Relax the restriction that the hash table key must be a string
by allowing an arbitrary hash code generator + comparison func
to be provided

* util/hash.c, util/hash.h: Allow any pointer as a key
* internal.h: Include stdbool.h as standard.
* conf/domain_conf.c, conf/domain_conf.c,
  conf/nwfilter_params.c, nwfilter/nwfilter_gentech_driver.c,
  nwfilter/nwfilter_gentech_driver.h, nwfilter/nwfilter_learnipaddr.c,
  qemu/qemu_command.c, qemu/qemu_driver.c,
  qemu/qemu_process.c, uml/uml_driver.c,
  xen/xm_internal.c: s/char */void */ in hash callbacks

When run non-root the nwfilter driver logs error messages about
being unable to find iptables/ebtables commands (they are in
/sbin which isn't in $PATH). The nwfilter driver can't ever work
as non-root, so simply skip it entirely thus avoiding the error
messages

* src/conf/nwfilter_conf.h, src/nwfilter/nwfilter_driver.c,
  src/nwfilter/nwfilter_gentech_driver.c,
  src/nwfilter/nwfilter_gentech_driver.h: Pass 'bool privileged'
  flag down to final driver impl
* src/nwfilter/nwfilter_ebiptables_driver.c: Skip initialization
  if not privileged

Following Daniel Berrange's multiple helpful suggestions for improving
this patch and introducing another driver interface, I now wrote the
below patch where the nwfilter driver registers the functions to
instantiate and teardown the nwfilters with a function in
conf/domain_nwfilter.c called virDomainConfNWFilterRegister. Previous
helper functions that were called from qemu_driver.c and qemu_conf.c
were move into conf/domain_nwfilter.h with slight renaming done for
consistency. Those functions now call the function expored by
domain_nwfilter.c, which in turn call the functions of the new driver
interface, if available.

When a filter is updated, only those interfaces must have their old
rules cleared that either reference the filter directly or indirectly
through another filter. Remember between the different steps of the
instantiation of the filters which interfaces must be skipped. I am
using a hash map to remember the names of the interfaces and store a
bogus pointer to ~0 into it that need not be freed.

 - using INT_BUFSIZE_BOUND() to determine the length of the buffersize
for printing and integer into

 - not explicitly initializing static var threadsTerminate to false
anymore, since that's done automatically

Changes after V2:
  - removed while looks in case of OOM error
  - removed on ifaceDown() call
  - preceding one ifaceDown() call with an ifaceCheck() call

Since the name of an interface can be the same between stops and starts
of different VMs I have to switch the IP address learning thread to use
the index of the interface to determine whether an interface is still
available or not - in the case of macvtap the thread needs to listen for
traffic on the physical interface, thus having to time out periodically
to check whether the VM's macvtap device is still there as an indication
that the VM is still alive. Previously the following sequence of 2 VMs
with macvtap device

virsh start testvm1; virsh destroy testvm1 ; virsh start testvm2

would not terminate the thread upon testvm1's destroy since the name of
the interface on the host could be the same (i.e, macvtap0) on testvm1
and testvm2, thus it was easily race-able. The thread would then
determine the IP address parameter for testvm2 but apply the rule set
for testvm1. :-(
I am also introducing a lock for the interface (by name) that the thread
must hold while it listens for the traffic and releases when it
terminates upon VM termination or 0.5 second thereafter. Thus, the new
thread for a newly started VM with the same interface name will not
start while the old one still holds the lock. The only other code that I
see that also needs to grab the lock to serialize operation is the one
that tears down the firewall that were established on behalf of an
interface.

I am moving the code applying the 'basic' firewall rules during the IP
address learning phase inside the thread but won't start the thread
unless it is ensured that the firewall driver has the ability to apply
the 'basic' firewall rules.

To avoid race-conditions, the tear down of a filter has to happen before
the tap interface disappears and another tap interface with the same
name can re-appear. This patch tries to fix this. In one place, where
communication with the qemu monitor may fail, I am only tearing the
filters down after knowing that the function did not fail.

I am also moving the tear down functions into an include file for other
drivers to reuse.

I am getting rid of determining the path to necessary CLI tools at
compile time. Instead, now the firewall driver has an initialization
function that uses virFindFileInPath() to determine the path to
necessary CLI tools and a shutdown function to free allocated memory.
The rest of the patch mostly deals with availability of the CLI tools
and to not call certain code blocks if a tool is not available and that
strings now have to be built slightly differently.

Changes from v1 to v2:
- changed function name prefixes to 'iface' from previous 'Iface'

- Further to make make syntax-check pass:
 - indentation fix in interface.h
 - added entry to POTFILES.in

I am consolidating network interface related functions used in nwfilter
and macvtap code in utils/interface.c. All function names are prefixed
with 'Iface'. The following functions are now available through
interface.h:

int ifaceCtrl(const char *name, bool up);
int ifaceUp(const char *name);
int ifaceDown(const char *name);

int ifaceCheck(bool reportError, const char *ifname,
               const unsigned char *macaddr, int ifindex);

int ifaceGetIndex(bool reportError, const char *ifname, int *ifindex);

I added 'int ifindex' as parameter to ifaceCheck to the original
function and modified the code accordingly.

