[Libguestfs] [nbdkit PATCH v2 5/5] RFC: python: Track and cache per-connection state in C struct
Eric Blake
eblake at redhat.com
Wed Apr 11 05:03:42 UTC 2018
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 at redhat.com>
---
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
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