usb:composite: USB Mass Storage - storage_common.c from Linux kernel

The storage_common.c source file from v2.6.36 Linux kernel.

commit d26a6aa08b9f12b44fb1ee65625e7480d3d5bb81
Author: Michal Nazarewicz <m.nazarewicz@samsung.com>
Date:   Mon Nov 9 14:15:23 2009 +0100

USB: g_mass_storage: code cleaned up and comments updated

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
CC: Marek Vasut <marek.vasut@gmail.com>

1 files changed, 653 insertions, 0 deletions

diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
new file mode 100644
index 0000000..594dc10
--- /dev/null
+++ b/drivers/usb/gadget/storage_common.c
@@ -0,0 +1,653 @@
+/*
+ * storage_common.c -- Common definitions for mass storage functionality
+ *
+ * Copyright (C) 2003-2008 Alan Stern
+ * Copyeight (C) 2009 Samsung Electronics
+ * Author: Michal Nazarewicz (m.nazarewicz@samsung.com)
+ *
+ * Ported to u-boot:
+ * Andrzej Pietrasiewicz <andrzej.p@samsung.com>
+ *
+ * Code refactoring & cleanup:
+ * Łukasz Majewski <l.majewski@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+
+/*
+ * This file requires the following identifiers used in USB strings to
+ * be defined (each of type pointer to char):
+ *  - fsg_string_manufacturer -- name of the manufacturer
+ *  - fsg_string_product      -- name of the product
+ *  - fsg_string_serial       -- product's serial
+ *  - fsg_string_config       -- name of the configuration
+ *  - fsg_string_interface    -- name of the interface
+ * The first four are only needed when FSG_DESCRIPTORS_DEVICE_STRINGS
+ * macro is defined prior to including this file.
+ */
+
+/*
+ * When FSG_NO_INTR_EP is defined fsg_fs_intr_in_desc and
+ * fsg_hs_intr_in_desc objects as well as
+ * FSG_FS_FUNCTION_PRE_EP_ENTRIES and FSG_HS_FUNCTION_PRE_EP_ENTRIES
+ * macros are not defined.
+ *
+ * When FSG_NO_DEVICE_STRINGS is defined FSG_STRING_MANUFACTURER,
+ * FSG_STRING_PRODUCT, FSG_STRING_SERIAL and FSG_STRING_CONFIG are not
+ * defined (as well as corresponding entries in string tables are
+ * missing) and FSG_STRING_INTERFACE has value of zero.
+ *
+ * When FSG_NO_OTG is defined fsg_otg_desc won't be defined.
+ */
+
+/*
+ * When FSG_BUFFHD_STATIC_BUFFER is defined when this file is included
+ * the fsg_buffhd structure's buf field will be an array of FSG_BUFLEN
+ * characters rather then a pointer to void.
+ */
+
+
+/* #include <asm/unaligned.h> */
+
+
+/*
+ * Thanks to NetChip Technologies for donating this product ID.
+ *
+ * DO NOT REUSE THESE IDs with any other driver!!  Ever!!
+ * Instead:  allocate your own, using normal USB-IF procedures.
+ */
+#define FSG_VENDOR_ID	0x0525	/* NetChip */
+#define FSG_PRODUCT_ID	0xa4a5	/* Linux-USB File-backed Storage Gadget */
+
+/*-------------------------------------------------------------------------*/
+
+#ifndef DEBUG
+#undef VERBOSE_DEBUG
+#undef DUMP_MSGS
+#endif /* !DEBUG */
+
+#ifdef VERBOSE_DEBUG
+#define VLDBG	LDBG
+#else
+#define VLDBG(lun, fmt, args...) do { } while (0)
+#endif /* VERBOSE_DEBUG */
+
+/*
+#define LDBG(lun, fmt, args...)   dev_dbg (&(lun)->dev, fmt, ## args)
+#define LERROR(lun, fmt, args...) dev_err (&(lun)->dev, fmt, ## args)
+#define LWARN(lun, fmt, args...)  dev_warn(&(lun)->dev, fmt, ## args)
+#define LINFO(lun, fmt, args...)  dev_info(&(lun)->dev, fmt, ## args)
+*/
+
+#define LDBG(lun, fmt, args...) do { } while (0)
+#define LERROR(lun, fmt, args...) do { } while (0)
+#define LWARN(lun, fmt, args...) do { } while (0)
+#define LINFO(lun, fmt, args...) do { } while (0)
+
+/*
+ * Keep those macros in sync with those in
+ * include/linux/usb/composite.h or else GCC will complain.  If they
+ * are identical (the same names of arguments, white spaces in the
+ * same places) GCC will allow redefinition otherwise (even if some
+ * white space is removed or added) warning will be issued.
