nfsd: skip some unnecessary stats in the v4 case

In the typical case of v4 and an i_version-supporting filesystem, we can
skip a stat which is only required to fake up a change attribute from
ctime.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs3xdr.c

@@ -364,6 +364,11 @@ encode_wcc_data(struct svc_rqst *rqstp, __be32 *p, struct svc_fh *fhp)
 	return encode_post_op_attr(rqstp, p, fhp);
 }
 
+static bool fs_supports_change_attribute(struct super_block *sb)
+{
+	return sb->s_flags & SB_I_VERSION || sb->s_export_op->fetch_iversion;
+}
+
 /*
  * Fill in the pre_op attr for the wcc data
  */
@@ -372,24 +377,26 @@ void fill_pre_wcc(struct svc_fh *fhp)
 	struct inode    *inode;
 	struct kstat	stat;
 	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
-	__be32 err;
 
 	if (fhp->fh_no_wcc || fhp->fh_pre_saved)
 		return;
 	inode = d_inode(fhp->fh_dentry);
-	err = fh_getattr(fhp, &stat);
+	if (fs_supports_change_attribute(inode->i_sb) || !v4) {
+		__be32 err = fh_getattr(fhp, &stat);
+
 		if (err) {
 			/* Grab the times from inode anyway */
 			stat.mtime = inode->i_mtime;
 			stat.ctime = inode->i_ctime;
 			stat.size  = inode->i_size;
 		}
-	if (v4)
-		fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);
-
 		fhp->fh_pre_mtime = stat.mtime;
 		fhp->fh_pre_ctime = stat.ctime;
 		fhp->fh_pre_size  = stat.size;
+	}
+	if (v4)
+		fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);
+
 	fhp->fh_pre_saved = true;
 }
 
@@ -400,7 +407,6 @@ void fill_post_wcc(struct svc_fh *fhp)
 {
 	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
 	struct inode *inode = d_inode(fhp->fh_dentry);
-	__be32 err;
 
 	if (fhp->fh_no_wcc)
 		return;
@@ -408,12 +414,16 @@ void fill_post_wcc(struct svc_fh *fhp)
 	if (fhp->fh_post_saved)
 		printk("nfsd: inode locked twice during operation.\n");
 
-	err = fh_getattr(fhp, &fhp->fh_post_attr);
+	fhp->fh_post_saved = true;
+
+	if (fs_supports_change_attribute(inode->i_sb) || !v4) {
+		__be32 err = fh_getattr(fhp, &fhp->fh_post_attr);
+
 		if (err) {
 			fhp->fh_post_saved = false;
 			fhp->fh_post_attr.ctime = inode->i_ctime;
-	} else
-		fhp->fh_post_saved = true;
+		}
+	}
 	if (v4)
 		fhp->fh_post_change =
 			nfsd4_change_attribute(&fhp->fh_post_attr, inode);