nfsd: fix NFSv4 time_delta attribute

Currently we return the worst-case value of 1 second in the time delta
attribute.  That's not terribly useful.  Instead, return a value
calculated from the time granularity supported by the filesystem and the
system clock.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index a96843c59fc146f1abb8c3a623984f29a083fefb..4161031ae14e3462a571ed61f2445b8a3452fa9b 100644 (file)
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2006,6 +2006,31 @@ static __be32 *encode_change(__be32 *p, struct kstat *stat, struct inode *inode,
        return p;
 }
 
+/*
+ * ctime (in NFSv4, time_metadata) is not writeable, and the client
+ * doesn't really care what resolution could theoretically be stored by
+ * the filesystem.
+ *
+ * The client cares how close together changes can be while still
+ * guaranteeing ctime changes.  For most filesystems (which have
+ * timestamps with nanosecond fields) that is limited by the resolution
+ * of the time returned from current_time() (which I'm assuming to be
+ * 1/HZ).
+ */
+static __be32 *encode_time_delta(__be32 *p, struct inode *inode)
+{
+       struct timespec ts;
+       u32 ns;
+
+       ns = max_t(u32, NSEC_PER_SEC/HZ, inode->i_sb->s_time_gran);
+       ts = ns_to_timespec(ns);
+
+       p = xdr_encode_hyper(p, ts.tv_sec);
+       *p++ = cpu_to_be32(ts.tv_nsec);
+
+       return p;
+}
+
 static __be32 *encode_cinfo(__be32 *p, struct nfsd4_change_info *c)
 {
        *p++ = cpu_to_be32(c->atomic);
@@ -2797,9 +2822,7 @@ out_acl:
                p = xdr_reserve_space(xdr, 12);
                if (!p)
                        goto out_resource;
-               *p++ = cpu_to_be32(0);
-               *p++ = cpu_to_be32(1);
-               *p++ = cpu_to_be32(0);
+               p = encode_time_delta(p, d_inode(dentry));
        }
        if (bmval1 & FATTR4_WORD1_TIME_METADATA) {
                p = xdr_reserve_space(xdr, 12);