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



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)?

>  
> +/* 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.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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