A little over 5 years ago now, I wrote about a how libvirt introduced support for QCow2 built-in encryption. The use cases for built-in qcow2 encryption were compelling back then, and remain so today. In particular while LUKS is fine if your disk backend is already a kernel visible block device, it is not a generically usable alternative for QEMU since it requires privileged operation to set it up, would require yet another I/O layer via a loopback or qemu-nbd device, and finally is entirely Linux specific. The direction QEMU has taken over the past few years has in fact been to take the kernel out of the equation for more & more functionality. For example, QEMU can now natively connect to RBD, Gluster, iSCSI and NFS servers with no kernel assistance – the client code is implemented entirely within QEMU block driver layer, which precludes the use of LUKS there.
At the time I wrote that blog post, no one had seriously looked at the QCow2 encryption design to see if it was in any way sane from a security POV. At least if they had, AFAIK, they didn’t make their analysis public. Over time though, various QEMU maintainers did eventually look at the QCow2 encryption code and their conclusions were not positive. The consensus opinion amongst QEMU maintainers today is that QCow2 encryption is terminally flawed in a number of serious ways, including but not limited to:
- The AES-CBC cipher is used with predictable initialization vectors based on the sector number. This makes it vulnerable to chosen plaintext attacks which can reveal the existence of encrypted data.
- The user passphrase is directly used as the encryption key.
- A poorly chosen or short passphrase will compromise the security of the encryption.
- In the event of the passphrase being compromised there is no way to change the passphrase to protect data in any qcow images.
- It is difficult to make the data permanently inaccessible upon file deletion – at best you can try to destroy data with shred, though even this is ineffective with many modern storage technologies.
By comparison the LUKS encryption format does not suffer from any of these problems. With LUKS the initialization vectors typically use ESSIV to ensure unpredictability; the passphrase is only indirectly used to unlock the master encryption key material, so can be changed at will; the passphrase is put through a PBKDF2 function to mitigate the effects of short sequences of letters; the size of the master key material is artificially inflated with an anti-forensic algorithm to increase the difficulty of recovering the key from deleted volumes.
The QCow2 encryption scheme is a prime example of why merely using a well known standard algorithm (AES) is not sufficient to guarantee a secure implementation. In January 2014, I submitted an update for the QEMU docs to explicitly warn users about the security limitations of QCow2 encryption, which made it into the 1.5.0 release of QEMU. This week Markus has gone one step further and explicitly deprecated use of QCow2 encryption for the forthcoming 2.3.0 release of QEMU. Any attempt to use an encrypted QCow2 file with the QEMU system emulator will now result in a warning being printed to stderr, which in turn ends up in the libvirt logfile for that guest. As well as the security issues, Markus’ other motivation for deprecating this is that the way it is integrated into QEMU block driver layer causes a number of technical & usability problems. So even if we want encrypted block devices in QEMU, the internals for encryption need a complete rewrite from scratch.
In the 2.4.0 release, the intention is to go one step further and actually delete support for QCow2 encryption from the QEMU system emulator entirely, as well as all the infrastructure for block device encryption. We will keep support for decrypting images in the qemu-img program only, to provide a way for users to get their previously encrypted data out into a supported format.
In the immediate future, the recommendation is that users who need encryption for virtual disks should use LUKS on the host, despite the limitations that I noted earlier. At some point in the next 6 months my intention is to start working on a QEMU block driver implementation of the LUKS format, which will enable QEMU to add encryption to any of its virtual disk backends, not merely QCow2. This will require designing new infrastructure for handling decryption keys inside QEMU too, to replace the unsatisfactory approach used today. By using the LUKS format directly though, QEMU will benefit from the security knowledge of those who designed and analysed this format over many years to identify its strengths & weaknesses. It will also provide good interoperability. eg an encrypted qcow2-luks file will be able to be converted to/from a block device for access by the kernel’s LUKS driver with no need to re-encrypt the data, which is very desirable as it lets users decide whether to use in-QEMU or in-kernel block device backends at the flick of a switch.
So just to sum up. Do not ever use QCow2 built-in encryption as it exists today. It is unfixably broken by design. It is deprecated in QEMU 2.3.0 and is likely to be deleted in QEMU 2.4.0.
One of the issues encountered when debugging libvirt guest problems with Nova, is that it isn’t always entirely obvious why the guest XML is configured the way it is. For a while now, libvirt has had the ability to record arbitrary application specific metadata in the guest XML. Each application simply declares the XML namespace it wishes to use and can then record whatever it wants. Libvirt will treat this metadata as a black box, never attempting to interpret or modify it. In the Juno release I worked on a blueprint to make use of this feature to record some interesting information about Nova.
The initial set of information recorded is as follows:
- Version – the Nova version number, and any vendor specific package suffiix (eg RPM release number). This is useful as the user reporting a bug is often not entirely clear what particular RPM version was installed when the guest was first booted.
- Name – the Nova instance display name. While you can correlated Nova instances to libvirt guests using the UUID, users reporting bugs often only tell you the display name. So recording this in the XML is handy to correlate which XML config corresponds to which Nova guest they’re talking about.
- Creation time – the time at which Nova booted the guest. Sometimes useful when trying to understand the sequence in which things happened.
- Flavour – the Nova flavour name, memory, disk, swap, ephemeral and vcpus settings. Flavours can be changed by the admin after a guest is booted, so having the original values recorded against the guest XML is again handy.
- Owner – the tenant user ID and name, as well as their project
- Root image – the glance image ID, if the guest was booted from an image
The Nova version number information in particular has already proved very useful in a couple of support tickets, showing that the VM instance was not booted under the software version that was initially claimed. There is still scope for augmenting this information further though. When working on another support issues it would have been handy to know the image properties and flavour extra specs that were set, as the user’s bug report also gave misleading / incorrect information in this area. Information about cinder block devices would also be useful to have access to, for cases where the guest isn’t booting from an image.
While all this info is technically available from the Nova database, it is far easier (and less dangerous) to ask the user to provide the libvirt XML configuration than to have them run random SQL queries. Standard OS trouble shooting tools such as sosreport from RHEL/Fedora already collect the libvirt guest XML when run. As a result, the bug report is more likely to contain this useful data in the initial filing, avoiding the need to ask the user to collect further data after the fact.
To give an example of what the data looks like, a Nova guest booted with
$ nova boot --image cirros-0.3.0-x86_64-uec --flavor m1.tiny vm1
Gets the following data recorded
$ virsh -c qemu:///system dumpxml instance-00000001
<domain type='kvm' id='2'>
<name>instance-00000001</name>
<uuid>d0e51bbd-cbbd-4abc-8f8c-dee2f23ded12</uuid>
<metadata>
<nova:instance xmlns:nova="http://openstack.org/xmlns/libvirt/nova/1.0">
<nova:package version="2015.1"/>
<nova:name>vm1</nova:name>
<nova:creationTime>2015-02-19 18:23:44</nova:creationTime>
<nova:flavor name="m1.tiny">
<nova:memory>512</nova:memory>
<nova:disk>1</nova:disk>
<nova:swap>0</nova:swap>
<nova:ephemeral>0</nova:ephemeral>
<nova:vcpus>1</nova:vcpus>
</nova:flavor>
<nova:owner>
<nova:user uuid="ef53a6031fc643f2af7add439ece7e9d">admin</nova:user>
<nova:project uuid="60a60883d7de429aa45f8f9d689c1fd6">demo</nova:project>
</nova:owner>
<nova:root type="image" uuid="2344a0fc-a34b-4e2d-888e-01db795fc89a"/>
</nova:instance>
</metadata>
...snip...
