[libvirt] [PATCH v1 1/2] Allow for ff callbacks to be called by custom event implementations
Wojtek Porczyk
woju at invisiblethingslab.com
Fri Mar 17 01:16:25 UTC 2017
The documentation says:
> If the opaque user data requires free'ing when the handle is
> unregistered, then a 2nd callback can be supplied for this purpose.
> This callback needs to be invoked from a clean stack. If 'ff'
> callbacks are invoked directly from the virEventRemoveHandleFunc they
> will likely deadlock in libvirt.
And they did deadlock. In removeTimeout too. Now we supply a custom
function to pick it from the opaque blob and fire.
Signed-off-by: Wojtek Porczyk <woju at invisiblethingslab.com>
---
libvirt-override.c | 36 ++++++++++++------------------------
libvirt-override.py | 39 +++++++++++++++++++++++++++++++++++++++
sanitytest.py | 5 +++--
3 files changed, 54 insertions(+), 26 deletions(-)
diff --git a/libvirt-override.c b/libvirt-override.c
index 9e40f00..37f7ee2 100644
--- a/libvirt-override.c
+++ b/libvirt-override.c
@@ -5223,6 +5223,9 @@ libvirt_virEventAddHandleFunc(int fd,
VIR_PY_TUPLE_SET_GOTO(pyobj_args, 3, cb_args, cleanup);
+ /* If changing contents of the opaque object, please also change
+ * virEventExecuteFFCallback() in libvirt-override.py
+ */
VIR_PY_TUPLE_SET_GOTO(cb_args, 0, libvirt_virEventHandleCallbackWrap(cb), cleanup);
VIR_PY_TUPLE_SET_GOTO(cb_args, 1, libvirt_virVoidPtrWrap(opaque), cleanup);
VIR_PY_TUPLE_SET_GOTO(cb_args, 2, libvirt_virFreeCallbackWrap(ff), cleanup);
@@ -5292,20 +5295,11 @@ libvirt_virEventRemoveHandleFunc(int watch)
VIR_PY_TUPLE_SET_GOTO(pyobj_args, 0, libvirt_intWrap(watch), cleanup);
result = PyEval_CallObject(removeHandleObj, pyobj_args);
- if (!result) {
+ if (result) {
+ retval = 0;
+ } else {
PyErr_Print();
PyErr_Clear();
- } else if (!PyTuple_Check(result) || PyTuple_Size(result) != 3) {
- DEBUG("%s: %s must return opaque obj registered with %s"
- "to avoid leaking libvirt memory\n",
- __FUNCTION__, NAME(removeHandle), NAME(addHandle));
- } else {
- opaque = PyTuple_GetItem(result, 1);
- ff = PyTuple_GetItem(result, 2);
- cff = PyvirFreeCallback_Get(ff);
- if (cff)
- (*cff)(PyvirVoidPtr_Get(opaque));
- retval = 0;
}
cleanup:
@@ -5350,6 +5344,9 @@ libvirt_virEventAddTimeoutFunc(int timeout,
VIR_PY_TUPLE_SET_GOTO(pyobj_args, 2, cb_args, cleanup);
+ /* If changing contents of the opaque object, please also change
+ * virEventExecuteFFCallback() in libvirt-override.py
+ */
VIR_PY_TUPLE_SET_GOTO(cb_args, 0, libvirt_virEventTimeoutCallbackWrap(cb), cleanup);
VIR_PY_TUPLE_SET_GOTO(cb_args, 1, libvirt_virVoidPtrWrap(opaque), cleanup);
VIR_PY_TUPLE_SET_GOTO(cb_args, 2, libvirt_virFreeCallbackWrap(ff), cleanup);
@@ -5416,20 +5413,11 @@ libvirt_virEventRemoveTimeoutFunc(int timer)
VIR_PY_TUPLE_SET_GOTO(pyobj_args, 0, libvirt_intWrap(timer), cleanup);
result = PyEval_CallObject(removeTimeoutObj, pyobj_args);
- if (!result) {
+ if (result) {
+ retval = 0;
+ } else {
PyErr_Print();
PyErr_Clear();
- } else if (!PyTuple_Check(result) || PyTuple_Size(result) != 3) {
- DEBUG("%s: %s must return opaque obj registered with %s"
- "to avoid leaking libvirt memory\n",
- __FUNCTION__, NAME(removeTimeout), NAME(addTimeout));
- } else {
- opaque = PyTuple_GetItem(result, 1);
- ff = PyTuple_GetItem(result, 2);
- cff = PyvirFreeCallback_Get(ff);
- if (cff)
- (*cff)(PyvirVoidPtr_Get(opaque));
- retval = 0;
}
cleanup:
diff --git a/libvirt-override.py b/libvirt-override.py
index 63f8ecb..3d09d63 100644
--- a/libvirt-override.py
+++ b/libvirt-override.py
@@ -16,6 +16,7 @@ except ImportError:
if str(cyg_e).count("No module named"):
raise lib_e
+import ctypes
import types
# The root of all libvirt errors.
@@ -211,3 +212,41 @@ def virEventAddTimeout(timeout, cb, opaque):
ret = libvirtmod.virEventAddTimeout(timeout, cbData)
if ret == -1: raise libvirtError ('virEventAddTimeout() failed')
return ret
+
+
+#
+# a caller for the ff callbacks for custom event loop implementations
+#
+
+ctypes.pythonapi.PyCapsule_GetPointer.restype = ctypes.c_void_p
+ctypes.pythonapi.PyCapsule_GetPointer.argtypes = (
+ ctypes.py_object, ctypes.c_char_p)
+
+_virFreeCallback = ctypes.CFUNCTYPE(None, ctypes.c_void_p)
+
+def virEventExecuteFFCallback(opaque):
+ """
+ Execute callback which frees the opaque buffer
+
+ @opaque: the opaque object passed to addHandle or addTimeout
+
+ WARNING: This function should not be called from any call by libvirt's
+ core. It will most probably cause deadlock in C-level libvirt code.
+ Instead it should be scheduled and called from implementation's stack.
+
+ See https://libvirt.org/html/libvirt-libvirt-event.html#virEventAddHandleFunc
+ for more information.
+
+ This function is not dependent on any event loop implementation.
+ """
+ # The opaque object is really a 3-tuple, which contains a the real opaque
+ # pointer and the ff callback, both of which are inside PyCapsules. If not
+ # specified, the ff may be None. See libvirt-override.c.
+
+ dummy, caps_opaque, caps_ff = opaque
+ ff = _virFreeCallback(ctypes.pythonapi.PyCapsule_GetPointer(
+ caps_ff, "virFreeCallback".encode("ascii")))
+ if ff:
+ real_opaque = ctypes.pythonapi.PyCapsule_GetPointer(
+ caps_opaque, "void*".encode("ascii"))
+ ff(real_opaque)
diff --git a/sanitytest.py b/sanitytest.py
index a140ba2..6548831 100644
--- a/sanitytest.py
+++ b/sanitytest.py
@@ -345,11 +345,12 @@ for name in sorted(finalklassmap):
# Phase 6: Validate that every python API has a corresponding C API
for klass in gotfunctions:
- if klass == "libvirtError":
+ if klass in ("libvirtError", "virEventAsyncIOImpl"):
continue
for func in sorted(gotfunctions[klass]):
# These are pure python methods with no C APi
- if func in ["connect", "getConnect", "domain", "getDomain"]:
+ if func in ["connect", "getConnect", "domain", "getDomain",
+ "virEventRegisterAsyncIOImpl"]:
continue
key = "%s.%s" % (klass, func)
--
2.5.5
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