staging: Add VirtualBox guest shared folder (vboxsf) support

VirtualBox hosts can share folders with guests, this commit adds a
VFS driver implementing the Linux-guest side of this, allowing folders
exported by the host to be mounted under Linux.

This driver depends on the guest <-> host IPC functions exported by
the vboxguest driver.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20191028111744.143863-2-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -17335,6 +17335,12 @@ F:	include/linux/vbox_utils.h
 F:	include/uapi/linux/vbox*.h
 F:	drivers/virt/vboxguest/
 
+VIRTUAL BOX SHARED FOLDER VFS DRIVER:
+M:	Hans de Goede <hdegoede@redhat.com>
+L:	linux-fsdevel@vger.kernel.org
+S:	Maintained
+F:	drivers/staging/vboxsf/*
+
 VIRTUAL SERIO DEVICE DRIVER
 M:	Stephen Chandler Paul <thatslyude@gmail.com>
 S:	Maintained

drivers/staging/Kconfig

@@ -125,4 +125,6 @@ source "drivers/staging/exfat/Kconfig"
 
 source "drivers/staging/qlge/Kconfig"
 
+source "drivers/staging/vboxsf/Kconfig"
+
 endif # STAGING

drivers/staging/Makefile

@@ -53,3 +53,4 @@ obj-$(CONFIG_UWB)		+= uwb/
 obj-$(CONFIG_USB_WUSB)		+= wusbcore/
 obj-$(CONFIG_EXFAT_FS)		+= exfat/
 obj-$(CONFIG_QLGE)		+= qlge/
+obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/

drivers/staging/vboxsf/Kconfig

@@ -0,0 +1,10 @@
+config VBOXSF_FS
+	tristate "VirtualBox guest shared folder (vboxsf) support"
+	depends on X86 && VBOXGUEST
+	select NLS
+	help
+	  VirtualBox hosts can share folders with guests, this driver
+	  implements the Linux-guest side of this allowing folders exported
+	  by the host to be mounted under Linux.
+
+	  If you want to use shared folders in VirtualBox guests, answer Y or M.

drivers/staging/vboxsf/Makefile

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: MIT
+
+obj-$(CONFIG_VBOXSF_FS) += vboxsf.o
+
+vboxsf-y := dir.o file.o utils.o vboxsf_wrappers.o super.o

drivers/staging/vboxsf/TODO

@@ -0,0 +1,7 @@
+TODO:
+- Find a file-system developer to review this and give their Reviewed-By
+- Address any items coming up during review
+- Move to fs/vboxfs
+
+Please send any patches to Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+and Hans de Goede <hdegoede@redhat.com>