</domain>
The intention is that as long as the XML namespace URI (http://openstack.org/xmlns/libvirt/nova/1.0) isn’t changed, the data reported here will not change in a backwards incompatible manner. IOW, we will add further elements or attributes to the Nova metadata, but not change or remove existing elements or attributes. So if OpenStack related troubleshooting / debugging tools want to extract this data from the libvirt XML they can be reasonably well assured of compatibility across future Nova releases.
In the Kilo development cycle there have been patches submitted to record similar kind of data for VMWare guests, though obviously it uses a config data format relevant to VMWare rather than XML. Sadly this useful debugging improvement for VMWare had its feature freeze exception request rejected, pushing it out to Liberty, which is rather a shame :-(
This blogs describes a error reporting / troubleshooting feature added to Nova a while back which people are probably not generally aware of.
One of the early things I worked on in the Nova libvirt driver was integration of support for the libvirt event notification system. This allowed Nova to get notified when instances are shutdown by the guest OS administrator, instead of having to wait for the background power state sync task to run. Supporting libvirt events was a theoretically simple concept, but in practice there was a nasty surprise. The key issue was that we needed to have a native thread running the libvirt event loop, while the rest of Nova uses green threads. The code kept getting bizarre deadlocks, which were eventually traced to use of the python logging APIs in the native thread. Since eventlet had monkeypatched the thread mutex primitives, the logging APIs couldn’t be safely called from the native thread as they’d try to obtain a green mutex from a native thread context.
Eventlet has a concept of a backdoor port, which lets you connect to the python process using telnet and get an interactive python prompt. After turning this on, I got a stack trace of all green and native threads and eventually figured out the problem, which was great. Sadly the eventlet backdoor is not something anyone sane would ever enable out of the box on production systems – you don’t really want to allow remote command execution to anyone who can connect to a TCP port :-) Another debugging option is to use Python’s native debugger, but this is again something you have to enable ahead of time and won’t be something admins enable out of the box on production systems. It is possible to connect to a running python process with GDB and get a crude stack trace, but that’s not great either as it requires python debuginfo libraries installed. It would be possible to build an administrative debugging API for Nova using the REST API, but that only works if the REST API & message bus are working – not something that’s going to be much use when Nova itself has deadlocked the entire python interpretor
After this debugging experience I decided to propose something that I’ve had on previous complex systems, a facility that allows an admin to trigger a live error report. Crucially this facility must not require any kind of deployment setup tasks and thus be guaranteed available at all times, especially on production systems where debugging options are limited by the need to maintain service to users. I called the proposal the “Guru Meditation Report” in reference to old Amiga crash reports. I did a quick proof of concept to test the idea, but Solly Ross turned the idea into a complete feature for OpenStack, adding it to the Oslo Incubator in the openstack.common.reports namespace and integrating with Nova. This shipped with the Icehouse release of Nova.
Service integration & usage
Integration into projects is quite straightforward, the openstack-common.conf file needs to list the relevant modules to import from oslo-incubator
$ grep report openstack-common.conf
module=report
module=report.generators
module=report.models
module=report.views
module=report.views.json
module=report.views.text
module=report.views.xml
then each service process needs to initialize the error report system. This just requires a single import line and method call from the main method
$ cat nova/cmd/nova-compute
...snip...
from nova.openstack.common.report import guru_meditation_report as gmr
...snip...
def main():
gmr.TextGuruMeditation.setup_autorun(version)
...run eventlet service or whatever...
The setup_autorun method installs a signal handler connected to SIGUSR1 which will dump an error report to stderr when triggered.
So from Icehouse onwards, if any Nova process is mis-behaving you can simply run something like
$ kill -USR1 `pgrep nova-compute`
to get a detailed error report of the process state sent to stderr. On RHEL-7 / Fedora systems this data should end up going into the systemd journal for that service. On other systems you may be lucky enough for the init service to have redirected stderr to a log file, or unlucky enough to have it sent to /dev/null. Did I mention the systemd journal is a really exactly feature when troubleshooting service problems :-)
Error report information
In the oslo-incubator code there are 5 standard sections defined for the error report
- Config – dump of all configuration settings loaded by oslo.config – useful because the config settings loaded in memory don’t necessarily match what is currently stored in /etc/nova/nova.conf on disk – eg admin may have modified the config and forgotten to reload the services.
- Package – information about the software package, as passed into the setup_autorun method previously. This lets you know the openstack release version number, the vendor who packaged it and any vendor specific version info such as the RPM release number. This is again key, because what’s installed on the host currently may not match the version that’s actually running. You can’t always trust the admins to give you correct info when reporting bugs, so having software report itself is more reliable.
- Process – information about the running process including the process ID, parent process ID, user ID, group ID and scheduler state.
- Green Threads – stack trace of every eventlet green thread currently in existence
- Native Threads – stack trace of every native thread currently in existence
The report framework is modular, so it is possible to register new generator functions which add further data to the error report. This is useful if there is application specific data that is useful to include, that would not otherwise be suitable for inclusion in oslo-incubator directly. The data model is separated from the output formatting code, so it is possible to output the report in a number of different data formats. The reports which get sent to stderr are using a crude plain text format, but it is possible to have reports generated in XML, JSON, or another completely custom format.
Future improvements
Triggering from a UNIX signal and printing to stderr, is a very simple and reliable approach that we can guarantee will almost always work no matter what operational state the OpenStack deployment as a whole is in. It should not be considered the only possible approach though. I can see that it may be desirable to also wire this up to RPC messaging bus, so a cloud admin can remotely generate an error report for a service and get the response back over the message bus in an XML or JSON format. This wouldn’t replace the SIGUSR1 based stderr dumps, but rather augment them, as we want to retain the ability to trigger reports even if rabbitmq bus connection is dead/broken for some reason.
AFAIK, this error report system is only wired up into the Nova project at this time. It is desirable to bring this feature over to projects like Neutron, Cinder, Glance, Keystone too, so it can be a considered an openstack wide standard system for admins to collect data for troubleshooting. As explained above, this is no more difficult that adding the modules to openstack-common.conf and then adding a single method call to the service startup main method. Those projects might like to register extra error report sections to provide further data, but that’s by no means required for initial integration.
Having error reports triggered on demand by the admin is nice, but I think there is also value in having error reports triggered automatically in response to unexpected error conditions. For example if a RPC request to boot a new VM instance fails, it could be desirable to save a detailed error report, rather than just having an exception hit the logs with no context around it. In such a scenario you would extend the error report generator so that the report included the exception information & stack trace, and also include the headers and/or payload of the RPC request that failed. The error report would probably be written to a file instead of stderr, using JSON or XML. Tools could then be written to analyse error reports and identify commonly recurring problems.
Even with the current level of features for the error report system, it has proved its worth in facilitating the debugging of a number of problems in Nova, where things like the eventlet backdoor or python debugger were impractical to use. I look forward to its continued development and broader usage across openstack.
Example report
What follows below is an example error report from the nova-compute service running in one of my development hosts. Notice that oslo.conf configuration parameters that were declared with the ‘secret’ flag have their value masked. This is primarily aiming to prevent passwords making their way into the error report, since the expectation is the users may attach these reports to public bugs.
