nfsd4: document lease/grace-period limits

The current documentation here is out of date, and not quite right.

(Future work: some user documentation would be useful.)

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 12 insertions, 3 deletions

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 7ab70ff212d8..413cb8ef951b 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1208,9 +1208,6 @@ static ssize_t write_maxblksize(struct file *file, char *buf, size_t size)
 #ifdef CONFIG_NFSD_V4
 static ssize_t __nfsd4_write_time(struct file *file, char *buf, size_t size, time_t *time)
 {
-        /* if size > 10 seconds, call
-         * nfs4_reset_lease() then write out the new lease (seconds) as reply
-         */
         char *mesg = buf;
         int rv, i;
 
@@ -1220,6 +1217,18 @@ static ssize_t __nfsd4_write_time(struct file *file, char *buf, size_t size, tim
                 rv = get_int(&mesg, &i);
                 if (rv)
                         return rv;
+                /*
+                 * Some sanity checking.  We don't have a reason for
+                 * these particular numbers, but problems with the
+                 * extremes are:
+                 *      - Too short: the briefest network outage may
+                 *        cause clients to lose all their locks.  Also,
+                 *        the frequent polling may be wasteful.
+                 *      - Too long: do you really want reboot recovery
+                 *        to take more than an hour?  Or to make other
+                 *        clients wait an hour before being able to
+                 *        revoke a dead client's locks?
+                 */
                 if (i < 10 || i > 3600)
                         return -EINVAL;
                 *time = i;