On Wed, Aug 11, 2010 at 8:25 AM, Dhaval Giani <[email protected]> wrote:
>
> On Tue, Aug 10, 2010 at 9:38 PM, Jason Baron <[email protected]> wrote:
> > Hi,
> >
> > I was playing around with the language bindings mentioned in: Subject:
> > [Libcg-devel] [hack] Language bindings for libcgroup
> >
> > I was just trying to figure out how to call the
> > "cgroup_read_stats_begin()" function from python. The third argument
> > takes a 'void **'. How can I call this function in python?
> >
> > I've posted my full test script (building on the one you posted) below.
> > The error I'm currently getting is:
> >
> > Traceback (most recent call last):
> > File "./tester.py", line 20, in <module>
> > cgroup_read_stats_begin("cpu", "/cgroup/test", byref(handle), cg_stat)
> > TypeError: in method 'cgroup_read_stats_begin', argument 3 of type 'void **'
> >
>
> I i read your script corectly, you are passing a void * as opposed to
> a void **. Not sure hwo to fix it in python though.
>
No, that's not it, we need to create typemaps. Jason could you please
add the following typemap in libcgroup.i before the "C" prototypes and
structures
%typemap (in) void** (void *temp) {
void *arg;
if ((arg = PyCObject_AsVoidPtr($input)) != NULL) {
$1 = &arg;
} else
$1 = &temp;
}
%typemap (argout) void** {
PyObject *obj = PyCObject_FromVoidPtr(*$1, NULL);
$result = PyTuple_Pack(2, $result, obj);
}
Recompile the swig module and the libcgroup_wrap.c file.
Then could you try the following python script
#!/usr/bin/python
from libcgroup import *
from ctypes import *
cgroup_init()
#
# Add the correct controllers based on the mount point
#
cg_stat = cgroup_stat()
p = c_void_p()
ret, p = cgroup_read_stats_begin("memory", "/", p, cg_stat)
while ret != ECGEOF:
print "%s:%s" %(cg_stat.name, cg_stat.value)
ret, p = cgroup_read_stats_next(p, cg_stat)
cgroup_read_stats_end(p)
NOTE: The return values are twisted, the void **handle needs to be
reloaded back using ret, p
NOTE: I've not checked the program for leaks at the moment
Please do report back if this works for you. This should potentially
solve most of the void** issues we have passing data between libcgroup
and python wrappers back and forth
Balbir
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