On 31/08/12 18:09, Daniel P. Berrange wrote:
On Fri, Aug 31, 2012 at 03:23:18PM +0300, NoxDaFox wrote:
Greetings,
I am working on a platform for analysis automation.
I need to run several Virtual Environments concurrently and record
information about their behavior.
I wrote some months ago about the capability of reading the Memory
during the Environment's execution (in paused state).
What do I need is the complete linear memory image, byte per byte,
nothing special; I will give this output to tools and parsers like
Volatility to get the value from it.
If you want the complete memory image, perhaps you can just run the
virDomainCoreDump() command, with the VIR_DUMP_MEMORY_ONLY flag
(though this flag only works on very recent QEMU)
I'm working on Debian Wheezy, the flag you're talking about is in
libvirt 0.9.13, it's in experimental now, do you know if it's going to
be included into the next stable release?
I'm using libvirt 0.9.13 and QEMU 1.1.1 (from experimental as well) and
the result is an error which tells the feature is not supported by QEMU,
do I need an even more recent version?
I looked around and the only way to get the memory in such a way is
using the QEMU monitor command `pmemsave`.
I am using libvirt through its Python bindings and the
virDomainQemuMonitorCommand seems not to be exposed by the API so, as
suggested in some mails I read into the mailig list, I switched to
virDomainMemoryPeek.
Using this function keeps up to 14-16 seconds to read 512Mb of memory
with the 64Kb limitation and 2-3 seconds with the 1Mb one; but the
most annoying thing is that I can't run several environment
concurrently as the function keeps failing.
FYI, the virDomainMemoryPeek command was not really designed with
scalability in mind, in particular not really intended for dumping
the entire of guest memory. Its use case was tools like the virt-dmesg
command, where you just want to peek at a handful of small memory
regions.
What I realized is a simple Python iterator that allows to iterate
through Disk and Memory with chunk of 64K or 1M depending on the libvirt
version.
The users may have the need to read the entire memory before finding
what they're looking for.
Do you think would be feasible to rework on this command allowing more
scalability at least?
Here's the typical output:
File "/home/nox/workspace/NOX/src/NOX/hooks.py", line 134, in trigger
hook.trigger(event)
File "/home/nox/workspace/NOX/src/NOX/hooks.py", line 33, in trigger
self.handlers[event]()
File "/home/nox/workspace/NOX/hooks/volatility.py", line 81, in memory_dump
for block in Memory(self.ctx):
File "/home/see/workspace/NOX/src/NOX/lib/libtools.py", line 179, in next
libvirt.VIR_MEMORY_PHYSICAL)
File "/usr/lib/python2.7/dist-packages/libvirt.py", line 1759, in memoryPeek
ret = libvirtmod.virDomainMemoryPeek(self._o, start, size, flags)
SystemError: error return without exception set
Hmm, that's a peculiar message to see - I can't find anywhere in the
libvirt code that uses that particular messages, so I'm not sure what
has gone wrong here.
Is a Python message, it's triggered once a C method returns NULL.
I can't run more than 3 environments concurrently on a Xeon Quad with
8Gb of memory.
I guess the RPC reply goes in timeout because the system is under
heavy load but I'm not sure as the error output is quite obscure.
Is there any solution to this issue? Is it possible to raise the RPC
reply timeout value so that, even if slowly, I eventually get the
memory dump?
For the memory peek API, we invoked a QEMU monitor command - we should
not timeout on this at all, unless you are trying to invoke other
monitor commands against the same QEMU process concurrently
So there's some other problem; I run several tests and seems to happen
randomly, is not depending which block of memory is reading.
It is enough to read memory from 3 different running guests at the same
time to see this issue.
If through virsh I use the QEMU `pmemsave` command, I get the memory
dump in less than one second; is there any way to obtain the same
performance?
If virsh works properly, then this suggests the problem is somewhere
in the python code, either libvirt's python binding, or your apps
usage.
The virsh monitor command uses an unexposed API method:
virDomainQemuMonitorCommand. This method is not available in the Python
APIs neither is documented in libvirt documentation. I assume is for
internal use only.
I can use this strategy as a workaround, but spawning a virsh process
just for run this command while I can access to such resources as the
connection to the Hypervisor and the Domain doesn't seem a clever
solution to me.
NoxDaFox
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