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

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
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='' and address='::' being valid
addresses.  For IPv4, netmask='' works correctly but prefix=0
does not.

For IPv4, address='' 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" ;))


With IPv4 using address='' and netmask='' 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 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 '' and for IPv6 a similar address is '::' and both are valid addresses. For IPv4, if a netmask of '' 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.


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