This patch implements support for learning a VM's IP address. It uses
the pcap library to listen on the VM's backend network interface (tap)
or the physical ethernet device (macvtap) and tries to capture packets
with source or destination MAC address of the VM and learn from DHCP
Offers, ARP traffic, or first-sent IPv4 packet what the IP address of
the VM's interface is. This then allows to instantiate the network
traffic filtering rules without the user having to provide the IP
parameter somewhere in the filter description or in the interface
description as a parameter. This only supports to detect the parameter
IP, which is for the assumed single IPv4 address of a VM. There is not
support for interfaces that may have multiple  IP addresses (IP
aliasing) or IPv6 that may then require more than one valid IP address
to be detected. A VM can have multiple independent interfaces that each
uses a different IP address and in that case it will be attempted to
detect each one of the address independently.

So, when for example an interface description in the domain XML has
looked like this up to now:

    <interface type='bridge'>
      <source bridge='mybridge'/>
      <model type='virtio'/>
      <filterref filter='clean-traffic'>
        <parameter name='IP' value='10.2.3.4'/>
      </filterref>
    </interface>

you may omit the IP parameter:

    <interface type='bridge'>
      <source bridge='mybridge'/>
      <model type='virtio'/>
      <filterref filter='clean-traffic'/>
    </interface>

Internally I am walking the 'tree' of a VM's referenced network filters
and determine with the given variables which variables are missing. Now,
the above IP parameter may be missing and this causes a libvirt-internal
thread to be started that uses the pcap library's API to listen to the
backend interface  (in case of macvtap to the physical interface) in an
attempt to determine the missing IP parameter. If the backend interface
disappears the thread terminates assuming the VM was brought down. In
case of a macvtap device a timeout is being used to wait for packets
from the given VM (filtering by VM's interface MAC address). If the VM's
macvtap device disappeared the thread also terminates. In all other
cases it tries to determine the IP address of the VM and will then apply
the rules late on the given interface, which would have happened
immediately if the IP parameter had been explicitly given. In case an
error happens while the firewall rules are applied, the VM's backend
interface is 'down'ed preventing it to communicate. Reasons for failure
for applying the network firewall rules may that an ebtables/iptables
command failes or OOM errors. Essentially the same failure reasons may
occur as when the firewall rules are applied immediately on VM start,
except that due to the late application of the filtering rules the VM
now is already running and cannot be hindered anymore from starting.
Bringing down the whole VM would probably be considered too drastic.
While a VM's IP address is attempted to be determined only limited
updates to network filters are allowed. In particular it is prevented
that filters are modified in such a way that they would introduce new
variables.

A caveat: The algorithm does not know which one is the appropriate IP
address of a VM. If the VM spoofs an IP address in its first ARP traffic
or IPv4 packets its filtering rules will be instantiated for this IP
address, thus 'locking' it to the found IP address. So, it's still
'safer' to explicitly provide the IP address of a VM's interface in the
filter description if it is known beforehand.

* configure.ac: detect libpcap
* libvirt.spec.in: require libpcap[-devel] if qemu is built
* src/internal.h: add the new ATTRIBUTE_PACKED define
* src/Makefile.am src/libvirt_private.syms: add the new modules and symbols
* src/nwfilter/nwfilter_learnipaddr.[ch]: new module being added
* src/nwfilter/nwfilter_driver.c src/conf/nwfilter_conf.[ch]
  src/nwfilter/nwfilter_ebiptables_driver.[ch]
  src/nwfilter/nwfilter_gentech_driver.[ch]: plu the new functionality in
* tests/nwfilterxml2xmltest: extend testing

This patch removes the virConnectPtr parameter from all functions where it's not necessary starting out with removing it as a parameter to the error reporting function.

This patch removes the driver dependency from nwfilter_conf.c and moves
a callback function calling into the driver into
nwfilter_gentech_driver.c and passes a pointer to that callback function
upon initialization of nwfilter_conf.c.

* src/conf/nwfilter_conf.h: Indent cpp directives.
* src/conf/nwfilter_params.h: Likewise.
* src/datatypes.h: Likewise.
* src/nwfilter/nwfilter_driver.h: Likewise.
* src/nwfilter/nwfilter_ebiptables_driver.h: Likewise.
* src/nwfilter/nwfilter_gentech_driver.h: Likewise.

This patch implements the core driver and provides
- management functionality for managing the filter XMLs
- compiling the internal filter representation into ebtables rules
- applying ebtables rules on a network (tap,macvtap) interface
- tearing down ebtables rules that were applied on behalf of an
interface
- updating of filters while VMs are running and causing the firewalls to
be rebuilt
- other bits and pieces
Signed-off-by: NStefan Berger <stefanb@us.ibm.com>