nfsd: add fh_fsid_match helper

Add a helper to check that the fsid parts of two file handles match.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

fs/nfsd/nfsfh.h

@@ -196,6 +196,15 @@ static inline bool fh_match(struct knfsd_fh *fh1, struct knfsd_fh *fh2)
 	return true;
 }
 
+static inline bool fh_fsid_match(struct knfsd_fh *fh1, struct knfsd_fh *fh2)
+{
+	if (fh1->fh_fsid_type != fh2->fh_fsid_type)
+		return false;
+	if (memcmp(fh1->fh_fsid, fh2->fh_fsid, key_len(fh1->fh_fsid_type) != 0))
+		return false;
+	return true;
+}
+
 #ifdef CONFIG_NFSD_V3
 /*
  * The wcc data stored in current_fh should be cleared