On Sep 6, 2010, at 9:32 PM, Neil Brown wrote:
> On Tue, 31 Aug 2010 12:38:09 -0400
> Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
>
>>>>
>>>>> + /* OK to try different protocols. Lets see
>>>>> + * what portmap thinks.
>>>>> + */
>>>>> + int oldfake = mi->fake;
>>>>> + int res;
>>>>> + mi->fake = 1;
>>>>> + res = nfs_try_mount_v3v2(mi);
>>>>
>>>> If you just want to probe the server's portmapper, I think you can use nfs_probe_bothports() directly.
>>>>
>>>
>>> Not quite. You would need to wrap it in a loop over all addresses in
>>> md->address, and would need to worry about the mounthost option. It seems
>>> easier to just call nfs_try_mount_v3v2 which already does this.
>>
>> /me smacks forehead
>>
>> Complexity that I guess we have to live with. A comment that explains the oldfake hack would be helpful.
>
> And often trying to write such a comment can make it clear why the code was a
> bad idea in the first place.... :-)
>
> Rather than write a comment I wouldn't believe myself, here is something
> quite different - my third draft.
> This is on top of the nice tidy-up patches you posted earlier.
>
> It uses nfs_getport to make very focussed requests to portmap.
>
> Two things I'm still not really sure about:
>
> 1/ RDMA. How does that interact with fallback. Do we only support v4 over
> RDMA? That would be nice was we could simply avoid fallback in that case.
My impression is that today RDMA is stable only on vers=3; someday it should be stable with vers=4 too.
I think Steve and I need to agree on the final form of the RDMA patches before we can say with authority how fallback will work.
> 2/ IPv6. I should possibly be checking if v3v2 are available via UDP6 as well
> as UDP - and similarly if v4 has become available via TCP6?? Or is that
> all magically handled somewhere under the hood?
nfs_try_mount_v4() will try all address families provided by getaddrinfo(3). So when ECONNREFUSED finally bubbles up to nfs_try_mount(), mount.nfs should have already tried NFSv4 via both tcp and tcp6.
Anyway, this seems to answer my original question about "what are the risks of trying the portmapper-based approach?" It looks like a complex solution no matter what.
I'm not suggesting you abandon this direction, but if the nfs_try_mount() logic does nothing more but fallback to v2/v3 if the NFSv4 mount attempt fails with ECONNREFUSED, what harm could that cause?
> From 60dae9b9c14869ae630db683e2524ad230064b19 Mon Sep 17 00:00:00 2001
> From: Neil Brown <neilb@xxxxxxx>
> Date: Tue, 7 Sep 2010 11:23:02 +1000
> Subject: [PATCH] mount: correctly handle fallback for ECONNREFUSED during mount attempt.
>
> If we get ECONNREFUSED when attempting a v4 mount, it could be that
> the server just isn't ready yet (the current assumption) or it could
> be that the server only support UDP - and thus only v3/v2. The latter
> possibility isn't handled currently.
>
> So if we get ECONNREFUSED when fallback is an option, check with
> portmap/rpcbind to see if it could be that case that v2/v3 are
> supported over UDP, and v4 still is not. In that case, fall back to v2v3.
>
> I'm not at all sure if IPv6 possibilities are RDMA are handled correctly..
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
>
> diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
> index 9e29a19..5ebcf3e 100644
> --- a/utils/mount/stropts.c
> +++ b/utils/mount/stropts.c
> @@ -750,6 +750,7 @@ static int nfs_autonegotiate(struct nfsmount_info *mi)
> {
> unsigned long protocol;
> int result;
> + struct addrinfo *ai;
>
> /*
> * If UDP was requested from the command line, try
> @@ -796,6 +797,33 @@ static int nfs_autonegotiate(struct nfsmount_info *mi)
> /* Linux servers prior to 2.6.25 may return
> * EPERM when NFS version 4 is not supported. */
> goto fall_back;
> + case ECONNREFUSED:
> + /* Either the server doesn't accept TCP connections,
> + * or it just isn't quite ready yet.
> + * In the first case, fall back to v3v2, in the second
> + * return failure - as this isn't a permanent error
> + * the attempt will be retried.
> + * To determine which, we need to check with portmap/rpcbind.
> + * If v2 or v3 are supported on UDP, but v4 isn't on TCP then fall-back.
> + */
> + for (ai = mi->address; ai != NULL; ai = ai->ai_next) {
> + if (nfs_getport(ai->ai_addr, ai->ai_addrlen,
> + NFS_PROGRAM, 3, IPPROTO_UDP) != 0 ||
> + nfs_getport(ai->ai_addr, ai->ai_addrlen,
> + NFS_PROGRAM, 2, IPPROTO_UDP) != 0) {
> + if (nfs_getport(ai->ai_addr, ai->ai_addrlen,
> + NFS_PROGRAM, 4, IPPROTO_TCP) != 0) {
> + /* v4 support is almost online, wait for it. */
> + errno = ECONNREFUSED;
> + return result;
> + } else
> + /* v2/v3 is supported, but v4 isn't, fall_back */
> + goto fall_back;
> + }
> + }
> + /* portmap is not responding yet either, so just try again */
> + errno = ECONNREFUSED;
> + return result;
> default:
> return result;
> }
--
chuck[dot]lever[at]oracle[dot]com
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