Bug 807751

In POST:
http://post-office.corp.redhat.com/archives/rhvirt-patches/2012-March/msg02291.html

packages:
libvirt-0.9.10-10.el6.x86_64
libvirt-python-0.9.10-10.el6.x86_64
qemu-kvm-0.12.1.2-2.267.el6ev.x86_64
kernel-2.6.32-257.el6.x86_64

steps:
1. prepare a running domain
2. check with python
# python
Python 2.6.6 (r266:84292, Sep 12 2011, 14:03:14) 
[GCC 4.4.5 20110214 (Red Hat 4.4.5-6)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import libvirt
>>> conn = libvirt.open(None)
>>> dom = conn.lookupByName("rhel6u2")
>>> dom.setSchedulerParameters({'cpu_shares':500})
0
>>> dom.schedulerParameters()
{'vcpu_quota': -1L, 'vcpu_period': 100000L, 'cpu_shares': 500L}
>>> dom.setSchedulerParameters({'cpu_shares': 1000L})
0
>>> dom.schedulerParameters()
{'vcpu_quota': -1L, 'vcpu_period': 100000L, 'cpu_shares': 1000L}
>>> dom.setSchedulerParameters({'cpu_shares': 1000.22})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.6/site-packages/libvirt.py", line 1764, in setSchedulerParameters
    ret = libvirtmod.virDomainSetSchedulerParameters(self._o, params)
TypeError: an integer is required


Things also work fine with setting vcpu_period, but some odd thing happen when setting vcpu_quota.

>>> dom.setSchedulerParameters({'vcpu_quota':-1})
0
>>> dom.schedulerParameters()
{'vcpu_quota': -1L, 'vcpu_period': 100000L, 'cpu_shares': 500L}
>>> dom.setSchedulerParameters({'vcpu_quota': 0.88})
0
>>> dom.setSchedulerParameters({'vcpu_quota': 10.88})
libvir: QEMU error : Unable to set cpu bandwidth quota: Invalid argument
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.6/site-packages/libvirt.py", line 1765, in setSchedulerParameters
    if ret == -1: raise libvirtError ('virDomainSetSchedulerParameters() failed', dom=self)
libvirt.libvirtError: Unable to set cpu bandwidth quota: Invalid argument

So PyLong_AsLongLong treat 0.88 as 0 and 10.88 as 10, maybe error should be throw out here when given float type?

(In reply to comment #5)
> packages:
> libvirt-0.9.10-10.el6.x86_64
> libvirt-python-0.9.10-10.el6.x86_64
> qemu-kvm-0.12.1.2-2.267.el6ev.x86_64
> kernel-2.6.32-257.el6.x86_64

> {'vcpu_quota': -1L, 'vcpu_period': 100000L, 'cpu_shares': 1000L}
> >>> dom.setSchedulerParameters({'cpu_shares': 1000.22})
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/usr/lib64/python2.6/site-packages/libvirt.py", line 1764, in
> setSchedulerParameters
>     ret = libvirtmod.virDomainSetSchedulerParameters(self._o, params)
> TypeError: an integer is required
> 

> >>> dom.setSchedulerParameters({'vcpu_quota': 0.88})
> 0

> 
> So PyLong_AsLongLong treat 0.88 as 0 and 10.88 as 10, maybe error should be
> throw out here when given float type?

Yes, consistency would argue that either we always allow float-to-integer conversions (so setSchedulerParameters:cpu_shares is broken) or never allow it (so setSchedulerParameters:vcpu_quota is broken).  I'm not sure which way python tends to lean; do people like to play fast an loose with automatic floating-point-to-integer truncation, or is it better to be strict and only accept integers?

As far as I know, type-checking in python in not necessary.
If a function is designed to accept both the reference to raw string and integer object, the design is wrong and broken.
The fact is that if you don't know already the type of an object in program, then you are using the function or the program in the wrong way.

For the above example. 'vcpu_quota' need a value of PyInt_type/PyLong_type, but you give the value of Pyfloat_type, you made a mistake first.

From the code speaking, we could give a friendly type-checking, but the type-checking hurts code reuse and reduces performance commonly.

the source code PyLong_AsLongLong

http://svn.python.org/view/python/trunk/Objects/longobject.c?view=markup
http://svn.python.org/view/python/trunk/Include/longintrepr.h?view=markup

I'm going to split this BZ.  The original bug was that we couldn't do dom.setSchedulerParameters with reasonable (integer) arguments; this has been fixed.  The corollary issue (what do we do when setSchedulerParameters is handed unusual arguments, like floating point) is not a show-stopper to 6.3, and should be deferred to 6.4 while upstream decides how to be consistent (either to reject fractional values with a type error, or silently convert them to integers).

According to comment 5 & comment 9, this bug is fixed.
Also testing with latest libvirt(libvirt-0.9.10-15.el6.x86_64) and pass.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2012-0748.html