2 files changed, 11 insertions, 0 deletions

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index cb3dae2fcd86..c64d55f319bd 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1425,6 +1425,7 @@ static struct flags {
         { NFSEXP_CROSSMOUNT, {"crossmnt", ""}},
         { NFSEXP_NOSUBTREECHECK, {"no_subtree_check", ""}},
         { NFSEXP_NOAUTHNLM, {"insecure_locks", ""}},
+        { NFSEXP_V4ROOT, {"v4root", ""}},
 #ifdef MSNFS
         { NFSEXP_MSNFS, {"msnfs", ""}},
 #endif
diff --git a/include/linux/nfsd/export.h b/include/linux/nfsd/export.h
index 4cafbe1255f0..41f0d4e25374 100644
--- a/include/linux/nfsd/export.h
+++ b/include/linux/nfsd/export.h
@@ -39,6 +39,16 @@
 #define NFSEXP_FSID             0x2000
 #define NFSEXP_CROSSMOUNT       0x4000
 #define NFSEXP_NOACL            0x8000  /* reserved for possible ACL related use */
+/*
+ * The NFSEXP_V4ROOT flag causes the kernel to give access only to NFSv4
+ * clients, and only to the single directory that is the root of the
+ * export; further lookup and readdir operations are treated as if every
+ * subdirectory was a mountpoint, and ignored if they are not themselves
+ * exported.  This is used by nfsd and mountd to construct the NFSv4
+ * pseudofilesystem, which provides access only to paths leading to each
+ * exported filesystem.
+ */
+#define NFSEXP_V4ROOT           0x10000
 /* All flags that we claim to support.  (Note we don't support NOACL.) */
 #define NFSEXP_ALLFLAGS         0x7E3F