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pygrub/fsimage: make it work with python 3
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With the help of two porting guides and cpython source code:

1. Use PyBytes to replace PyString counterparts.
2. Use PyVarObject_HEAD_INIT.
3. Remove usage of Py_FindMethod.
4. Use new module initialisation routine.

For xen-project#3, Py_FindMethod was removed, yet an alternative wasn't
documented.  The code is the result of reverse-engineering cpython
commit 6116d4a1d1

https://docs.python.org/3/howto/cporting.html
http://python3porting.com/cextensions.html

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Wei Liu authored and Eric Chanudet committed May 4, 2021
1 parent 2fb694e commit ca26070
Showing 1 changed file with 69 additions and 54 deletions.
123 changes: 69 additions & 54 deletions tools/pygrub/src/fsimage/fsimage.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,12 +26,6 @@
#include <xenfsimage.h>
#include <stdlib.h>

#if (PYTHON_API_VERSION >= 1011)
#define PY_PAD 0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L,0L
#else
#define PY_PAD 0L,0L,0L,0L
#endif

typedef struct fsimage_fs {
PyObject_HEAD
fsi_t *fs;
Expand Down Expand Up @@ -66,12 +60,24 @@ fsimage_file_read(fsimage_file_t *file, PyObject *args, PyObject *kwargs)

bufsize = size ? size : 4096;

if ((buffer = PyString_FromStringAndSize(NULL, bufsize)) == NULL)
buffer =
#if PY_MAJOR_VERSION < 3
PyString_FromStringAndSize(NULL, bufsize);
#else
PyBytes_FromStringAndSize(NULL, bufsize);
#endif

if (buffer == NULL)
return (NULL);

while (1) {
int err;
void *buf = PyString_AS_STRING(buffer) + bytesread;
void *buf =
#if PY_MAJOR_VERSION < 3
PyString_AS_STRING(buffer) + bytesread;
#else
PyBytes_AS_STRING(buffer) + bytesread;
#endif

err = fsi_pread_file(file->file, buf, bufsize,
bytesread + offset);
Expand All @@ -91,12 +97,20 @@ fsimage_file_read(fsimage_file_t *file, PyObject *args, PyObject *kwargs)
if (bufsize == 0)
break;
} else {
#if PY_MAJOR_VERSION < 3
if (_PyString_Resize(&buffer, bytesread + bufsize) < 0)
#else
if (_PyBytes_Resize(&buffer, bytesread + bufsize) < 0)
#endif
return (NULL);
}
}

#if PY_MAJOR_VERSION < 3
_PyString_Resize(&buffer, bytesread);
#else
_PyBytes_Resize(&buffer, bytesread);
#endif
return (buffer);
}

Expand All @@ -113,11 +127,13 @@ static struct PyMethodDef fsimage_file_methods[] = {
{ NULL, NULL, 0, NULL }
};

#if PY_MAJOR_VERSION < 3
static PyObject *
fsimage_file_getattr(fsimage_file_t *file, char *name)
{
return (Py_FindMethod(fsimage_file_methods, (PyObject *)file, name));
}
#endif

static void
fsimage_file_dealloc(fsimage_file_t *file)
Expand All @@ -130,29 +146,18 @@ fsimage_file_dealloc(fsimage_file_t *file)

static char fsimage_file_type__doc__[] = "Filesystem image file";
PyTypeObject fsimage_file_type = {
PyObject_HEAD_INIT(&PyType_Type)
0, /* ob_size */
"xenfsimage.file", /* tp_name */
sizeof(fsimage_file_t), /* tp_size */
0, /* tp_itemsize */
(destructor) fsimage_file_dealloc, /* tp_dealloc */
0, /* tp_print */
(getattrfunc) fsimage_file_getattr, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_compare */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT, /* tp_flags */
fsimage_file_type__doc__,
PY_PAD
PyVarObject_HEAD_INIT(&PyType_Type, 0)
.tp_name = "xenfsimage.file",
.tp_basicsize = sizeof(fsimage_file_t),
.tp_dealloc = (destructor) fsimage_file_dealloc,
#if PY_MAJOR_VERSION < 3
.tp_getattr = (getattrfunc) fsimage_file_getattr,
#endif
.tp_flags = Py_TPFLAGS_DEFAULT,
.tp_doc = fsimage_file_type__doc__,
#if PY_MAJOR_VERSION >= 3
.tp_methods = fsimage_file_methods,
#endif
};

static PyObject *
Expand Down Expand Up @@ -215,11 +220,13 @@ static struct PyMethodDef fsimage_fs_methods[] = {
{ NULL, NULL, 0, NULL }
};

#if PY_MAJOR_VERSION < 3
static PyObject *
fsimage_fs_getattr(fsimage_fs_t *fs, char *name)
{
return (Py_FindMethod(fsimage_fs_methods, (PyObject *)fs, name));
}
#endif

static void
fsimage_fs_dealloc (fsimage_fs_t *fs)
Expand All @@ -232,29 +239,18 @@ fsimage_fs_dealloc (fsimage_fs_t *fs)
PyDoc_STRVAR(fsimage_fs_type__doc__, "Filesystem image");

PyTypeObject fsimage_fs_type = {
PyObject_HEAD_INIT(&PyType_Type)
0, /* ob_size */
"xenfsimage.fs", /* tp_name */
sizeof(fsimage_fs_t), /* tp_size */
0, /* tp_itemsize */
(destructor) fsimage_fs_dealloc, /* tp_dealloc */
0, /* tp_print */
(getattrfunc) fsimage_fs_getattr, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_compare */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT, /* tp_flags */
fsimage_fs_type__doc__,
PY_PAD
PyVarObject_HEAD_INIT(&PyType_Type, 0)
.tp_name = "xenfsimage.fs",
.tp_basicsize = sizeof(fsimage_fs_t),
.tp_dealloc = (destructor) fsimage_fs_dealloc,
#if PY_MAJOR_VERSION < 3
.tp_getattr = (getattrfunc) fsimage_fs_getattr,
#endif
.tp_flags = Py_TPFLAGS_DEFAULT,
.tp_doc = fsimage_fs_type__doc__,
#if PY_MAJOR_VERSION >= 3
.tp_methods = fsimage_fs_methods,
#endif
};

static PyObject *
Expand Down Expand Up @@ -316,8 +312,27 @@ static struct PyMethodDef fsimage_module_methods[] = {
{ NULL, NULL, 0, NULL }
};

#if PY_MAJOR_VERSION >= 3
static struct PyModuleDef fsimage_module_def = {
PyModuleDef_HEAD_INIT,
.m_name = "xenfsimage",
.m_size = -1,
.m_methods = fsimage_module_methods,
};
#endif

PyMODINIT_FUNC
#if PY_MAJOR_VERSION >= 3
PyInit_xenfsimage(void)
#else
initxenfsimage(void)
#endif
{
#if PY_MAJOR_VERSION < 3
Py_InitModule("xenfsimage", fsimage_module_methods);
#else
if (PyType_Ready(&fsimage_fs_type) < 0 || PyType_Ready(&fsimage_file_type) < 0)
return NULL;
return PyModule_Create(&fsimage_module_def);
#endif
}

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