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



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.


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