========================================================================
==== Guru Meditation ====
========================================================================
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
========================================================================
==== Package ====
========================================================================
product = OpenStack Nova
vendor = OpenStack Foundation
version = 2015.1
========================================================================
==== Threads ====
========================================================================
------ Thread #140157298652928 ------
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------ Thread #140157734876928 ------
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------ Thread #140158288500480 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140158416287488 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140158424680192 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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`self.run()`
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`self.__target(*self.__args, **self.__kwargs)`
/home/berrange/src/cloud/nova/nova/virt/libvirt/host.py:113 in _native_thread
`libvirt.virEventRunDefaultImpl()`
/usr/lib64/python2.7/site-packages/libvirt.py:340 in virEventRunDefaultImpl
`ret = libvirtmod.virEventRunDefaultImpl()`
------ Thread #140157684520704 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140158296893184 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
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------ Thread #140158305285888 ------
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------ Thread #140157709698816 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140158322071296 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140157726484224 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140158330464000 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140157332223744 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
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------ Thread #140157701306112 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
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`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
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`waiter.acquire()`
------ Thread #140157692913408 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
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`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
/usr/lib64/python2.7/Queue.py:168 in get
`self.not_empty.wait()`
/usr/lib64/python2.7/threading.py:339 in wait
`waiter.acquire()`
------ Thread #140157315438336 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
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`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
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`waiter.acquire()`
------ Thread #140158537955136 ------
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:346 in run
`self.wait(sleep_time)`
/usr/lib/python2.7/site-packages/eventlet/hubs/poll.py:85 in wait
`presult = self.do_poll(seconds)`
/usr/lib/python2.7/site-packages/eventlet/hubs/epolls.py:62 in do_poll
`return self.poll.poll(seconds)`
------ Thread #140158313678592 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
/usr/lib64/python2.7/threading.py:764 in run
`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
/usr/lib64/python2.7/Queue.py:168 in get
`self.not_empty.wait()`
/usr/lib64/python2.7/threading.py:339 in wait
`waiter.acquire()`
------ Thread #140157718091520 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
/usr/lib64/python2.7/threading.py:764 in run
`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
/usr/lib64/python2.7/Queue.py:168 in get
`self.not_empty.wait()`
/usr/lib64/python2.7/threading.py:339 in wait
`waiter.acquire()`
------ Thread #140157323831040 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
/usr/lib64/python2.7/threading.py:764 in run
`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
/usr/lib64/python2.7/Queue.py:168 in get
`self.not_empty.wait()`
/usr/lib64/python2.7/threading.py:339 in wait
`waiter.acquire()`
------ Thread #140158338856704 ------
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
/usr/lib64/python2.7/threading.py:764 in run
`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/eventlet/tpool.py:72 in tworker
`msg = _reqq.get()`
/usr/lib64/python2.7/Queue.py:168 in get
`self.not_empty.wait()`
/usr/lib64/python2.7/threading.py:339 in wait
`waiter.acquire()`
========================================================================
==== Green Threads ====
========================================================================
------ Green Thread ------
/usr/bin/nova-compute:9 in <module>
`load_entry_point('nova==2015.1.dev352', 'console_scripts', 'nova-compute')()`
/home/berrange/src/cloud/nova/nova/cmd/compute.py:74 in main
`service.wait()`
/home/berrange/src/cloud/nova/nova/service.py:444 in wait
`_launcher.wait()`
/home/berrange/src/cloud/nova/nova/openstack/common/service.py:187 in wait
`status, signo = self._wait_for_exit_or_signal(ready_callback)`
/home/berrange/src/cloud/nova/nova/openstack/common/service.py:170 in _wait_for_exit_or_signal
`super(ServiceLauncher, self).wait()`
/home/berrange/src/cloud/nova/nova/openstack/common/service.py:133 in wait
`self.services.wait()`
/home/berrange/src/cloud/nova/nova/openstack/common/service.py:473 in wait
`self.tg.wait()`
/home/berrange/src/cloud/nova/nova/openstack/common/threadgroup.py:145 in wait
`x.wait()`
/home/berrange/src/cloud/nova/nova/openstack/common/threadgroup.py:47 in wait
`return self.thread.wait()`
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:175 in wait
`return self._exit_event.wait()`
/usr/lib/python2.7/site-packages/eventlet/event.py:121 in wait
`return hubs.get_hub().switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
No Traceback!
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/green/thread.py:40 in __thread_body
`func(*args, **kwargs)`
/usr/lib64/python2.7/threading.py:784 in __bootstrap
`self.__bootstrap_inner()`
/usr/lib64/python2.7/threading.py:811 in __bootstrap_inner
`self.run()`
/usr/lib64/python2.7/threading.py:764 in run
`self.__target(*self.__args, **self.__kwargs)`
/usr/lib/python2.7/site-packages/qpid/selector.py:126 in run
`rd, wr, ex = select(self.reading, self.writing, (), timeout)`
/usr/lib/python2.7/site-packages/eventlet/green/select.py:83 in select
`return hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:214 in main
`result = function(*args, **kwargs)`
/home/berrange/src/cloud/nova/nova/openstack/common/service.py:492 in run_service
`done.wait()`
/usr/lib/python2.7/site-packages/eventlet/event.py:121 in wait