+ *
+ * Those macros are needed here because File Storage Gadget does not
+ * include the composite.h header.  For composite gadgets those macros
+ * are redundant since composite.h is included any way.
+ *
+ * One could check whether those macros are already defined (which
+ * would indicate composite.h had been included) or not (which would
+ * indicate we were in FSG) but this is not done because a warning is
+ * desired if definitions here differ from the ones in composite.h.
+ *
+ * We want the definitions to match and be the same in File Storage
+ * Gadget as well as Mass Storage Function (and so composite gadgets
+ * using MSF).  If someone changes them in composite.h it will produce
+ * a warning in this file when building MSF.
+ */
+
+#define DBG(d, fmt, args...)     debug(fmt , ## args)
+#define VDBG(d, fmt, args...)    debug(fmt , ## args)
+/* #define ERROR(d, fmt, args...)   printf(fmt , ## args) */
+/* #define WARNING(d, fmt, args...) printf(fmt , ## args) */
+/* #define INFO(d, fmt, args...)    printf(fmt , ## args) */
+
+/* #define DBG(d, fmt, args...)     do { } while (0) */
+/* #define VDBG(d, fmt, args...)    do { } while (0) */
+#define ERROR(d, fmt, args...)   do { } while (0)
+#define WARNING(d, fmt, args...) do { } while (0)
+#define INFO(d, fmt, args...)    do { } while (0)
+
+#ifdef DUMP_MSGS
+
+/* dump_msg(fsg, const char * label, const u8 * buf, unsigned length); */
+# define dump_msg(fsg, label, buf, length) do {                         \
+	if (length < 512) {						\
+		DBG(fsg, "%s, length %u:\n", label, length);		\
+		print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET,	\
+			       16, 1, buf, length, 0);			\
+	}								\
+} while (0)
+
+#  define dump_cdb(fsg) do { } while (0)
+
+#else
+
+#  define dump_msg(fsg, /* const char * */ label, \
+		   /* const u8 * */ buf, /* unsigned */ length) do { } while (0)
+
+#  ifdef VERBOSE_DEBUG
+
+#    define dump_cdb(fsg)						\
+	print_hex_dump(KERN_DEBUG, "SCSI CDB: ", DUMP_PREFIX_NONE,	\
+		       16, 1, (fsg)->cmnd, (fsg)->cmnd_size, 0)		\
+
+#  else
+
+#    define dump_cdb(fsg) do { } while (0)
+
+#  endif /* VERBOSE_DEBUG */
+
+#endif /* DUMP_MSGS */
+
+/*-------------------------------------------------------------------------*/
+
+/* SCSI device types */
+#define TYPE_DISK	0x00
+#define TYPE_CDROM	0x05
+
+/* USB protocol value = the transport method */
+#define USB_PR_CBI	0x00		/* Control/Bulk/Interrupt */
+#define USB_PR_CB	0x01		/* Control/Bulk w/o interrupt */
+#define USB_PR_BULK	0x50		/* Bulk-only */
+
+/* USB subclass value = the protocol encapsulation */
