Re: [PATCH 3/6] nfs-utils: skip getaddrinfo in create_auth_rpc_client unless we need port

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

On Apr 3, 2009, at 3:04 PM, Jeff Layton wrote:
> On Wed, 1 Apr 2009 14:01:30 -0400
> Chuck Lever <chuck.lever@oracle.com> wrote:
>
>> As far as I understand it, the ai_socktype and ai_protocol fields are
>> used to return the values needed for subsequent socket(2)/bind(2)
>> system calls.  In this case you are not using these fields from the
>> results...
>>
>> If ai_protocol is zero, then getaddrinfo(3) assumes you want one copy
>> of the address for each supported protocol type, so it returns three
>> structures (one for IPPROTO_UDP, one for IPPROTO_TCP, and one with a
>> zero protocol number).  The contents, except for the socktype and
>> protocol fields, are the same for each.
>
> Hypothetical situation...
>
> Suppose there is a service in /etc/services that has a different port
> number for tcp than for udp:
>
> fooserv		50001/tcp
> fooserv		50002/udp
>
> You're saying that getaddrinfo will return the same port number in all
> of the returned structures? Won't that mean that one of the port  
> numbers
> is wrong? That seems broken if so...

I was trying to describe observed behavior here -- it's pretty  
unlikely that there will be different port numbers in these returned  
structures.  It's difficult to say precisely how this is supposed to  
behave based on the man page or even browsing the glibc source code  
for a few minutes.

It's certainly possible to set up /etc/services as you suggest, but  
there is an IANA policy to assign the same port for both transports.   
As near as I can tell the reason we have the transport listed in /etc/ 
services at all is because some protocols support only one transport.   
So IMO it would be quite unlikely to encounter such a case where the  
port number depended on the transport.

> If that's not the case, then I think we need to at least set the
> ai_protocol in the hints.

Perhaps that's true.  What are the expected values of @service ?

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