usb: gadget: f_mass_storage: add configfs support

From this commit on f_mass_storage is available through configfs.
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/ABI/testing/configfs-usb-gadget-mass-storage

+What:		/config/usb-gadget/gadget/functions/mass_storage.name
+Date:		Oct 2013
+KenelVersion:	3.13
+Description:
+		The attributes:
+
+		stall		- Set to permit function to halt bulk endpoints.
+				Disabled on some USB devices known not to work
+				correctly. You should set it to true.
+		num_buffers	- Number of pipeline buffers. Valid numbers
+				are 2..4. Available only if
+				CONFIG_USB_GADGET_DEBUG_FILES is set.
+
+What:		/config/usb-gadget/gadget/functions/mass_storage.name/lun.name
+Date:		Oct 2013
+KenelVersion:	3.13
+Description:
+		The attributes:
+
+		file		- The path to the backing file for the LUN.
+				Required if LUN is not marked as removable.
+		ro		- Flag specifying access to the LUN shall be
+				read-only. This is implied if CD-ROM emulation
+				is enabled as well as when it was impossible
+				to open "filename" in R/W mode.
+		removable	- Flag specifying that LUN shall be indicated as
+				being removable.
+		cdrom		- Flag specifying that LUN shall be reported as
+				being a CD-ROM.
+		nofua		- Flag specifying that FUA flag
+				in SCSI WRITE(10,12)

drivers/usb/gadget/Kconfig

@@ -668,6 +668,17 @@ config USB_CONFIGFS_PHONET
 	help
 	  The Phonet protocol implementation for USB device.
 
+config USB_CONFIGFS_MASS_STORAGE
+	boolean "Mass storage"
+	depends on USB_CONFIGFS
+	select USB_U_MS
+	select USB_F_MASS_STORAGE
+	help
+	  The Mass Storage Gadget acts as a USB Mass Storage disk drive.
+	  As its storage repository it can use a regular file or a block
+	  device (in much the same way as the "loop" device driver),
+	  specified as a module parameter or sysfs option.
+
 config USB_ZERO
 	tristate "Gadget Zero (DEVELOPMENT)"
 	select USB_LIBCOMPOSITE

drivers/usb/gadget/f_mass_storage.h

@@ -71,10 +71,27 @@ struct fsg_operations {
 	int (*thread_exits)(struct fsg_common *common);
 };
 
+struct fsg_lun_opts {
+	struct config_group group;
+	struct fsg_lun *lun;
+	int lun_id;
+};
+
 struct fsg_opts {
 	struct fsg_common *common;
 	struct usb_function_instance func_inst;
+	struct fsg_lun_opts lun0;
+	struct config_group *default_groups[2];
 	bool no_configfs; /* for legacy gadgets */
+
+	/*
+	 * Read/write access to configfs attributes is handled by configfs.
+	 *
+	 * This is to protect the data from concurrent access by read/write
+	 * and create symlink/remove symlink.
+	 */
+	struct mutex			lock;
+	int				refcnt;
 };
 
 struct fsg_lun_config {