nfsd4: support change_attr_type attribute

The change attribute is what is used by clients to revalidate their
caches.  Our server may use i_version or ctime for that purpose.  Those
choices behave slightly differently, and it may be useful to the client
to know which we're using.  This attribute tells the client that.  The
Linux client doesn't yet use this attribute yet, though.

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

fs/nfsd/nfs4xdr.c

@@ -2891,6 +2891,16 @@ out_acl:
 			goto out;
 	}
 
+	if (bmval2 & FATTR4_WORD2_CHANGE_ATTR_TYPE) {
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
+			goto out_resource;
+		if (IS_I_VERSION(d_inode(dentry)))
+			*p++ = cpu_to_be32(NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR);
+		else
+			*p++ = cpu_to_be32(NFS4_CHANGE_TYPE_IS_TIME_METADATA);
+	}
+
 	if (bmval2 & FATTR4_WORD2_SECURITY_LABEL) {
 		status = nfsd4_encode_security_label(xdr, rqstp, context,
 								contextlen);

fs/nfsd/nfsd.h

@@ -360,6 +360,7 @@ void		nfsd_lockd_shutdown(void);
 
 #define NFSD4_2_SUPPORTED_ATTRS_WORD2 \
 	(NFSD4_1_SUPPORTED_ATTRS_WORD2 | \
+	FATTR4_WORD2_CHANGE_ATTR_TYPE | \
 	FATTR4_WORD2_MODE_UMASK | \
 	NFSD4_2_SECURITY_ATTRS)
 

include/linux/nfs4.h

@@ -374,6 +374,13 @@ enum lock_type4 {
 	NFS4_WRITEW_LT = 4
 };
 
+enum change_attr_type4 {
+	NFS4_CHANGE_TYPE_IS_MONOTONIC_INCR = 0,
+	NFS4_CHANGE_TYPE_IS_VERSION_COUNTER = 1,
+	NFS4_CHANGE_TYPE_IS_VERSION_COUNTER_NOPNFS = 2,
+	NFS4_CHANGE_TYPE_IS_TIME_METADATA = 3,
+	NFS4_CHANGE_TYPE_IS_UNDEFINED = 4
+};
 
 /* Mandatory Attributes */
 #define FATTR4_WORD0_SUPPORTED_ATTRS    (1UL << 0)
@@ -441,6 +448,7 @@ enum lock_type4 {
 #define FATTR4_WORD2_LAYOUT_BLKSIZE     (1UL << 1)
 #define FATTR4_WORD2_MDSTHRESHOLD       (1UL << 4)
 #define FATTR4_WORD2_CLONE_BLKSIZE	(1UL << 13)
+#define FATTR4_WORD2_CHANGE_ATTR_TYPE	(1UL << 15)
 #define FATTR4_WORD2_SECURITY_LABEL     (1UL << 16)
 #define FATTR4_WORD2_MODE_UMASK		(1UL << 17)