[1/2] nfsd: fix NFSv4 time_delta attribute

Commit Message

Bruce Fields June 14, 2018, 7:21 p.m. UTC

From: "J. Bruce Fields" <[e-mail]>

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.

Signed-off-by: J. Bruce Fields <[e-mail]>
---
 fs/nfsd/nfs4xdr.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

Patch

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 59d471025949..4c5fa0ff2387 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2003,6 +2003,31 @@  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(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);
@@ -2794,9 +2819,7 @@  nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		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);