`return hubs.get_hub().switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:214 in main
`result = function(*args, **kwargs)`
/home/berrange/src/cloud/nova/nova/virt/libvirt/host.py:124 in _dispatch_thread
`self._dispatch_events()`
/home/berrange/src/cloud/nova/nova/virt/libvirt/host.py:228 in _dispatch_events
`_c = self._event_notify_recv.read(1)`
/usr/lib64/python2.7/socket.py:380 in read
`data = self._sock.recv(left)`
/usr/lib/python2.7/site-packages/eventlet/greenio.py:464 in recv
`self._trampoline(self, read=True)`
/usr/lib/python2.7/site-packages/eventlet/greenio.py:439 in _trampoline
`mark_as_closed=self._mark_as_closed)`
/usr/lib/python2.7/site-packages/eventlet/hubs/__init__.py:162 in trampoline
`return hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/tpool.py:55 in tpool_trampoline
`_c = _rsock.recv(1)`
/usr/lib/python2.7/site-packages/eventlet/greenio.py:325 in recv
`timeout_exc=socket.timeout("timed out"))`
/usr/lib/python2.7/site-packages/eventlet/greenio.py:200 in _trampoline
`mark_as_closed=self._mark_as_closed)`
/usr/lib/python2.7/site-packages/eventlet/hubs/__init__.py:162 in trampoline
`return hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:214 in main
`result = function(*args, **kwargs)`
/usr/lib/python2.7/site-packages/oslo_utils/excutils.py:92 in inner_func
`return infunc(*args, **kwargs)`
/usr/lib/python2.7/site-packages/oslo_messaging/_executors/impl_eventlet.py:93 in _executor_thread
`incoming = self.listener.poll()`
/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/amqpdriver.py:121 in poll
`self.conn.consume(limit=1, timeout=timeout)`
/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/impl_qpid.py:755 in consume
`six.next(it)`
/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/impl_qpid.py:685 in iterconsume
`yield self.ensure(_error_callback, _consume)`
/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/impl_qpid.py:602 in ensure
`return method()`
/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/impl_qpid.py:669 in _consume
`timeout=poll_timeout)`
<string>:6 in next_receiver
(source not found)
/usr/lib/python2.7/site-packages/qpid/messaging/endpoints.py:674 in next_receiver
`if self._ecwait(lambda: self.incoming, timeout):`
/usr/lib/python2.7/site-packages/qpid/messaging/endpoints.py:50 in _ecwait
`result = self._ewait(lambda: self.closed or predicate(), timeout)`
/usr/lib/python2.7/site-packages/qpid/messaging/endpoints.py:580 in _ewait
`result = self.connection._ewait(lambda: self.error or predicate(), timeout)`
/usr/lib/python2.7/site-packages/qpid/messaging/endpoints.py:218 in _ewait
`result = self._wait(lambda: self.error or predicate(), timeout)`
/usr/lib/python2.7/site-packages/qpid/messaging/endpoints.py:197 in _wait
`return self._waiter.wait(predicate, timeout=timeout)`
/usr/lib/python2.7/site-packages/qpid/concurrency.py:59 in wait
`self.condition.wait(timeout - passed)`
/usr/lib/python2.7/site-packages/qpid/concurrency.py:96 in wait
`sw.wait(timeout)`
/usr/lib/python2.7/site-packages/qpid/compat.py:53 in wait
`ready, _, _ = select([self], [], [], timeout)`
/usr/lib/python2.7/site-packages/eventlet/green/select.py:83 in select
`return hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/home/berrange/src/cloud/nova/nova/openstack/common/loopingcall.py:90 in _inner
`greenthread.sleep(-delay if delay < 0 else 0)`
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:34 in sleep
`hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
------ Green Thread ------
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:214 in main
`result = function(*args, **kwargs)`
/home/berrange/src/cloud/nova/nova/openstack/common/loopingcall.py:133 in _inner
`greenthread.sleep(idle)`
/usr/lib/python2.7/site-packages/eventlet/greenthread.py:34 in sleep
`hub.switch()`
/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py:294 in switch
`return self.greenlet.switch()`
========================================================================
==== Processes ====
========================================================================
Process 27760 (under 27711) [ run by: berrange (1000), state: running ]
========================================================================
==== Configuration ====
========================================================================
cells:
bandwidth_update_interval = 600
call_timeout = 60
capabilities =
hypervisor=xenserver;kvm
os=linux;windows
cell_type = compute
enable = False
manager = nova.cells.manager.CellsManager
mute_child_interval = 300
name = nova
reserve_percent = 10.0
topic = cells
cinder:
cafile = None
catalog_info = volumev2:cinderv2:publicURL
certfile = None
cross_az_attach = True
endpoint_template = None
http_retries = 3
insecure = False
keyfile = None
os_region_name = None
timeout = None
conductor:
manager = nova.conductor.manager.ConductorManager
topic = conductor
use_local = False
workers = None
database:
backend = sqlalchemy
connection = ***
connection_debug = 0
connection_trace = False
db_inc_retry_interval = True
db_max_retries = 20
db_max_retry_interval = 10
db_retry_interval = 1
idle_timeout = 3600
max_overflow = None
max_pool_size = None
max_retries = 10
min_pool_size = 1
mysql_sql_mode = TRADITIONAL
pool_timeout = None
retry_interval = 10
slave_connection = ***
sqlite_db = nova.sqlite
sqlite_synchronous = True
use_db_reconnect = False
use_tpool = False
default:
allow_migrate_to_same_host = True
allow_resize_to_same_host = True
allow_same_net_traffic = True
amqp_auto_delete = False
amqp_durable_queues = False
api_paste_config = /etc/nova/api-paste.ini
api_rate_limit = False
auth_strategy = keystone
auto_assign_floating_ip = False
backdoor_port = None
bandwidth_poll_interval = 600
bindir = /usr/bin
block_device_allocate_retries = 60
block_device_allocate_retries_interval = 3
boot_script_template = /home/berrange/src/cloud/nova/nova/cloudpipe/bootscript.template
ca_file = cacert.pem
ca_path = /home/berrange/src/cloud/data/nova/CA
cert_manager = nova.cert.manager.CertManager
client_socket_timeout = 900
cnt_vpn_clients = 0
compute_available_monitors =
nova.compute.monitors.all_monitors
compute_driver = libvirt.LibvirtDriver
compute_manager = nova.compute.manager.ComputeManager
compute_monitors =
compute_resources =
vcpu
compute_stats_class = nova.compute.stats.Stats
compute_topic = compute
config-dir = None
config-file =
/etc/nova/nova.conf
config_drive_format = iso9660
config_drive_skip_versions = 1.0 2007-01-19 2007-03-01 2007-08-29 2007-10-10 2007-12-15 2008-02-01 2008-09-01
console_host = mustard.gsslab.fab.redhat.com
console_manager = nova.console.manager.ConsoleProxyManager
console_topic = console
consoleauth_manager = nova.consoleauth.manager.ConsoleAuthManager
consoleauth_topic = consoleauth
control_exchange = nova
create_unique_mac_address_attempts = 5
crl_file = crl.pem
db_driver = nova.db
debug = True