+#define USB_SC_RBC	0x01		/* Reduced Block Commands (flash) */
+#define USB_SC_8020	0x02		/* SFF-8020i, MMC-2, ATAPI (CD-ROM) */
+#define USB_SC_QIC	0x03		/* QIC-157 (tape) */
+#define USB_SC_UFI	0x04		/* UFI (floppy) */
+#define USB_SC_8070	0x05		/* SFF-8070i (removable) */
+#define USB_SC_SCSI	0x06		/* Transparent SCSI */
+
+/* Bulk-only data structures */
+
+/* Command Block Wrapper */
+struct fsg_bulk_cb_wrap {
+	__le32	Signature;		/* Contains 'USBC' */
+	u32	Tag;			/* Unique per command id */
+	__le32	DataTransferLength;	/* Size of the data */
+	u8	Flags;			/* Direction in bit 7 */
+	u8	Lun;			/* LUN (normally 0) */
+	u8	Length;			/* Of the CDB, <= MAX_COMMAND_SIZE */
+	u8	CDB[16];		/* Command Data Block */
+};
+
+#define USB_BULK_CB_WRAP_LEN	31
+#define USB_BULK_CB_SIG		0x43425355	/* Spells out USBC */
+#define USB_BULK_IN_FLAG	0x80
+
+/* Command Status Wrapper */
+struct bulk_cs_wrap {
+	__le32	Signature;		/* Should = 'USBS' */
+	u32	Tag;			/* Same as original command */
+	__le32	Residue;		/* Amount not transferred */
+	u8	Status;			/* See below */
+};
+
+#define USB_BULK_CS_WRAP_LEN	13
+#define USB_BULK_CS_SIG		0x53425355	/* Spells out 'USBS' */
+#define USB_STATUS_PASS		0
+#define USB_STATUS_FAIL		1
+#define USB_STATUS_PHASE_ERROR	2
+
+/* Bulk-only class specific requests */
+#define USB_BULK_RESET_REQUEST		0xff
+#define USB_BULK_GET_MAX_LUN_REQUEST	0xfe
+
+/* CBI Interrupt data structure */
+struct interrupt_data {
+	u8	bType;
+	u8	bValue;
+};
+
+#define CBI_INTERRUPT_DATA_LEN		2
+
+/* CBI Accept Device-Specific Command request */
+#define USB_CBI_ADSC_REQUEST		0x00
+
+/* Length of a SCSI Command Data Block */
+#define MAX_COMMAND_SIZE	16
+
+/* SCSI commands that we recognize */
+#define SC_FORMAT_UNIT			0x04
+#define SC_INQUIRY			0x12
+#define SC_MODE_SELECT_6		0x15
+#define SC_MODE_SELECT_10		0x55
+#define SC_MODE_SENSE_6			0x1a
+#define SC_MODE_SENSE_10		0x5a
+#define SC_PREVENT_ALLOW_MEDIUM_REMOVAL	0x1e
+#define SC_READ_6			0x08
+#define SC_READ_10			0x28
+#define SC_READ_12			0xa8
+#define SC_READ_CAPACITY		0x25
+#define SC_READ_FORMAT_CAPACITIES	0x23
+#define SC_READ_HEADER			0x44
+#define SC_READ_TOC			0x43
+#define SC_RELEASE			0x17
+#define SC_REQUEST_SENSE		0x03
+#define SC_RESERVE			0x16
+#define SC_SEND_DIAGNOSTIC		0x1d
+#define SC_START_STOP_UNIT		0x1b
+#define SC_SYNCHRONIZE_CACHE		0x35
+#define SC_TEST_UNIT_READY		0x00
+#define SC_VERIFY			0x2f
+#define SC_WRITE_6			0x0a
+#define SC_WRITE_10			0x2a
+#define SC_WRITE_12			0xaa
+
+/* SCSI Sense Key/Additional Sense Code/ASC Qualifier values */
+#define SS_NO_SENSE				0
