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

[David Sterba <dsterba@suse.cz>]

On Thu, Jul 25, 2024 at 04:28:35PM -0700, Omar Sandoval wrote:
> 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))

This removes the last use of fd_converter

module.c:22:12: warning: ‘fd_converter’ defined but not used [-Wunused-function]
   22 | static int fd_converter(PyObject *o, void *p)

I'll ifdef it out as it will be probably needed in the future.