[libvirt] [PATCH 02/13] New virNetworkDef utility functions

[Laine Stump]

On 12/20/2010 06:52 PM, Eric Blake wrote:
> On 12/20/2010 01:03 AM, Laine Stump wrote:
>> Later patches will add the possibility to define a network's netmask
>> as a prefix (0-32, or 0-128 in the case of IPv6). To make it easier to
>> deal with definition of both kinds (prefix or netmask), add two new
>> functions:
>>
>> virNetworkDefNetmask: return a copy of the netmask into a
>> virSocketAddr. If no netmask was specified in the XML, create a
>> default netmask based on the network class of the virNetworkDef's IP
>> address.
>>
>> virNetworkDefPrefix: return the netmask as numeric prefix (or the
>> default prefix for the network class of the virNetworkDef's IP
>> address, if no netmask was specified in the XML)
> What happens if the user specifies a netmask in the XML that is
> non-contiguous (bad practice, but some routers do allow it)?

If that's the case,
>>
>> +/* return number of 1 bits in netmask for the network's ipAddress,
>> + * or -1 on error
>> + */
>> +int virNetworkDefPrefix(const virNetworkDefPtr def)
> Should this return different values, such as -1 if network class not
> determined, and -2 if netmask was specified but non-contiguous?  Or do
> callers not care?
>
>> +{
>> +    if (VIR_SOCKET_HAS_ADDR(&def->netmask)) {
>> +        return virSocketGetNumNetmaskBits(&def->netmask);
> [hmm, back to my theme of preferring direct operations over bitwise
> loops, I notice that the existing GetNumNetmaksBits implementation could
> be independently optimized]
>
>> +    } else if (VIR_SOCKET_IS_FAMILY(&def->ipAddress, AF_INET)) {
>> +        /* return the natural prefix for the network's ip address */
>> +        int addr = ntohl(def->ipAddress.data.inet4.sin_addr.s_addr);
>> +        if (IN_CLASSA(addr))
> Where is this defined?  Oh, I found it - in<netinet/in.h>, but only as
> a Linux extension.  Since POSIX doesn't require it to exist, you'll need
> to take care to provide fallback definitions for this macro and its friends.

If the raw numbers have to be in there anyway, I'd rather just do it by 
hand for all platforms.