Driver-Core: devtmpfs - remove EXPERIMENTAL and flush out the description

All major distros enable devtmpfs on recent systems, so remove
the EXPERIMENTAL flag, and make the description a bit more instructive.
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/Kconfig

@@ -9,29 +9,36 @@ config UEVENT_HELPER_PATH
 	  every uevent.
 
 config DEVTMPFS
-	bool "Create a kernel maintained /dev tmpfs (EXPERIMENTAL)"
+	bool "Maintain a devtmpfs filesystem to mount at /dev"
 	depends on HOTPLUG && SHMEM && TMPFS
 	help
-	  This creates a tmpfs filesystem, and mounts it at bootup
-	  and mounts it at /dev. The kernel driver core creates device
-	  nodes for all registered devices in that filesystem. All device
-	  nodes are owned by root and have the default mode of 0600.
-	  Userspace can add and delete the nodes as needed. This is
-	  intended to simplify bootup, and make it possible to delay
-	  the initial coldplug at bootup done by udev in userspace.
-	  It should also provide a simpler way for rescue systems
-	  to bring up a kernel with dynamic major/minor numbers.
-	  Meaningful symlinks, permissions and device ownership must
-	  still be handled by userspace.
-	  If unsure, say N here.
+	  This creates a tmpfs filesystem instance early at bootup.
+	  In this filesystem, the kernel driver core maintains device
+	  nodes with their default names and permissions for all
+	  registered devices with an assigned major/minor number.
+	  Userspace can modify the filesystem content as needed, add
+	  symlinks, and apply needed permissions.
+	  It provides a fully functional /dev directory, where usually
+	  udev runs on top, managing permissions and adding meaningful
+	  symlinks.
+	  In very limited environments, it may provide a sufficient
+	  functional /dev without any further help. It also allows simple
+	  rescue systems, and reliably handles dynamic major/minor numbers.
 
 config DEVTMPFS_MOUNT
-	bool "Automount devtmpfs at /dev"
+	bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
 	depends on DEVTMPFS
 	help
-	  This will mount devtmpfs at /dev if the kernel mounts the root
-	  filesystem. It will not affect initramfs based mounting.
-	  If unsure, say N here.
+	  This will instruct the kernel to automatically mount the
+	  devtmpfs filesystem at /dev, directly after the kernel has
+	  mounted the root filesystem. The behavior can be overridden
+	  with the commandline parameter: devtmpfs.mount=0|1.
+	  This option does not affect initramfs based booting, here
+	  the devtmpfs filesystem always needs to be mounted manually
+	  after the roots is mounted.
+	  With this option enabled, it allows to bring up a system in
+	  rescue mode with init=/bin/sh, even when the /dev directory
+	  on the rootfs is completely empty.
 
 config STANDALONE
 	bool "Select only drivers that don't need compile-time external firmware" if EXPERIMENTAL