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diff --git a/pytalloc_guide.txt b/pytalloc_guide.txt new file mode 100644 index 0000000..bd2b68c --- /dev/null +++ b/pytalloc_guide.txt @@ -0,0 +1,252 @@ +Using talloc in Samba4 +====================== + +.. contents:: + +Jelmer Vernooij +August 2013 + +The most current version of this document is available at + http://samba.org/ftp/unpacked/talloc/pytalloc_guide.txt + +pytalloc is a small library that provides glue for wrapping +talloc-allocated objects from C in Python objects. + +What is pytalloc, and what is it not? +------------------------------------- + +pytalloc is merely a helper library - it provides a convenient base type object +for objects that wrap talloc-maintained memory in C. It won't write your +bindings for you but it will make it easier to write C bindings that involve +talloc, and take away some of the boiler plate. + +Python 3 +-------- + +pytalloc can be used with Python 3. Usage from Python extension remains +the same, but for the C utilities, the library to link to is tagged with +Python's PEP3149 ABI tag, for example "pytalloc.cpython34m". +To make a build for Python 3, configure with PYTHON=/usr/bin/python3. +. +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +pytalloc_Object / pytalloc_BaseObject + +This is the new base class that all Python objects that wrap talloc pointers +derive from. It is itself a subclass of the "Object" type that all objects +in Python derive from. + +Note that you will almost never create objects of the pytalloc_Object type +itself, as they are just opaque pointers that can not be accessed from +Python. A common pattern is other objects that subclass pytalloc_Object and +rely on it for their memory management. + +Each `pytalloc_Object` wraps two core of information - a talloc context +and a pointer. The pointer is the actual data that is wrapped. The talloc +context is used for memory management purposes only; when the wrapping Python object +goes away, it unlinks the talloc context. The talloc context pointer and the ptr +can (and often do) have the same value. + +Each pytalloc_Object has a custom __repr__ implementation that +describes that it is a talloc object and the location of the +pointer it is wrapping. it also has a custom __cmp__/__eq__/__neq__ method that +compares the pointers the object is wrapping rather than the objects +themselves (since there can be multiple objects that wrap the same talloc +pointer). + +It is preferred to use pytalloc_BaseObject as this implementation +exposes less in the C ABI and correctly supports pointers in C arrays +in the way needed by PIDL. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyTypeObject *pytalloc_GetObjectType(void) + +Obtain a pointer to the PyTypeObject for `pytalloc_Object`. The +reference counter for the object will be NOT incremented, so the +caller MUST NOT decrement it when it no longer needs it (eg by using +`Py_DECREF`). + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyTypeObject *pytalloc_GetBaseObjectType(void) + +Obtain a pointer to the PyTypeObject for `pytalloc_BaseObject`. The +reference counter for the object will be NOT incremented, so the +caller MUST NOT decrement it when it no longer needs it (eg by using +`Py_DECREF`). + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +int pytalloc_BaseObject_PyType_Ready(PyTypeObject *type); + +Wrapper for PyType_Ready() that will set the correct values into +the PyTypeObject to create a BaseObject + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=- +int pytalloc_Check(PyObject *) + +Check whether a specific object is a talloc Object. Returns non-zero if it is +a pytalloc_Object and zero otherwise. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=- +int pytalloc_BaseObject_Check(PyObject *) + +Check whether a specific object is a talloc BaseObject. Returns non-zero if it is +a pytalloc_BaseObject and zero otherwise. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +int pytalloc_check_type(PyObject *py_obj, type) + +Check if the object based on `pytalloc_*Object` py_obj. type should be a +C type, similar to a type passed to `talloc_get_type`. +This can be used as a check before using pytalloc_get_type() +or an alternative codepath. Returns non-zero if it is +an object of the expected type and zero otherwise. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +type *pytalloc_get_type(PyObject *py_obj, type) + +Retrieve the pointer from a `pytalloc_Object` py_obj. type should be a +C type, similar to a type passed to `talloc_get_type`. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +pytalloc_get_ptr(PyObject *py_obj) + +Retrieve the pointer from a `pytalloc_Object` or `pytalloc_BaseObject` +py_obj. There is no type checking - use `pytalloc_get_type` if +possible. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +TALLOC_CTX *pytalloc_get_mem_ctx(PyObject *py_obj) + +Retrieve the talloc context associated with a pytalloc_Object or pytalloc_BaseObject. