From: Jeff Layton <jtlayton@poochiereds.net>
Subject: making the 'addr=' mount option an address hint
Date: Sun, 17 Jul 2005 11:38:28 -0400
Message-ID: <1121614708.6713.41.camel@localhost.localdomain>
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To: nfs@lists.sourceforge.net
Sender: nfs-admin@lists.sourceforge.net
Errors-To: nfs-admin@lists.sourceforge.net

Hi,
  I've been working on a fairly major overhaul of the autofs mount_nfs
code. One of the things I've recently added is making it prefer to mount
from server addresses that are on the same subnet as the client.

  Unfortunately, I've found that when the mount program does a
gethostbyname() call to get the address of the host, it simply picks the
first address in the list, without regard for how "close" it is to the
client.

The upshot of this is that if even autofs picks a replicated mount entry
that is on the same subnet as the client, we may end up mounting across
a router anyway.

A simple way to correct this would be to make autofs pass the address
instead of the hostname when calling "mount". However, that will make
for an ugly /proc/mounts, especially if we have a lot of automounted NFS
mounts (it's more human-friendly to keep the hostname info when looking
at the list of mounts).

So, what I'd like to do is roll a patch for mount to change the behavior
of the 'addr=' option. Instead of ignoring it, we'd treat it as an
address hint. If one of the addresses returned by gethostbyname()
matches this address, then we'd mount using that address. Otherwise, the
existing behavior would prevail (use the first address in the list).

I'm writing this to solicit some feedback before I dive in and start
working on it. Does this sound like a reasonable idea? Is there
something I'm not considering that would prevent this from working?

Thanks,
Jeff


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