nfsd: add a new config option for the block layout driver

Split the config symbols into a generic pNFS one, which is invisible
and gets selected by the layout drivers, and one for the block layout
driver.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/Kconfig b/fs/nfsd/Kconfig
index a0b77fc..eb70d91 100644
--- a/fs/nfsd/Kconfig
+++ b/fs/nfsd/Kconfig
@@ -84,12 +84,17 @@
 	  If unsure, say N.
 
 config NFSD_PNFS
-	bool "NFSv4.1 server support for Parallel NFS (pNFS)"
+	bool
+
+config NFSD_BLOCKLAYOUT
+	bool "NFSv4.1 server support for pNFS block layouts"
 	depends on NFSD_V4
+	select NFSD_PNFS
 	help
-	  This option enables support for the parallel NFS features of the
-	  minor version 1 of the NFSv4 protocol (RFC5661) in the kernel's NFS
-	  server.
+	  This option enables support for the exporting pNFS block layouts
+	  in the kernel's NFS server. The pNFS block layout enables NFS
+	  clients to directly perform I/O to block devices accesible to both
+	  the server and the clients.  See RFC 5663 for more details.
 
 	  If unsure, say N.