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The current documentation here is out of date, and not quite right.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

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 7ab70ff212d80a58dd66ba1f711967996933955f..413cb8ef951baae9b3066afd2f65fbd791d19ccb 100644 (file)
--- 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;