[libvirt] [PATCH-v4 2/2] Support for static routes on a virtual bridge

[Gene Czarcinski]

On 04/25/2013 04:37 PM, Laine Stump wrote:
> On 04/25/2013 04:13 PM, Gene Czarcinski wrote:
>> On 04/25/2013 03:13 PM, Gene Czarcinski wrote:
>>> On 04/22/2013 11:59 AM, Laine Stump wrote:
>>>> address should be optional unless prefix or netmask is non-0, although
>>>> I've now noticed that won't be handled properly due to
>>>> virSocketAddrGetIpPrefix returning -1 when there is no address or
>>>> prefix
>>>> or netmask (I'm fixing that before I push that patch, so you can just
>>>> toss your 1/2 patch, rebase, and assume it's fixed).
>>> I have most of the stuff reworked except for the address, gateway,
>>> netmask, and prefix code.  Getting all of those balanced so they work
>>> correctly is a bit tricky..
>>>
>>> 1.  For <route>, I am requiring that both address= and gateway= be
>>> specified with address='0.0.0.0' and address='::' being valid
>>> addresses.  For IPv4, netmask='0.0.0.0' works correctly but prefix=0
>>> does not.
>>>
>>> For IPv4, address='0.0.0.0' results in a default route.  I am not
>>> sure what all these extra default routes are going to do to things
>>> but lets not get in the way of the experimenter.
>>>
>>> For IPv6, this address='::', prefix='0' is a slightly different
>>> matter as default routes are usually handled differently.  I am going
>>> to go ahead and implement it but I am not sure it is a good idea.
>>> "Normally," if you do not specify a prefix for IPv6, the default is
>>> 64.  But if you do specify one, then it will be used.
>>>
>>> It is getting real close and it should be ready "real soon now" ;))
>>>
>> AARRRRGH!!!!
>>
>> With IPv4 using address='0.0.0.0' and netmask='0.0.0.0' things work
>> just fine but with prefix not so much.  The problem is that with
>> prefix=0, it is not in the xml which then results it it defaulting at
>> a later time.  This is an extreme corner case.  Usually a zero prefix
>> is just ignored.
> Defaulting to what? I thought that when I pushed the utility function
> for that, I modified it to return a prefix of 0 if the address was
> 0.0.0.0 and neither netmask nor prefix was set.
>
> I guess it might be problematic if address was *not* 0 and you wanted an
> explicit 0 prefix, but I don't think that would ever be useful.
>
> If you really want prefix to show up in the xml if someone explicitly
> puts "prefix='0'" in there, you can add a "bool prefix_specified;" to
> the object, and set that when you see a prefix, even if it's 0. Then in
> the formatter you'll know that you should write out the value of prefix,
> even if it's 0.
>
> There are a few examples of doing this in either the network or domain
> xml parser/formatter - just search for occurrences of the word
> "_specified" in src/conf/*.[ch] and you'll find them.
>
>
OK, I have been trying all kinds of things in network_conf.c (which I 
now need to go back an clean up/simplify) because it is not the 
problem.  The real problem is in virSocketAddrGetIpPrefix().  For IPv4, 
a valid address is '0.0.0.0' and for IPv6 a similar address is '::' and 
both are valid addresses.  For IPv4, if a netmask of '0.0.0.0' is 
specified, things work but a prefix=0 is ignored/overridden.  For IPv6, 
the prefix=0 is also overriden with the default of 64.

To get this to work, I have to pass INVALID IPv4 and IPv6 addresses or 
not use the routine if the zero addresses are specified.  If the 
addresses are zero, then I believe we can correctly assume that a prefix 
of zero is also correct.  This code needs to be in bridge_driver.c.

Gene