possible better error handling for nfsv4 and localhost maps

[Dave Sullivan <dsulliva@redhat.com>]

Hi All,

Recently we had a customer with some legacy maps using localhost run 
into a problem with NFSv4.

They are not quite ready to get rid of those localhost maps.

There is a fairly straight forward workaround/solution to get around 
this issue by modifying /etc/nfsmount.conf with

[ Server "localhost" ]
    Nfsvers=3

What we are asking for is better error handling so users can figure out 
what the problem is without having to debug as much.

i.e. Have the code not retry and have the code send a notification to 
syslog saying something like "nfsv4 does not support localhost maps, man 
nfsmount.conf, use [ Server "localhost" ] with Nfsvers=3 mount option to 
restrict localhost maps to NFSv3"

Here's an example of effort required to debug

Description of problem:

The RHEL automounter does try to do what’s inferred in the above 
notation, ie, make a bind mount.  What happens next, when the local 
filesystem doesn’t exist, is what’s causing us a problem.  It next 
spawns a mount request to an NFS service on localhost for the mount, 
either via IPV6, or via IPV4;  end-user hosts don’t serve NFS, so the 
problem arises due to how this is handled.

On RHEL5, the mount request contacts the portmapper, which reports there 
is no program registered for NFS service, and the mount fails straight away.

On RHEL6, if /etc/hosts has an entry for the IPV6 localhost address, an 
NFS mount from IPV6 localhost gets tried first, which fails immediately 
as expected, as IPV6 is not enabled, and no NFS service is registered on 
the host.  Automount reports the mount failure straight away.
Hi All,

Recently we had a customer with some legacy maps using localhost run 
into a problem with NFSv4.

They are not quite ready to get rid of those localhost maps.

There is a fairly straight forward workaround/solution to get around 
this issue by modifying /etc/nfsmount.conf with

[ Server "localhost" ]
    Nfsvers=3

What we are asking for is better error handling so users can figure out 
what the problem is without having to debug as much.

i.e. Have the code not retry and have the code send a notification to 
syslog saying something like "nfsv4 does not support localhost maps, man 
nfsmount.conf, use [ Server "localhost" ] with Nfsvers=3 mount option to 
restrict localhost maps to NFSv3"

Here's an example of effort required to debug

Description of problem:

The RHEL automounter does try to do what’s inferred in the above 
notation, ie, make a bind mount.  What happens next, when the local 
filesystem doesn’t exist, is what’s causing us a problem.  It next 
spawns a mount request to an NFS service on localhost for the mount, 
either via IPV6, or via IPV4;  end-user hosts don’t serve NFS, so the 
problem arises due to how this is handled.

On RHEL5, the mount request contacts the portmapper, which reports there 
is no program registered for NFS service, and the mount fails straight away.

On RHEL6, if /etc/hosts has an entry for the IPV6 localhost address, an 
NFS mount from IPV6 localhost gets tried first, which fails immediately 
as expected, as IPV6 is not enabled, and no NFS service is registered on 
the host.  Automount reports the mount failure straight away.

On RHEL6 however, if /etc/hosts does not have an entry for the IPV6 
localhost address, automount tries the IPV4 localhost address; when the 
mount is requested using NFSv4, the RPC request seem to get localhost 
port 0 returned for NFS service, instead of being told there is no 
program registered for NFS service (if I’m reading this strace correctly):

1657  1416223283.572722 socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 3
1657  1416223283.572764 bind(3, {sa_family=AF_INET, sin_port=htons(0), 
sin_addr=inet_addr("0.0.0.0")}, 16) = 0
1657  1416223283.572811 connect(3, {sa_family=AF_INET, 
sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
1657  1416223283.572849 getsockname(3, {sa_family=AF_INET, 
sin_port=htons(40477), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
1657  1416223283.572896 mount("localhost:/local/0/blah", "/mnt/test", 
"nfs", 0, "vers=4,addr=127.0.0.1,clientaddr"...) = -1 ECONNREFUSED 
(Connection refused)

The mount continues to pause and retry, until it reaches the retry 
limit, and then eventually fails.  Here’s what the bare mount command shows:

[root@lonlx8001b13 bevaja]# mount -vvv -t nfs -o nfsvers=4 
localhost:/local/0/blah /mnt/test
mount: fstab path: "/etc/fstab"
mount: mtab path:  "/etc/mtab"
mount: lock path:  "/etc/mtab~"
mount: temp path:  "/etc/mtab.tmp"
mount: UID:        0
mount: eUID:       0
mount: spec:  "localhost:/local/0/blah"
mount: node:  "/mnt/test"
mount: types: "nfs"
mount: opts:  "nfsvers=4"
final mount options: 'nfsvers=4'
mount: external mount: argv[0] = "/sbin/mount.nfs"
mount: external mount: argv[1] = "localhost:/local/0/blah"
mount: external mount: argv[2] = "/mnt/test"
mount: external mount: argv[3] = "-v"
mount: external mount: argv[4] = "-o"
mount: external mount: argv[5] = "rw,nfsvers=4"
mount.nfs: timeout set for Mon Nov 17 14:42:17 2014
mount.nfs: trying text-based options 
'nfsvers=4,addr=127.0.0.1,clientaddr=127.0.0.1'
mount.nfs: mount(2): Connection refused
mount.nfs: trying text-based options 
'nfsvers=4,addr=127.0.0.1,clientaddr=127.0.0.1'
mount.nfs: mount(2): Connection refused
mount.nfs: trying text-based options 
'nfsvers=4,addr=127.0.0.1,clientaddr=127.0.0.1'
mount.nfs: mount(2): Connection refused
mount.nfs: trying text-based options 
'nfsvers=4,addr=127.0.0.1,clientaddr=127.0.0.1'
mount.nfs: mount(2): Connection refused
mount.nfs: trying text-based options 
'nfsvers=4,addr=127.0.0.1,clientaddr=127.0.0.1'
mount.nfs: mount(2): Connection refused


Thoughts?

Thanks,

Dave
-- 

===================================================================
Dave Sullivan RHCE 			Email: dsulliva@redhat.com
Sr. Technical Account Manager 	

+1 312 660 3525 (Office)
+1 989 750 8385 (Cell)
===================================================================
Red Hat, Inc. | 100 East Davie St | Raleigh, NC | 27601

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