manpage: Add a description of the 'softreval' / 'nosoftreval' mount option

Add a description of the 'softreval' / 'nosoftreval' mount options on
the 'nfs' generic manpage.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Steve Dickson <steved@redhat.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man
index 84462cd7..6f79c63a 100644
--- a/utils/mount/nfs.man
+++ b/utils/mount/nfs.man
@@ -121,6 +121,36 @@ option may mitigate some of the risks of using the
 .B soft
 option.
 .TP 1.5i
+.BR softreval " / " nosoftreval
+In cases where the NFS server is down, it may be useful to
+allow the NFS client to continue to serve up paths and
+attributes from cache after
+.B retrans
+attempts to revalidate that cache have timed out.
+This may, for instance, be helpful when trying to unmount a
+filesystem tree from a server that is permanently down.
+.IP
+It is possible to combine
+.BR softreval
+with the
+.B soft
+mount option, in which case operations that cannot be served up
+from cache will time out and return an error after
+.B retrans
+attempts. The combination with the default
+.B hard
+mount option implies those uncached operations will continue to
+retry until a response is received from the server.
+.IP
+Note: the default mount option is
+.BR nosoftreval
+which disallows fallback to cache when revalidation fails, and
+instead follows the behavior dictated by the
+.B hard
+or
+.B soft
+mount option.
+.TP 1.5i
 .BR intr " / " nointr
 This option is provided for backward compatibility.
 It is ignored after kernel 2.6.25.