default_access_ip_network_name = None
default_availability_zone = nova
default_ephemeral_format = ext4
default_flavor = m1.small
default_floating_pool = public
default_log_levels =
amqp=WARN
amqplib=WARN
boto=WARN
glanceclient=WARN
iso8601=WARN
keystonemiddleware=WARN
oslo.messaging=INFO
qpid=WARN
requests.packages.urllib3.connectionpool=WARN
routes.middleware=WARN
sqlalchemy=WARN
stevedore=WARN
suds=INFO
urllib3.connectionpool=WARN
websocket=WARN
default_notification_level = INFO
default_publisher_id = None
default_schedule_zone = None
defer_iptables_apply = False
dhcp_domain = novalocal
dhcp_lease_time = 86400
dhcpbridge = /usr/bin/nova-dhcpbridge
dhcpbridge_flagfile =
/etc/nova/nova.conf
dmz_cidr =
dmz_mask = 255.255.255.0
dmz_net = 10.0.0.0
dns_server =
dns_update_periodic_interval = -1
dnsmasq_config_file =
ebtables_exec_attempts = 3
ebtables_retry_interval = 1.0
ec2_listen = 0.0.0.0
ec2_listen_port = 8773
ec2_private_dns_show_ip = False
ec2_strict_validation = True
ec2_timestamp_expiry = 300
ec2_workers = 2
enable_new_services = True
enabled_apis =
ec2
metadata
osapi_compute
enabled_ssl_apis =
fake_call = False
fake_network = False
fatal_deprecations = False
fatal_exception_format_errors = False
firewall_driver = nova.virt.libvirt.firewall.IptablesFirewallDriver
fixed_ip_disassociate_timeout = 600
fixed_range_v6 = fd00::/48
flat_injected = False
flat_interface = p1p1
flat_network_bridge = br100
flat_network_dns = 8.8.4.4
floating_ip_dns_manager = nova.network.noop_dns_driver.NoopDNSDriver
force_config_drive = always
force_dhcp_release = True
force_raw_images = True
force_snat_range =
forward_bridge_interface =
all
gateway = None
gateway_v6 = None
heal_instance_info_cache_interval = 60
host = mustard.gsslab.fab.redhat.com
image_cache_manager_interval = 2400
image_cache_subdirectory_name = _base
injected_network_template = /home/berrange/src/cloud/nova/nova/virt/interfaces.template
instance_build_timeout = 0
instance_delete_interval = 300
instance_dns_domain =
instance_dns_manager = nova.network.noop_dns_driver.NoopDNSDriver
instance_format = [instance: %(uuid)s]
instance_name_template = instance-%08x
instance_usage_audit = False
instance_usage_audit_period = month
instance_uuid_format = [instance: %(uuid)s]
instances_path = /home/berrange/src/cloud/data/nova/instances
internal_service_availability_zone = internal
iptables_bottom_regex =
iptables_drop_action = DROP
iptables_top_regex =
ipv6_backend = rfc2462
key_file = private/cakey.pem
keys_path = /home/berrange/src/cloud/data/nova/keys
keystone_ec2_insecure = False
keystone_ec2_url = http://10.33.8.112:5000/v2.0/ec2tokens
l3_lib = nova.network.l3.LinuxNetL3
linuxnet_interface_driver = nova.network.linux_net.LinuxBridgeInterfaceDriver
linuxnet_ovs_integration_bridge = br-int
live_migration_retry_count = 30
lockout_attempts = 5
lockout_minutes = 15
lockout_window = 15
log-config-append = None
log-date-format = %Y-%m-%d %H:%M:%S
log-dir = None
log-file = None
log-format = None
logging_context_format_string = %(asctime)s.%(msecs)03d %(color)s%(levelname)s %(name)s [%(request_id)s %(user_name)s %(project_name)s%(color)s] %(instance)s%(color)s%(message)s
logging_debug_format_suffix = from (pid=%(process)d) %(funcName)s %(pathname)s:%(lineno)d
logging_default_format_string = %(asctime)s.%(msecs)03d %(color)s%(levelname)s %(name)s [-%(color)s] %(instance)s%(color)s%(message)s
logging_exception_prefix = %(color)s%(asctime)s.%(msecs)03d TRACE %(name)s %(instance)s
max_age = 0
max_concurrent_builds = 10
max_header_line = 16384
max_local_block_devices = 3
maximum_instance_delete_attempts = 5
memcached_servers = None
metadata_host = 10.33.8.112
metadata_listen = 0.0.0.0
metadata_listen_port = 8775
metadata_manager = nova.api.manager.MetadataManager
metadata_port = 8775
metadata_workers = 2
migrate_max_retries = -1
mkisofs_cmd = genisoimage
monkey_patch = False
monkey_patch_modules =
nova.api.ec2.cloud:nova.notifications.notify_decorator
nova.compute.api:nova.notifications.notify_decorator
multi_host = True
multi_instance_display_name_template = %(name)s-%(count)d
my_block_storage_ip = 10.33.8.112
my_ip = 10.33.8.112
network_allocate_retries = 0
network_api_class = nova.network.api.API
network_device_mtu = None
network_driver = nova.network.linux_net
network_manager = nova.network.manager.FlatDHCPManager
network_size = 256
network_topic = network
networks_path = /home/berrange/src/cloud/data/nova/networks
non_inheritable_image_properties =
bittorrent
cache_in_nova
notification_driver =
notification_topics =
notifications
notify_api_faults = False
notify_on_state_change = None
novncproxy_base_url = http://10.33.8.112:6080/vnc_auto.html
null_kernel = nokernel
num_networks = 1
osapi_compute_listen = 0.0.0.0
osapi_compute_listen_port = 8774
osapi_compute_workers = 2
ovs_vsctl_timeout = 120
password_length = 12
pci_alias =
pci_passthrough_whitelist =
periodic_enable = True
periodic_fuzzy_delay = 60
policy_default_rule = default
policy_dirs =
policy.d
policy_file = policy.json
preallocate_images = none
project_cert_subject = /C=US/ST=California/O=OpenStack/OU=NovaDev/CN=project-ca-%.16s-%s
public_interface = br100
publish_errors = False
pybasedir = /home/berrange/src/cloud/nova
qpid_heartbeat = 60
qpid_hostname = 10.33.8.112
qpid_hosts =
10.33.8.112:5672
qpid_password = ***
qpid_port = 5672
qpid_protocol = tcp
qpid_receiver_capacity = 1
qpid_sasl_mechanisms =
qpid_tcp_nodelay = True
qpid_topology_version = 1
qpid_username =
quota_cores = 20
quota_driver = nova.quota.DbQuotaDriver
quota_fixed_ips = -1
quota_floating_ips = 10
quota_injected_file_content_bytes = 10240
quota_injected_file_path_length = 255
quota_injected_files = 5
quota_instances = 10
quota_key_pairs = 100
quota_metadata_items = 128
quota_ram = 51200
quota_security_group_rules = 20
quota_security_groups = 10
quota_server_group_members = 10
quota_server_groups = 10
reboot_timeout = 0
reclaim_instance_interval = 0
remove_unused_base_images = True
remove_unused_original_minimum_age_seconds = 86400
report_interval = 10
rescue_timeout = 0
reservation_expire = 86400
reserved_host_disk_mb = 0
reserved_host_memory_mb = 512
resize_confirm_window = 0
resize_fs_using_block_device = False
resume_guests_state_on_host_boot = False
rootwrap_config = /etc/nova/rootwrap.conf
routing_source_ip = 10.33.8.112
rpc_backend = qpid
rpc_conn_pool_size = 30
rpc_response_timeout = 60
rpc_thread_pool_size = 64
run_external_periodic_tasks = True
running_deleted_instance_action = reap
running_deleted_instance_poll_interval = 1800
running_deleted_instance_timeout = 0
scheduler_available_filters =
nova.scheduler.filters.all_filters
scheduler_default_filters =
AvailabilityZoneFilter
ComputeCapabilitiesFilter
ComputeFilter
ImagePropertiesFilter
RamFilter
RetryFilter
ServerGroupAffinityFilter
ServerGroupAntiAffinityFilter
scheduler_manager = nova.scheduler.manager.SchedulerManager
