleanup(struct path_arg *path)
 {
+	Py_CLEAR(path->bytes);
 	Py_CLEAR(path->object);
-	Py_CLEAR(path->cleanup);
 }
 
 static PyMethodDef btrfsutil_methods[] = {
-- 
2.45.2