[Libguestfs] [nbdkit PATCH v2 5/5] RFC: python: Track and cache per-connection state in C struct

Now that we have FUA support, the C code can call can_fua as frequently as on every write. If the python script has a can_fua, we can avoid doubling the calls into python by caching the per-connection results, done by wrapping the python handle in a C struct. This commit is marked RFC because it might be nicer if the C code implemented the caching for ALL plugins (TODO already mentions that). Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- plugins/python/python.c | 83 ++++++++++++++++++++++++++++++------------------- 1 file changed, 51 insertions(+), 32 deletions(-) diff --git a/plugins/python/python.c b/plugins/python/python.c index ad79c80..757a0e9 100644 --- a/plugins/python/python.c +++ b/plugins/python/python.c @@ -389,51 +389,66 @@ py_config_complete (void) return 0; } +/* All per-connection state */ +typedef struct ConnHandle { + PyObject *obj; + int fua; +} ConnHandle; + static void * py_open (int readonly) { PyObject *fn; - PyObject *handle; + ConnHandle *h = malloc (sizeof *h); + if (!h) { + nbdkit_error ("%s: %m", script); + return NULL; + } if (!callback_defined ("open", &fn)) { nbdkit_error ("%s: missing callback: %s", script, "open"); + free (h); return NULL; } PyErr_Clear (); - handle = PyObject_CallFunctionObjArgs (fn, readonly ? Py_True : Py_False, + h->obj = PyObject_CallFunctionObjArgs (fn, readonly ? Py_True : Py_False, NULL); Py_DECREF (fn); - if (check_python_failure ("open") == -1) + if (check_python_failure ("open") == -1) { + free (h); return NULL; + } - return handle; + h->fua = -1; + return h; } static void py_close (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; if (callback_defined ("close", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); check_python_failure ("close"); Py_XDECREF (r); } - Py_DECREF (obj); + Py_DECREF (h->obj); + free (h); } static int64_t py_get_size (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int64_t ret; @@ -445,7 +460,7 @@ py_get_size (void *handle) PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("get_size") == -1) return -1; @@ -462,7 +477,7 @@ static int py_pread (void *handle, void *buf, uint32_t count, uint64_t offset, uint32_t flags) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; @@ -474,7 +489,7 @@ py_pread (void *handle, void *buf, PyErr_Clear (); - r = PyObject_CallFunction (fn, "OiL", obj, count, offset, NULL); + r = PyObject_CallFunction (fn, "OiL", h->obj, count, offset, NULL); Py_DECREF (fn); if (check_python_failure ("pread") == -1) return -1; @@ -504,7 +519,7 @@ static int py_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset, uint32_t flags) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *args; PyObject *kwargs; @@ -516,7 +531,7 @@ py_pwrite (void *handle, const void *buf, if (callback_defined ("pwrite", &fn)) { PyErr_Clear (); - args = Py_BuildValue ("ONL", obj, + args = Py_BuildValue ("ONL", h->obj, PyByteArray_FromStringAndSize (buf, count), offset); if (!args) { @@ -559,7 +574,7 @@ py_pwrite (void *handle, const void *buf, static int py_flush (void *handle, uint32_t flags) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; @@ -567,7 +582,7 @@ py_flush (void *handle, uint32_t flags) if (callback_defined ("flush", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("flush") == -1) return -1; @@ -584,7 +599,7 @@ py_flush (void *handle, uint32_t flags) static int py_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *args; PyObject *kwargs; @@ -596,7 +611,7 @@ py_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags) if (callback_defined ("trim", &fn)) { PyErr_Clear (); - args = Py_BuildValue ("OiL", obj, count, offset); + args = Py_BuildValue ("OiL", h->obj, count, offset); if (!args) { check_python_failure ("trim"); Py_DECREF (fn); @@ -637,7 +652,7 @@ py_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags) static int py_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *args; PyObject *kwargs; @@ -660,7 +675,7 @@ py_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags) PyErr_Clear (); last_error = 0; - args = Py_BuildValue ("OiL", obj, count, offset); + args = Py_BuildValue ("OiL", h->obj, count, offset); if (!args) { check_python_failure ("zero"); Py_DECREF (fn); @@ -718,7 +733,7 @@ py_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags) static int py_can_write (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int ret; @@ -726,7 +741,7 @@ py_can_write (void *handle) if (callback_defined ("can_write", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("can_write") == -1) return -1; @@ -741,7 +756,7 @@ py_can_write (void *handle) static int py_can_flush (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int ret; @@ -749,7 +764,7 @@ py_can_flush (void *handle) if (callback_defined ("can_flush", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("can_flush") == -1) return -1; @@ -764,7 +779,7 @@ py_can_flush (void *handle) static int py_is_rotational (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int ret; @@ -772,7 +787,7 @@ py_is_rotational (void *handle) if (callback_defined ("is_rotational", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("is_rotational") == -1) return -1; @@ -787,7 +802,7 @@ py_is_rotational (void *handle) static int py_can_trim (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int ret; @@ -795,7 +810,7 @@ py_can_trim (void *handle) if (callback_defined ("can_trim", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("can_trim") == -1) return -1; @@ -810,7 +825,7 @@ py_can_trim (void *handle) static int py_can_zero (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int ret; @@ -818,7 +833,7 @@ py_can_zero (void *handle) if (callback_defined ("can_zero", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("can_zero") == -1) return -1; @@ -833,16 +848,20 @@ py_can_zero (void *handle) static int py_can_fua (void *handle) { - PyObject *obj = handle; + ConnHandle *h = handle; PyObject *fn; PyObject *r; int fua; + /* Check the cache first */ + if (h->fua != -1) + return h->fua; + /* We have to convert a python bool into the nbdkit tristate. */ if (callback_defined ("can_fua", &fn)) { PyErr_Clear (); - r = PyObject_CallFunctionObjArgs (fn, obj, NULL); + r = PyObject_CallFunctionObjArgs (fn, h->obj, NULL); Py_DECREF (fn); if (check_python_failure ("can_fua") == -1) return -1; @@ -861,7 +880,7 @@ py_can_fua (void *handle) else fua = NBDKIT_FUA_NONE; - return fua; + return h->fua = fua; } #define py_config_help \ -- 2.14.3