What fields should be used for reporting shared memory?

[Steve Grubb]

On Monday, March 20, 2017 7:36:14 AM EDT Martin Kletzander wrote:
> On Thu, Mar 16, 2017 at 09:04:52PM -0400, Steve Grubb wrote:
> >Hello,
> >
> >I apologize for the delay.
> >
> >On Tuesday, March 14, 2017 7:42:27 AM EDT Martin Kletzander wrote:
> >> I am going through the fields in the dictionary and I can't find any
> >> name to use for the following scenario.
> >> 
> >> We (libvirt) are running virtual machines and there's a thing nowadays,
> >> that people like to use, called ivshmem (Inter-VM SHared MEMory).  From
> >> host's point of view this is just a shared memory region accessed by
> >> multiple VMs (and possibly to host as well).  The machine maps the
> >> shared memory given a name (e.g. name "asdf" results in /dev/shm/asdf to
> >> be mapped) *or* it can communicate with a server over UNIX socket and
> >> that server handles interrupts and also tells the client which shared
> >> memory region to map.
> >
> >If both of these result in a path, then I think we want to log it as a
> >resource event.
> 
> Yes, and they both are resources in its sense. So you are talking
> particularly about the resrc= field?  Should that also have category and
> class or anything else set?  Or do you mean we report the path in the
> resrc= field?

No, I mean we would want the path to the memory in a VIRT_RESOURCE event. :-)  
How about something like this:

type=VIRT_RESOURCE msg=audit(1488441043.591:2977): pid=25464 uid=0 
auid=4294967295 ses=4294967295 subj=system_u:system_r:virtd_t:s0-s0:c0.c1023 
msg='virt=kvm resrc=shmem reason=start vm="rhel7.3" uuid=a7708061-
faa0-42ce-897a-e92fb75fcf1d size=4194304 path="/dev/shm/my_shmem1" exe="/usr/
sbin/libvirtd" hostname=? addr=? terminal=? res=success'

Having the full path would make it more normal when reporting on files in use.


> >> Talking about information we have; in server-less
> >> setup it's the shared memory region that is shared, in the server
> >> scenario it is the socket.  That's information we can output.
> >
> >Above you mentioned that the server communicates which region to map. Can
> >you explain what that means?
> 
> The server sends a file descriptor to the VM over the socket, details
> can be found here:
> 
> http://git.qemu-project.org/?p=qemu.git;a=blob;f=docs/specs/ivshmem-spec.txt
> #l151

This one is harder. What we really want to know is the size information. But 
libvirtd doesn't have it I assume. That makes it sound like ivshmem should log 
it, but it probably doesn't know the reason, vm name, or uuid or anything 
else. So, this is probably not good.

I guess about all that you can say is that a ivshmem-socket is being assigned. 
I guess let's do it like this:

type=VIRT_RESOURCE msg=audit(1488441043.591:2977): pid=25464 uid=0 
auid=4294967295 ses=4294967295 subj=system_u:system_r:virtd_t:s0-s0:c0.c1023 
msg='virt=kvm resrc=ivshmem-socket reason=start vm="rhel7.3" uuid=a7708061-
faa0-42ce-897a-e92fb75fcf1d ivshmem="my_shmem2" exe="/usr/sbin/libvirtd" 
hostname=? addr=? terminal=? res=success'

-Steve

> >> So my question is, when starting a domain or hot-(un)plugging, what
> >> naming should we use for this kind of device and what are the things
> >> that we should describe about it?  Basically, how would you like the
> >> message to look?
> >
> >We need a record recording what is getting assigned to the VM. In the case
> >of the /dev/shm, you can record that as a path which must be escaped. In
> >the case of the server, I think we still need to understand what is
> >happening. Just recording a socket number or path is not terribly useful
> >in reconstructing the resources given to the VM.
> >
> >Audit events have to tell a story. There is a subect, object, action, and
> >results. It kind of needs to be a sentence. "libvirtd successfully assigned
> >____ to vm-name."
> >
> >-Steve
> >
> >> Thanks in advance for any info.
> >> 
> >> Have a nice day,
> >> Martin