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_steal_ex(PyTypeObject *py_type, TALLOC_CTX *mem_ctx, void *ptr) + +Create a new Python wrapping object for a talloc pointer and context, with +py_type as associated Python sub type object. This typically used +when `mem_ctx` and `ptr` differ, e.g. a pointer to an array element. +`pytalloc_get_ptr()` can be used to get the pointer out of the object again. + +This will *not* increment the reference counter for the talloc context, +so the caller should make sure such an increment has happened. When the Python +object goes away, it will unreference the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_steal(PyTypeObject *py_type, void *ptr) + +Create a new Python wrapping object for a talloc pointer and context, with +py_type as associated Python sub type object. The pointer will also be used +as the talloc context. `pytalloc_get_type()` can be used to get +the pointer out of the object again. + +This will *not* increment the reference counter for the talloc context, +so the caller should make sure such an increment has happened. When the Python +object goes away, it will unreference the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_reference_ex(PyTypeObject *py_type, TALLOC_CTX *mem_ctx, void *ptr) + +Create a new Python wrapping object for a talloc pointer and context, with +py_type as associated Python sub type object. This typically used +when `mem_ctx` and `ptr` differ, e.g. a pointer to an array element. +`pytalloc_get_ptr()` can be used to get the pointer out of the object again. + +This will increment the reference counter for the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_reference(PyTypeObject *py_type, void *talloc_ptr) + +Create a new Python wrapping object for a talloc pointer, with +py_type as associated Python sub type object. The pointer will also be used +as the talloc context. `pytalloc_get_type()` can be used to get +the pointer out of the object again. + +This will increment the reference counter for the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_new(type, PyTypeObject *typeobj) + +Create a new, empty pytalloc_Object with the specified Python type object. type +should be a C type, similar to talloc_new(). + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_GenericObject_steal_ex(void *ptr) + +Create a new Python wrapping object for a generic talloc pointer, +as sub type of `pytalloc_BaseObject`. This typically used +when `mem_ctx` and `ptr` differ, e.g. a pointer to an array element. +`pytalloc_get_ptr()` can be used to get the pointer out of the object again. + +This will *not* increment the reference counter for the talloc context, +so the caller should make sure such an increment has happened. When the Python +object goes away, it will unreference the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_GenericObject_steal(void *ptr) + +Create a new Python wrapping object for a generic talloc pointer, +as sub type of `pytalloc_BaseObject`. The pointer will also be used +as the talloc context. `pytalloc_get_type()` can be used to get +the pointer out of the object again. + +This will *not* increment the reference counter for the talloc context, +so the caller should make sure such an increment has happened. When the Python +object goes away, it will unreference the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_GenericObject_reference_ex(void *ptr) + +Create a new Python wrapping object for a generic talloc pointer, +as sub type of `pytalloc_BaseObject`. This typically used +when `mem_ctx` and `ptr` differ, e.g. a pointer to an array element. +`pytalloc_get_ptr()` can be used to get the pointer out of the object again. + +This will increment the reference counter for the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +PyObject *pytalloc_GenericObject_reference(void *ptr) + +Create a new Python wrapping object for a generic talloc pointer, +as sub type of `pytalloc_BaseObject`. The pointer will also be used +as the talloc context. `pytalloc_get_type()` can be used to get +the pointer out of the object again. + +This will increment the reference counter for the talloc context. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +DEPRECATED! PyObject *pytalloc_CObject_FromTallocPtr(void *); + +Create a new pytalloc_Object for an abitrary talloc-maintained C pointer. This will +use a generic VoidPtr Python type, which just provides an opaque object in +Python. The caller is responsible for incrementing the talloc reference count before calling +this function - it will dereference the talloc pointer when it is garbage collected. + +This function is deprecated and only available on Python 2. +Use pytalloc_GenericObject_{reference,steal}[_ex]() instead. + +Debug function for talloc in Python +----------------------------------- + +The "talloc" module in Python provides a couple of functions that can be used +to debug issues with objects wrapped by pytalloc. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +report_full(obj?) + +Print a full report on a specific object or on all allocated objects by Python. +Same behaviour as the `talloc_report_full()` function that is provided by +C talloc. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +enable_null_tracking() + +This enables tracking of the NULL memory context without enabling leak +reporting on exit. Useful for when you want to do your own leak +reporting call via talloc_report_null_full(). + +This must be done in the top level script, not an imported module. + +=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +pytalloc_total_blocks(obj?) + +Return the talloc block count for all allocated objects or a specific object if +specified. |