scheduler_max_attempts = 3
scheduler_topic = scheduler
scheduler_weight_classes =
nova.scheduler.weights.all_weighers
security_group_api = nova
send_arp_for_ha = True
send_arp_for_ha_count = 3
service_down_time = 60
servicegroup_driver = db
share_dhcp_address = False
shelved_offload_time = 0
shelved_poll_interval = 3600
shutdown_timeout = 60
snapshot_name_template = snapshot-%s
ssl_ca_file = None
ssl_cert_file = None
ssl_key_file = None
state_path = /home/berrange/src/cloud/data/nova
sync_power_state_interval = 600
syslog-log-facility = LOG_USER
tcp_keepidle = 600
teardown_unused_network_gateway = False
tempdir = None
transport_url = None
until_refresh = 0
update_dns_entries = False
use-syslog = False
use-syslog-rfc-format = False
use_cow_images = True
use_forwarded_for = False
use_ipv6 = False
use_network_dns_servers = False
use_project_ca = False
use_single_default_gateway = False
use_stderr = True
user_cert_subject = /C=US/ST=California/O=OpenStack/OU=NovaDev/CN=%.16s-%.16s-%s
vcpu_pin_set = None
vendordata_driver = nova.api.metadata.vendordata_json.JsonFileVendorData
verbose = True
vif_plugging_is_fatal = True
vif_plugging_timeout = 300
virt_mkfs =
vlan_interface =
vlan_start = 100
vnc_enabled = True
vnc_keymap = en-us
vncserver_listen = 127.0.0.1
vncserver_proxyclient_address = 127.0.0.1
volume_api_class = nova.volume.cinder.API
volume_usage_poll_interval = 0
vpn_flavor = m1.tiny
vpn_image_id = 0
vpn_ip = 10.33.8.112
vpn_key_suffix = -vpn
vpn_start = 1000
wsgi_default_pool_size = 1000
wsgi_keep_alive = True
wsgi_log_format = %(client_ip)s "%(request_line)s" status: %(status_code)s len: %(body_length)s time: %(wall_seconds).7f
xvpvncproxy_base_url = http://10.33.8.112:6081/console
ephemeral_storage_encryption:
cipher = aes-xts-plain64
enabled = False
key_size = 512
glance:
allowed_direct_url_schemes =
api_insecure = False
api_servers =
http://10.33.8.112:9292
host = 10.33.8.112
num_retries = 0
port = 9292
protocol = http
guestfs:
debug = False
keymgr:
api_class = nova.keymgr.conf_key_mgr.ConfKeyManager
libvirt:
block_migration_flag = VIR_MIGRATE_UNDEFINE_SOURCE, VIR_MIGRATE_PEER2PEER, VIR_MIGRATE_LIVE, VIR_MIGRATE_TUNNELLED, VIR_MIGRATE_NON_SHARED_INC
checksum_base_images = False
checksum_interval_seconds = 3600
connection_uri =
cpu_mode = none
cpu_model = None
disk_cachemodes =
disk_prefix = None
gid_maps =
glusterfs_mount_point_base = /home/berrange/src/cloud/data/nova/mnt
hw_disk_discard = None
hw_machine_type = None
image_info_filename_pattern = /home/berrange/src/cloud/data/nova/instances/_base/%(image)s.info
images_rbd_ceph_conf =
images_rbd_pool = rbd
images_type = default
images_volume_group = None
inject_key = False
inject_partition = -2
inject_password = False
iscsi_iface = None
iscsi_use_multipath = False
iser_use_multipath = False
live_migration_bandwidth = 0
live_migration_flag = VIR_MIGRATE_UNDEFINE_SOURCE, VIR_MIGRATE_PEER2PEER, VIR_MIGRATE_LIVE, VIR_MIGRATE_TUNNELLED
live_migration_uri = qemu+ssh://berrange@%s/system
mem_stats_period_seconds = 10
nfs_mount_options = None
nfs_mount_point_base = /home/berrange/src/cloud/data/nova/mnt
num_aoe_discover_tries = 3
num_iscsi_scan_tries = 5
num_iser_scan_tries = 5
qemu_allowed_storage_drivers =
quobyte_client_cfg = None
quobyte_mount_point_base = /home/berrange/src/cloud/data/nova/mnt
rbd_secret_uuid = None
rbd_user = None
remove_unused_kernels = False
remove_unused_resized_minimum_age_seconds = 3600
rescue_image_id = None
rescue_kernel_id = None
rescue_ramdisk_id = None
rng_dev_path = None
scality_sofs_config = None
scality_sofs_mount_point = /home/berrange/src/cloud/data/nova/scality
smbfs_mount_options =
smbfs_mount_point_base = /home/berrange/src/cloud/data/nova/mnt
snapshot_compression = False
snapshot_image_format = None
snapshots_directory = /home/berrange/src/cloud/data/nova/instances/snapshots
sparse_logical_volumes = False
sysinfo_serial = auto
uid_maps =
use_usb_tablet = False
use_virtio_for_bridges = True
virt_type = kvm
volume_clear = zero
volume_clear_size = 0
volume_drivers =
aoe=nova.virt.libvirt.volume.LibvirtAOEVolumeDriver
fake=nova.virt.libvirt.volume.LibvirtFakeVolumeDriver
fibre_channel=nova.virt.libvirt.volume.LibvirtFibreChannelVolumeDriver
glusterfs=nova.virt.libvirt.volume.LibvirtGlusterfsVolumeDriver
gpfs=nova.virt.libvirt.volume.LibvirtGPFSVolumeDriver
iscsi=nova.virt.libvirt.volume.LibvirtISCSIVolumeDriver
iser=nova.virt.libvirt.volume.LibvirtISERVolumeDriver
local=nova.virt.libvirt.volume.LibvirtVolumeDriver
nfs=nova.virt.libvirt.volume.LibvirtNFSVolumeDriver
quobyte=nova.virt.libvirt.volume.LibvirtQuobyteVolumeDriver
rbd=nova.virt.libvirt.volume.LibvirtNetVolumeDriver
scality=nova.virt.libvirt.volume.LibvirtScalityVolumeDriver
sheepdog=nova.virt.libvirt.volume.LibvirtNetVolumeDriver
smbfs=nova.virt.libvirt.volume.LibvirtSMBFSVolumeDriver
wait_soft_reboot_seconds = 120
xen_hvmloader_path = /usr/lib/xen/boot/hvmloader
osapi_v3:
enabled = True
extensions_blacklist =
extensions_whitelist =
oslo_concurrency:
disable_process_locking = False
lock_path = /home/berrange/src/cloud/data/nova
rdp:
enabled = False
html5_proxy_base_url = http://127.0.0.1:6083/
remote_debug:
host = None
port = None
serial_console:
base_url = ws://127.0.0.1:6083/
enabled = False
listen = 127.0.0.1
port_range = 10000:20000
proxyclient_address = 127.0.0.1
spice:
agent_enabled = True
enabled = False
html5proxy_base_url = http://10.33.8.112:6082/spice_auto.html
keymap = en-us
server_listen = 127.0.0.1
server_proxyclient_address = 127.0.0.1
ssl:
ca_file = None
cert_file = None
key_file = None
upgrade_levels:
baseapi = None
cells = None
compute = None
conductor = None
console = None
consoleauth = None
network = None
scheduler = None
workarounds:
disable_libvirt_livesnapshot = True
disable_rootwrap = False
When developing on OpenStack, it is standard practice for the unit test suites to be run in a python virtualenv. With the Nova project at least, and I suspect most others too, setting up the virtualenv takes a significant amount of time as there are many packages to pull down from PyPI, quite a few of which need compilation too. Any time the local requirements.txt or test-requirements.txt files change it is necessary to the rebuild the virtualenv. This rebuild is an all-or-nothing kind of task, so can be a significant time sink, particularly if you frequently jump between different code branches.
At the OpenStack design summit in Paris, Joe Gordon showed Matt Booth how to setup devpi and wheel to provide a cache of the packages that make up the virtualenv. Not only does it avoid the need to repeatedly download the same packages from pypi each time, but it also avoids the compilation step, since the cache is storing the final installed pieces for each python module. The end result is that it takes 20-30 seconds or less to rebuild a virtualenv instead of many minutes.