+#define SS_COMMUNICATION_FAILURE		0x040800
+#define SS_INVALID_COMMAND			0x052000
+#define SS_INVALID_FIELD_IN_CDB			0x052400
+#define SS_LOGICAL_BLOCK_ADDRESS_OUT_OF_RANGE	0x052100
+#define SS_LOGICAL_UNIT_NOT_SUPPORTED		0x052500
+#define SS_MEDIUM_NOT_PRESENT			0x023a00
+#define SS_MEDIUM_REMOVAL_PREVENTED		0x055302
+#define SS_NOT_READY_TO_READY_TRANSITION	0x062800
+#define SS_RESET_OCCURRED			0x062900
+#define SS_SAVING_PARAMETERS_NOT_SUPPORTED	0x053900
+#define SS_UNRECOVERED_READ_ERROR		0x031100
+#define SS_WRITE_ERROR				0x030c02
+#define SS_WRITE_PROTECTED			0x072700
+
+#define SK(x)		((u8) ((x) >> 16))	/* Sense Key byte, etc. */
+#define ASC(x)		((u8) ((x) >> 8))
+#define ASCQ(x)		((u8) (x))
+
+struct device_attribute { int i; };
+struct rw_semaphore { int i; };
+#define down_write(...)			do { } while (0)
+#define up_write(...)			do { } while (0)
+#define down_read(...)			do { } while (0)
+#define up_read(...)			do { } while (0)
+#define ETOOSMALL	525
+
+#include <usb_mass_storage.h>
+extern struct ums_board_info		*ums_info;
+
+/*-------------------------------------------------------------------------*/
+
+struct fsg_lun {
+	loff_t		file_length;
+	loff_t		num_sectors;
+
+	unsigned int	initially_ro:1;
+	unsigned int	ro:1;
+	unsigned int	removable:1;
+	unsigned int	cdrom:1;
+	unsigned int	prevent_medium_removal:1;
+	unsigned int	registered:1;
+	unsigned int	info_valid:1;
+	unsigned int	nofua:1;
+
+	u32		sense_data;
+	u32		sense_data_info;
+	u32		unit_attention_data;
+
+	struct device	dev;
+};
+
+#define fsg_lun_is_open(curlun)	((curlun)->filp != NULL)
+#if 0
+static struct fsg_lun *fsg_lun_from_dev(struct device *dev)
+{
+	return container_of(dev, struct fsg_lun, dev);
+}
+#endif
+
+/* Big enough to hold our biggest descriptor */
+#define EP0_BUFSIZE	256
+#define DELAYED_STATUS	(EP0_BUFSIZE + 999)	/* An impossibly large value */
+
+/* Number of buffers we will use.  2 is enough for double-buffering */
+#define FSG_NUM_BUFFERS	2
+
+/* Default size of buffer length. */
+#define FSG_BUFLEN	((u32)16384)
+
+/* Maximal number of LUNs supported in mass storage function */
+#define FSG_MAX_LUNS	8
+
+enum fsg_buffer_state {
+	BUF_STATE_EMPTY = 0,
+	BUF_STATE_FULL,
+	BUF_STATE_BUSY
+};
+
+struct fsg_buffhd {
+#ifdef FSG_BUFFHD_STATIC_BUFFER
+	char				buf[FSG_BUFLEN];
+#else
+	void				*buf;
+#endif
+	enum fsg_buffer_state		state;
+	struct fsg_buffhd		*next;
+
+	/*
+	 * The NetChip 2280 is faster, and handles some protocol faults
+	 * better, if we don't submit any short bulk-out read requests.
+	 * So we will record the intended request length here.
