v4.19.13 snapshot.
diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
new file mode 100644
index 0000000..b7559c6
--- /dev/null
+++ b/fs/nfsd/cache.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Request reply cache. This was heavily inspired by the
+ * implementation in 4.3BSD/4.4BSD.
+ *
+ * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#ifndef NFSCACHE_H
+#define NFSCACHE_H
+
+#include <linux/sunrpc/svc.h>
+
+/*
+ * Representation of a reply cache entry.
+ *
+ * Note that we use a sockaddr_in6 to hold the address instead of the more
+ * typical sockaddr_storage. This is for space reasons, since sockaddr_storage
+ * is much larger than a sockaddr_in6.
+ */
+struct svc_cacherep {
+ struct list_head c_lru;
+
+ unsigned char c_state, /* unused, inprog, done */
+ c_type, /* status, buffer */
+ c_secure : 1; /* req came from port < 1024 */
+ struct sockaddr_in6 c_addr;
+ __be32 c_xid;
+ u32 c_prot;
+ u32 c_proc;
+ u32 c_vers;
+ unsigned int c_len;
+ __wsum c_csum;
+ unsigned long c_timestamp;
+ union {
+ struct kvec u_vec;
+ __be32 u_status;
+ } c_u;
+};
+
+#define c_replvec c_u.u_vec
+#define c_replstat c_u.u_status
+
+/* cache entry states */
+enum {
+ RC_UNUSED,
+ RC_INPROG,
+ RC_DONE
+};
+
+/* return values */
+enum {
+ RC_DROPIT,
+ RC_REPLY,
+ RC_DOIT
+};
+
+/*
+ * Cache types.
+ * We may want to add more types one day, e.g. for diropres and
+ * attrstat replies. Using cache entries with fixed length instead
+ * of buffer pointers may be more efficient.
+ */
+enum {
+ RC_NOCACHE,
+ RC_REPLSTAT,
+ RC_REPLBUFF,
+};
+
+/* Cache entries expire after this time period */
+#define RC_EXPIRE (120 * HZ)
+
+/* Checksum this amount of the request */
+#define RC_CSUMLEN (256U)
+
+int nfsd_reply_cache_init(void);
+void nfsd_reply_cache_shutdown(void);
+int nfsd_cache_lookup(struct svc_rqst *);
+void nfsd_cache_update(struct svc_rqst *, int, __be32 *);
+int nfsd_reply_cache_stats_open(struct inode *, struct file *);
+
+#endif /* NFSCACHE_H */