nfsd: fix handling of delegated change attr in CB_GETATTR

RFC8881, section 10.4.3 has some specific guidance as to how the
delegated change attribute should be handled. We currently don't follow
that guidance properly.

In particular, when the file is modified, the server always reports the
initial change attribute + 1. Section 10.4.3 however indicates that it
should be incremented on every GETATTR request from other clients.

Only request the change attribute until the file has been modified. If
there is an outstanding delegation, then increment the cached change
attribute on every GETATTR.

Fixes: 6487a13 ("NFSD: add support for CB_GETATTR callback")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: jtlayton

fs/nfsd/nfs4callback.c

@@ -361,12 +361,14 @@ static void
 encode_cb_getattr4args(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr,
 			struct nfs4_cb_fattr *fattr)
 {
-	struct nfs4_delegation *dp =
-		container_of(fattr, struct nfs4_delegation, dl_cb_fattr);
+	struct nfs4_delegation *dp = container_of(fattr, struct nfs4_delegation, dl_cb_fattr);
 	struct knfsd_fh *fh = &dp->dl_stid.sc_file->fi_fhandle;
+	struct nfs4_cb_fattr *ncf = &dp->dl_cb_fattr;
 	u32 bmap[1];
 
-	bmap[0] = FATTR4_WORD0_CHANGE | FATTR4_WORD0_SIZE;
+	bmap[0] = FATTR4_WORD0_SIZE;
+	if (!ncf->ncf_file_modified)
+		bmap[0] |= FATTR4_WORD0_CHANGE;
 
 	encode_nfs_cb_opnum4(xdr, OP_CB_GETATTR);
 	encode_nfs_fh4(xdr, fh);

fs/nfsd/nfs4xdr.c

@@ -2920,6 +2920,7 @@ struct nfsd4_fattr_args {
 	struct kstat		stat;
 	struct kstatfs		statfs;
 	struct nfs4_acl		*acl;
+	u64			change_attr;
 #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 	void			*context;
 	int			contextlen;
@@ -3019,7 +3020,6 @@ static __be32 nfsd4_encode_fattr4_change(struct xdr_stream *xdr,
 					 const struct nfsd4_fattr_args *args)
 {
 	const struct svc_export *exp = args->exp;
-	u64 c;
 
 	if (unlikely(exp->ex_flags & NFSEXP_V4ROOT)) {
 		u32 flush_time = convert_to_wallclock(exp->cd->flush_time);
@@ -3030,9 +3030,7 @@ static __be32 nfsd4_encode_fattr4_change(struct xdr_stream *xdr,
 			return nfserr_resource;
 		return nfs_ok;
 	}
-
-	c = nfsd4_change_attribute(&args->stat);
-	return nfsd4_encode_changeid4(xdr, c);
+	return nfsd4_encode_changeid4(xdr, args->change_attr);
 }
 
 static __be32 nfsd4_encode_fattr4_size(struct xdr_stream *xdr,
@@ -3557,11 +3555,16 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	if (dp) {
 		struct nfs4_cb_fattr *ncf = &dp->dl_cb_fattr;
 
-		if (ncf->ncf_file_modified)
+		if (ncf->ncf_file_modified) {
+			++ncf->ncf_initial_cinfo;
 			args.stat.size = ncf->ncf_cur_fsize;
-
+		}
+		args.change_attr = ncf->ncf_initial_cinfo;
 		nfs4_put_stid(&dp->dl_stid);
+	} else {
+		args.change_attr = nfsd4_change_attribute(&args.stat);
 	}
+
 	if (err)
 		goto out_nfserr;