Re: [Libguestfs] [PATCH nbdkit] python: Implement can_extents + extents.
On Mon, Aug 10, 2020 at 08:07:37AM -0500, Eric Blake wrote:
>+ py_offset = PyTuple_GetItem (t, 0);
>+ py_length = PyTuple_GetItem (t, 1);
>+ py_type = PyTuple_GetItem (t, 2);
>+ extent_offset = PyLong_AsUnsignedLongLong (py_offset);
>+ extent_length = PyLong_AsUnsignedLongLong (py_length);
>+ extent_type = PyLong_AsUnsignedLong (py_type);
>+ if (check_python_failure ("PyLong") == -1) {
Is it really right to be doing error checking only once, but after
three calls into PyLong_* functions? I'm thinking of someone
returning ('a',1,1). But as long as the later successful calls
don't wipe out an earlier failure, this looks like it works.
Yes, the error is thread-local and only cleared by calling
PyErr_Clear().
I modified the test to return ('a', 1, 1) element and it failed:
nbdkit: python: error: test-python-plugin.py: PyLong: error: an integer is required
>+ Py_DECREF (r);
>+ return -1;
>+ }
>+ if (nbdkit_add_extent (extents,
>+ extent_offset, extent_length, extent_type) == -1) {
>+ Py_DECREF (r);
>+ return -1;
>+ }
>+ }
>+
>+ Py_DECREF (r);
>+ }
>+ else {
>+ nbdkit_error ("%s not implemented", "extents");
>+ return -1;
Here, we may be better off doing the same fallback as the C code,
and just reporting the entire image as a single data extent, rather
than always failing.
Yes, good idea, that's an easy change to make.
>+++ b/tests/test_python.py
>@@ -220,3 +232,60 @@ class Test (unittest.TestCase):
> """Test cache."""
> self.connect ({"size": 512, "can_cache":
"native"})
> self.h.cache (512, 0)
>+
>+ # We don't have access to the magic constants defined in the
>+ # nbdkit module, so redefine them here.
>+ EXTENT_HOLE = 1
>+ EXTENT_ZERO = 2
...these constants should have been available through 'import nbdkit'.
Not in this test, because nbdkit isn't a real module, it's one
synthesized in python.c. Perhaps it _should_ be, but that's not how
it's currently implemented.
Otherwise this looks reasonable.
Thanks,
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines. Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top