mount.nfs: Update description of clientaddr= in nfs(5)

The description of clientaddr= in nfs(5) is out of date and omits some
other typical reasons for using it.  Expand its description.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Neil Brown <neilb@suse.de>

1 files changed, 17 insertions, 5 deletions

diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man
index e66daba..d92da19 100644
--- a/utils/mount/nfs.man
+++ b/utils/mount/nfs.man
@@ -411,11 +411,23 @@ Valid protocol types are
 and
 .IR tcp .
 .TP 1.5i
-.I clientaddr=n
-On a multi-homed client, this
-causes the client to use a specific callback address when
-communicating with an NFS version 4 server.
-This option is currently ignored.
+.I clientaddr=n.n.n.n
+Specifies a single IPv4 address in dotted-quad form that
+the NFS client advertises to allow servers to perform
+NFSv4 callback requests against files on this mount point.
+If the server is not able to establish callback connections
+to clients, performance may degrade, or accesses to
+files may temporarily hang.
+.IP
+If this option is not specified, the
+.BR mount (8)
+command attempts to discover an appropriate callback
+address automatically.
+The automatic discovery process is not perfect, however.
+In the presence of multiple client network interfaces, special
+routing policies, or atypical network topologies, the exact
+address to use for callbacks may be nontrivial to determine,
+and should be explicitly set using this mount option.
 .TP 1.5i
 .I sec=mode
 Same as \f3sec=mode\f1 for the nfs filesystem type (see above).