After a few painful waits for virtualenvs today, I decided to set it up too I don’t like installing non-packaged software as root on my machines, so what follows is all done as a regular user account. The first step is to pull down the devpi and wheel packages from pypi, telling pip to install them in under $HOME/.local
# pip install --user devpi
# pip install --user wheel
Since we’re using a custom install location, it necessary to update your $HOME/.bashrc file with new $PATH and $PYTHONPATH environment variables and then source the .bashrc file
# cat >> $HOME/.bashrc <<EOF
export PATH=\$PATH:$HOME/.local/bin
export PYTHONPATH=$HOME/.local/lib/python2.7/site-packages
EOF
# . $HOME/.bashrc
The devpi package provides a local server that will be used for downloads instead of directly accessing pypi.python.org, so this must be started
# devpi-server --start
Both devpi and wheel integrate with pip, so the next setup task is to modify the pip configuration file
# cat >> $HOME/.pip/pip.conf <<EOF
[global]
index-url = http://localhost:3141/root/pypi/+simple/
wheel-dir = /home/berrange/.pip/wheelhouse
find-links = /home/berrange/.pip/wheelhouse
EOF
We’re pretty much done at this point – all that is left is to prime the cache with the all the packages that Nova wants to use
# cd $HOME/src/cloud/nova
# pip wheel -r requirements.txt
# pip wheel -r test-requirements.txt
Now if you run any command that would build a Nova virtualenv, you should notice it is massively faster
# tox -e py27
# ./run_tests.sh -V
That is basically all there is to it. Blow away the virtualenv directories at any time and they’ll be repopulated from the cache. If the requirements.txt is updated with new deps re-running the ‘pip wheel’ command above will update the cache to hold the new bits.
That was all incredibly easy and so I’d highly recommend devs on any non-trivially sized python project make use of it. Thanks to Joe Gordon for the pointing this out at the summit !
The previous blog post looked at the history of libvirt APIs for spawning processes, up to the current day where there is a single virCommand object + APIs for spawning processes in a very flexible manner. This blog post will now look at the key features of this API and how it is used in practice.
Example usage
Before going into the dry details, lets consider a couple of real world examples where libvirt uses these APIs.
“system” replacement
As a first example, the “virNodeSuspendSetNodeWakeup” method is a place where libvirt might have traditionally used the ‘system’ call.
The goal is to suspend the host, setting a pre-defined wakeup alarm, for which libvirt needs to run the ‘rtcwake’ command. The wakeup time is provided to the API in terms of a unsigned long long which needs to be converted to a string.
If attempting this with the ‘system’ call the code might look like this:
static int virNodeSuspendSetNodeWakeup(unsigned long long alarmTime)
{
char *setAlarmCmd;
int ret = -1;
if (asprintf(&setAlarmCmd, "rtcwake -m no -s %lld", alarmTime) < 0)
goto cleanup;
if (system(setAlarmCmd) < 0)
goto cleanup;
ret = 0;
cleanup:
free(setAlarmCmd);
return ret;
}
Now consider what this would look like when using the virCommand APIs:
static int virNodeSuspendSetNodeWakeup(unsigned long long alarmTime)
{
virCommandPtr setAlarmCmd;
int ret = -1;
setAlarmCmd = virCommandNewArgList("rtcwake", "-m", "no", "-s", NULL);
virCommandAddArgFormat(setAlarmCmd, "%lld", alarmTime);
if (virCommandRun(setAlarmCmd, NULL) < 0)
goto cleanup;
ret = 0;
cleanup:
virCommandFree(setAlarmCmd);
return ret;
}
The difference in code complexity is negligible, but the difference in the quality of the implementation is significant.
“popen” replacement
As a second example, the “virStorageBackendIQNFound” method is a place where libvirt might have traditionally used the ‘popen’ call.
The goal this time is to run the iscsiadm command with a number of arguments and parse its stdout to look for a particular iSCSI target.
First consider what this might look like when using ‘popen’
static int virStorageBackendIQNFound(const char *initiatoriqn,
char **ifacename)
{
int ret = -1;
FILE *fp = NULL;
int fd = -1;
char line[4096]
if ((fp = popen("iscsiadm --mode iface")) == NULL)
goto cleanup;
while (fgets(line, 4096, fp) != NULL) {
...analyse line for a match...
}
ret = 0;
cleanup:
pclose(fp);
close(fd);
virCommandFree(cmd);
return ret;
}
Now consider the re-write to use virCommand APIs
static int virStorageBackendIQNFound(const char *initiatoriqn,
char **ifacename)
{
int ret = -1;
FILE *fp = NULL;
int fd = -1;
char line[4096]
virCommandPtr cmd = virCommandNewArgList("iscsiadm", "--mode", "iface", NULL);
virCommandSetOutputFD(cmd, &fd);
if (virCommandRunAsync(cmd, NULL) < 0)
goto cleanup;
if ((fp = fdopen(fd, "r")) == NULL)
goto cleanup;
while (fgets(line, 4096, fp) != NULL) {
...analyse line for a match...
}
if (virCommandWait(cmd, NULL) < 0)
goto cleanup;
ret = 0;
cleanup:
fclose(fp);
close(fd);
virCommandFree(cmd);
return ret;
}
There is a little more work todo for virCommand in terms of initial setup in this example. Technically the call to ‘virCommandWait’ could have been omitted here, since we don’t care about the exit status, but it is good practice to included it. If we had extra dynamic arguments to be provided to ‘iscsiadm’ that needed string formatting the two examples would have been nearer parity in terms of complexity. Even with the slightly longer code for virCommand, the result is a clear win from the quality POV avoiding the many flaws of popen’s implementation.
Detailed API examination
Now that the two examples have given a taste of what the virCommand APIs can do to replace popen/system, lets consider the full set of features exposed. After this it should be clear that the flexibility of the virCommand means there is never any need to delve into fork+exec anymore, let alone popen/system.
Constructing the command arguments
Probably the first task when spawning a command is actually construct the array of arguments and environment variables. In simple cases this can be done immediately when allocating the new virCommad object instance, for example using var-args
virCommandPtr cmd = virCommandNewArgList("touch", "/tmp/foo", NULL);
there is no need to check the return value of virCommandNew* for NULL. The later virCommandRun() API will look for a NULL pointer and report the OOM error at that point instead. The same is true for all error reporting in these APIs – virCommandRun is generally the only place where an error check is needed. This simplification in error handling is a major contributor to making this APIs hard to mis-use in calling code and thus minimizing errors.
Sometimes the list of arguments is not so simple that it can be initialized in one go via var-args. To deal with this it is possible to add arguments to an existing constructed command in a variety of ways
virCommandAddArgFormat(cmd, "--size=%d", 1025);
virCommandAddArgPair(cmd, "--user", "fred");
virCommandAddArgList(cmd, "some", "extra", "args", NULL);
This is handy because for complex command lines (eg those used with QEMU) it allows construction of the virCommand to be split up across multiple functions, each adding their own piece of the command line.