+	 */
+	unsigned int			bulk_out_intended_length;
+
+	struct usb_request		*inreq;
+	int				inreq_busy;
+	struct usb_request		*outreq;
+	int				outreq_busy;
+};
+
+enum fsg_state {
+	/* This one isn't used anywhere */
+	FSG_STATE_COMMAND_PHASE = -10,
+	FSG_STATE_DATA_PHASE,
+	FSG_STATE_STATUS_PHASE,
+
+	FSG_STATE_IDLE = 0,
+	FSG_STATE_ABORT_BULK_OUT,
+	FSG_STATE_RESET,
+	FSG_STATE_INTERFACE_CHANGE,
+	FSG_STATE_CONFIG_CHANGE,
+	FSG_STATE_DISCONNECT,
+	FSG_STATE_EXIT,
+	FSG_STATE_TERMINATED
+};
+
+enum data_direction {
+	DATA_DIR_UNKNOWN = 0,
+	DATA_DIR_FROM_HOST,
+	DATA_DIR_TO_HOST,
+	DATA_DIR_NONE
+};
+
+/*-------------------------------------------------------------------------*/
+
+static inline u32 get_unaligned_be24(u8 *buf)
+{
+	return 0xffffff & (u32) get_unaligned_be32(buf - 1);
+}
+
+/*-------------------------------------------------------------------------*/
+
+enum {
+#ifndef FSG_NO_DEVICE_STRINGS
+	FSG_STRING_MANUFACTURER	= 1,
+	FSG_STRING_PRODUCT,
+	FSG_STRING_SERIAL,
+	FSG_STRING_CONFIG,
+#endif
+	FSG_STRING_INTERFACE
+};
+
+#ifndef FSG_NO_OTG
+static struct usb_otg_descriptor
+fsg_otg_desc = {
+	.bLength =		sizeof fsg_otg_desc,
+	.bDescriptorType =	USB_DT_OTG,
+
+	.bmAttributes =		USB_OTG_SRP,
+};
+#endif
+
+/* There is only one interface. */
+
+static struct usb_interface_descriptor
+fsg_intf_desc = {
+	.bLength =		sizeof fsg_intf_desc,
+	.bDescriptorType =	USB_DT_INTERFACE,
+
+	.bNumEndpoints =	2,		/* Adjusted during fsg_bind() */
+	.bInterfaceClass =	USB_CLASS_MASS_STORAGE,
+	.bInterfaceSubClass =	USB_SC_SCSI,	/* Adjusted during fsg_bind() */
+	.bInterfaceProtocol =	USB_PR_BULK,	/* Adjusted during fsg_bind() */
+	.iInterface =		FSG_STRING_INTERFACE,
+};
+
+/*
+ * Three full-speed endpoint descriptors: bulk-in, bulk-out, and
+ * interrupt-in.
+ */
+
+static struct usb_endpoint_descriptor
+fsg_fs_bulk_in_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	.bEndpointAddress =	USB_DIR_IN,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	/* wMaxPacketSize set by autoconfiguration */
+};
+
+static struct usb_endpoint_descriptor
+fsg_fs_bulk_out_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	.bEndpointAddress =	USB_DIR_OUT,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	/* wMaxPacketSize set by autoconfiguration */
+};
+
+#ifndef FSG_NO_INTR_EP
+
+static struct usb_endpoint_descriptor
+fsg_fs_intr_in_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	.bEndpointAddress =	USB_DIR_IN,
+	.bmAttributes =		USB_ENDPOINT_XFER_INT,
+	.wMaxPacketSize =	cpu_to_le16(2),
+	.bInterval =		32,	/* frames -> 32 ms */
+};
+
+#ifndef FSG_NO_OTG
+#  define FSG_FS_FUNCTION_PRE_EP_ENTRIES	2
+#else
+#  define FSG_FS_FUNCTION_PRE_EP_ENTRIES	1
+#endif
+
+#endif
+
+static struct usb_descriptor_header *fsg_fs_function[] = {
+#ifndef FSG_NO_OTG
+	(struct usb_descriptor_header *) &fsg_otg_desc,
+#endif
+	(struct usb_descriptor_header *) &fsg_intf_desc,
+	(struct usb_descriptor_header *) &fsg_fs_bulk_in_desc,
+	(struct usb_descriptor_header *) &fsg_fs_bulk_out_desc,
+#ifndef FSG_NO_INTR_EP
+	(struct usb_descriptor_header *) &fsg_fs_intr_in_desc,
+#endif
+	NULL,
+};
+
+/*
+ * USB 2.0 devices need to expose both high speed and full speed
+ * descriptors, unless they only run at full speed.
+ *
+ * That means alternate endpoint descriptors (bigger packets)
+ * and a "device qualifier" ... plus more construction options
+ * for the configuration descriptor.
