Re: [PATCH] mount.nfs: prefer IPv4 addresses over IPv6 (try #2)

[Chuck Lever <chuck.lever@oracle.com>]

On 01/21/2010 02:15 PM, J. Bruce Fields wrote:
> On Wed, Jan 20, 2010 at 10:36:36AM -0500, Chuck Lever wrote:
>> For the record, we looked at Solaris behavior yesterday.  With bi-family
>> servers, its mount command tries IPv6 first, but appears smart enough to
>> fall back to IPv4.  One thing we haven't tried is to see how difficult it
>> would be to fix the real problem by adding proper protocol family
>> negotiation to our own mount command.
>
> Sorry, I probably just haven't been following: what's "proper protocol
> family negotiation"?  I thought the only ways to negotiate were either
> rpcbind (v2, v3) or trial and error (v4)?

In TI-RPC parlance, a "protocol" is the transport protocol (UDP, for 
example), and a "protocol family" is the address family ("inet6", for 
example).  A netid represents a particular combination of the two:  the 
netid "udp6" represents UDP over "inet6".

The "protocol family" is really the value that is passed to socket(2). 
This call generally takes PF_INET or something like that as its first 
argument.  All of the PF_FOO thingies have the same integer value as 
their AF_FOO counterparts.  For TI-RPC, we have "inet" and "inet6", 
which are strings that match up with the AF_FOO and PF_FOO names.

rpcb_getaddr(3t) is designed to use the rpcbind protocol to determine 
the address and transport to use when contacting a remote service.  Our
mount command has its own negotiation mechanism that is a superset of 
rpcbind calls, in addition to having a faster timeout than rpcb_getaddr(3t).

Until now, mount.nfs hasn't needed to negotiate the protocol family in 
addition to the NFS and mount versions and transports.  It always 
assumed "inet" (or AF_INET, or PF_INET), and until recently, used only 
rpcbind protocol version 2.

-- 
chuck[dot]lever[at]oracle[dot]com