Setting up the environment
By default a process spawned will inherit the full environment of the parent process (almost always libvirtd in libvirt code). With things like QEMU though libvirt wants to be in complete control of the environment it runs under, so it will filter the environment to a subset of names. There are a couple of env variables that are always desired to pass down LD_PRELOAD, LD_LIBRARY_PATH, PATH, USER, HOME, LOGNAME & TMPDIR. If this set is desired there is a convenient method to request passthrough of this set
virCommandAddEnvPassCommand(cmd);
Additional environment variables can be set for passthrough from libvirtd. When passing through environment variables libvirt requires an explicit decision on whether the env variable is safe to pass when running setuid. If an env variable is considered unsafe for a setuid application, there is the option of passing a default value to substitute. The “PATH” variable is unsafe to pass when setuid, and should be set to a known safe value when running setuid:
virCommandAddEnvPassBlockSUID(cmd, "PATH", "/bin:/usr/bin");
The “LD_LIBRARY_PATH” variable is also unsafe when running setuid and should simply be dropped from the environment entirely:
virCommandAddEnvPassBlockSUID(cmd, "LD_LIBRARY_PATH", NULL);
Finally the “LOGNAME” is fine to allow even when setuid so can be left unchanged
virCommandAddEnvPassAllowSUID(cmd, "LOGNAME");
It is not always sufficient to just passthrough existing environment variables, so there are of course APIs to set them directly
virCommandAddEnvPair(cmd, "LOGNAME", "fred");
virCommandAddEnvFormat(cmd, "LOGNAME=%s", fred);
virCommandAddEnvString(cmd, "LOGNAME=fred");
Setting security attributes
Under UNIX a program will inherit process limits, umask and working directory from the parent. It is thus desirable to be able to override this, for example:
virCommandSetMaxFiles(cmd, 65536);
Along a similar vein the child’s umask can also be set
virCommandSetUmask(cmd, 0007);
If the current process’ working directory is unknown, it is a good idea to force an explicit working directory:
virCommandSetWorkingDirectory(cmd, "/");
It may sometimes be desirable to control what capabilities bits a child process has, to override the default behaviour. In such cases the command would to be initialized with the empty set and then the desired bits whitelisted.
virCommandClearCaps(cmd);
virCommandAllowCap(cmd, CAP_NET_RAW);
Finally when interacting with mandatory access control systems like SELinux or AppArmour it is possible to configure an explicit label for the child
virCommandSetSELinuxLabel(cmd, "system_u:system_r:svirt_t:s0:c135,c275");
virCommandSetAppArmorProfile(cmd, "2cb0e828-e6f6-40d1-b0f5-c50cdf34f5c9");
Interacting with stdio
A common requirement when spawning processes is to be able to interact with the child’s stdio in some manner. By default with the virCommand APIs, a process will get its stdin, stdout & stderr connected to /dev/null. For stdin there is a choice of feeding it a fixed length string, or connecting it up to the read end of an existing file descriptor, typically a pipe
virCommandSetInputBuffer(cmd, "Feed me brains");
virCommandSetInputFD(cmd, pipefd);
There are a similar pair of choices for receiving the stdout/stderr from the child. It is possible to supply a pointer to a ‘char *’ which will be filled with the child’s output upon exit. Alternatively a pointer to an ‘int’ can be provided, which can either specify an existing file descriptor, or if ‘-1’ a new anonymous pipe will be created.
char *child_out, *child_err;
virCommandSetOutputBuffer(cmd, &child_out);
virCommandSetErrorBuffer(cmd, &child_err);
int child_out -1, child_err = -1;
virCommandSetOutputFD(cmd, &child_out);
virCommandSetOutputFD(cmd, &child_err);
Passing file descriptors
Aside from any associated with stdio, all file descriptors will be closed when the child process is launched. This is generally a good thing since it prevents any leakage of file descriptors to the child. Such leakage can be a security flaw, and unless using glibc extensions to POSIX, it is not possible to avoid the race condition with setting O_CLOEXEC, so an explicit mass close is a very desirable approach. There can be times when it is is necessary to pass other arbitrary file descriptors to a child process. When passing a file descriptor it may also be desirable to close it in the parent process.
virCommandPassFD(cmd, 8, 0);
virCommandPassFD(cmd, 8, VIR_COMMAND_PASS_FD_CLOSE_PARENT);
Pre-exec callback hooks
Despite its wide range of features, there are times when the virCommand API is not sufficient for the job. In these cases there is the ability to request that a callback function be invoked immediately before exec’ing the child binary. This allows the caller to do arbitrary extra work, though of course bearing in mind POSIX’s rules about which functions are safe to use between fork+exec in a threaded application.
int my_hook(void *data)
{
if (sometask(data) < 0)
return -1;
return 0;
}
virCommandSetPreExecHook(cmd, my_hook, "thefilename");
Executing the command
Everything until this point has been about setting up the command args and the constraints under which it will execute. None of the APIs shown so far require any kind of error checking of return values. Only now that it is time to execute the command will errors be reported and checked by the caller. The simplest way to execute is to use ‘virCommandRun’ which will block until the command finishes running and report the exit status
int status;
if (virCommandRun(cmd, &status) < 0) {
virCommandFree(cmd);
return -1;
}
virCommandFree(cmd);
It is possible to leave the ‘status’ arg as NULL in which case the API will turn any non-zero exit status into a fatal error. If the intention is to interact with the command via one or more file descriptors connected to stdio, then a slightly more flexible ‘virCommandRunAsync’ API is required. This call will only block until the process is actually running. The parent can then interact with it and when ready call ‘virCommandWait’.
int status;
pid_t child;
if (virCommandRunAsync(cmd, &child) < 0) {
virCommandFree(cmd);
return -1;
}
...interact with child via stdio or other means...
if (virCommandWait(cmd, &status) < 0) {
virCommandFree(cmd);
return -1;
}
virCommandFree(cmd);
If something goes wrong during interaction, it is possible to terminate the process with prejudice by using ‘virCommandAbort’ instead of ‘virCommandWait’.
Synchronizing with the child
Normally, once a child has fork’d off, the child & parent will continue execution in parallel, with the parent having no idea at which point the final exec() will have been performed. There can be cases where the parent needs to do some work in between the fork and exec. A pre-exec hook can often be used for this, but the work needs to take place in the parent process another solution is required. To deal with this it is possible to request a handshake take place with the child process. Before the child exec’s its binary, it will notify the parent process that is wants to handshake and wait for a reply. The parent process meanwhile will wait to be notify, then do its work and finally reply to the child again
virCommandRequireHandshake(cmd);
if (virCommandRunAsync(cmd) < 0)
return -1;
virCommandHandshakeWait(cmd);
...do setup work...
virCommandHandshakeNotify(cmd);
Simplified command execution
The examples above are very powerful, but in the simplest use cases it is possible to combine the virCommandNew + virCommandRun + virCommandFree calls into a single API call
const char *args[] = { "/bin/program", "arg1", "arg2", NULL };
if (virRun(args, NULL) < 0)
return -1;
This is pretty much equivalent to ‘system’ in terms of complexity, but much safer as it avoids the shell and many other problems mentioned previously.
Integration with unit tests
One of the particularly interesting features of the virCommand APIs is the ability to do unit testing of code that otherwise spawns external commands. The test suite can define a callback that will be invoked any time an attempt is made to run a command. This callback can analyse stdin string, fill in stdout/stderr strings and set the exit status. This is sufficient to avoid the need to run the real command in the context of unit tests in most cases.
static void testCommandCallback(const char *const*args,
const char *const*env,
const char *input,
char **output,
char **error,
int *status,
void *opaque)
{
....fake the exit status and fill in **output or **error...
}
virCommandSetDryRun(NULL, testCommandCallback, NULL);
The End
That completes our whirlwind tour of libvirts APIs for spawning child processes. It should be clear that a lot of thought & effort has gone into designing a set of APIs that maximize safety without compromising on ease of use. There can really be no excuse for using either the popen or system calls for spawning programs & thus leaving yourself vulnerable to flaws like shellshock. The libvirt code described in this post is all available under the terms of the LGPLv2+ should anyone wish to pull out & adapt the virCommand APIs for their own programs. I look forward to the day when it is possible to use a Linux system with no reliance on shell by any program. Shell should be exclusively for use by interactive login sessions and administrator local scripting work, not a part of applications where it only ever leads to misery & insecurity.