+ */
+static struct usb_endpoint_descriptor
+fsg_hs_bulk_in_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	/* bEndpointAddress copied from fs_bulk_in_desc during fsg_bind() */
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	.wMaxPacketSize =	cpu_to_le16(512),
+};
+
+static struct usb_endpoint_descriptor
+fsg_hs_bulk_out_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	/* bEndpointAddress copied from fs_bulk_out_desc during fsg_bind() */
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	.wMaxPacketSize =	cpu_to_le16(512),
+	.bInterval =		1,	/* NAK every 1 uframe */
+};
+
+#ifndef FSG_NO_INTR_EP
+
+static struct usb_endpoint_descriptor
+fsg_hs_intr_in_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+
+	/* bEndpointAddress copied from fs_intr_in_desc during fsg_bind() */
+	.bmAttributes =		USB_ENDPOINT_XFER_INT,
+	.wMaxPacketSize =	cpu_to_le16(2),
+	.bInterval =		9,	/* 2**(9-1) = 256 uframes -> 32 ms */
+};
+
+#ifndef FSG_NO_OTG
+#  define FSG_HS_FUNCTION_PRE_EP_ENTRIES	2
+#else
+#  define FSG_HS_FUNCTION_PRE_EP_ENTRIES	1
+#endif
+
+#endif
+
+static struct usb_descriptor_header *fsg_hs_function[] = {
+#ifndef FSG_NO_OTG
+	(struct usb_descriptor_header *) &fsg_otg_desc,
+#endif
+	(struct usb_descriptor_header *) &fsg_intf_desc,
+	(struct usb_descriptor_header *) &fsg_hs_bulk_in_desc,
+	(struct usb_descriptor_header *) &fsg_hs_bulk_out_desc,
+#ifndef FSG_NO_INTR_EP
+	(struct usb_descriptor_header *) &fsg_hs_intr_in_desc,
+#endif
+	NULL,
+};
+
+/* Maxpacket and other transfer characteristics vary by speed. */
+static struct usb_endpoint_descriptor *
+fsg_ep_desc(struct usb_gadget *g, struct usb_endpoint_descriptor *fs,
+		struct usb_endpoint_descriptor *hs)
+{
+	if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
+		return hs;
+	return fs;
+}
+
+/* Static strings, in UTF-8 (for simplicity we use only ASCII characters) */
+static struct usb_string		fsg_strings[] = {
+#ifndef FSG_NO_DEVICE_STRINGS
+	{FSG_STRING_MANUFACTURER,	fsg_string_manufacturer},
+	{FSG_STRING_PRODUCT,		fsg_string_product},
+	{FSG_STRING_SERIAL,		fsg_string_serial},
+	{FSG_STRING_CONFIG,		fsg_string_config},
+#endif
+	{FSG_STRING_INTERFACE,		fsg_string_interface},
+	{}
+};
+
+static struct usb_gadget_strings	fsg_stringtab = {
+	.language	= 0x0409,		/* en-us */
+	.strings	= fsg_strings,
+};
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * If the next two routines are called while the gadget is registered,
+ * the caller must own fsg->filesem for writing.
+ */
+
+static int fsg_lun_open(struct fsg_lun *curlun, const char *filename)
+{
+	int				ro;
+	int				rc = -EINVAL;
+	loff_t				size;
+	loff_t				num_sectors;
+	loff_t				min_sectors;
+
+	/* R/W if we can, R/O if we must */
+	ro = curlun->initially_ro;
+
+	ums_info->get_capacity(&(ums_info->ums_dev), &size);
+	if (size < 0) {
+		printf("unable to find file size: %s\n", filename);
+		rc = (int) size;
+		goto out;
+	}
+	num_sectors = size >> 9;	/* File size in 512-byte blocks */
+	min_sectors = 1;
+	if (num_sectors < min_sectors) {
+		printf("file too small: %s\n", filename);
+		rc = -ETOOSMALL;
+		goto out;
+	}
+
+	curlun->ro = ro;
+	curlun->file_length = size;
+	curlun->num_sectors = num_sectors;
+	debug("open backing file: %s\n", filename);
+	rc = 0;
+
+out:
+	return rc;
+}
+
+static void fsg_lun_close(struct fsg_lun *curlun)
+{
+}
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * Sync the file data, don't bother with the metadata.
+ * This code was copied from fs/buffer.c:sys_fdatasync().
+ */
+static int fsg_lun_fsync_sub(struct fsg_lun *curlun)
+{
+	return 0;
+}
+
+static void store_cdrom_address(u8 *dest, int msf, u32 addr)
+{
+	if (msf) {
+		/* Convert to Minutes-Seconds-Frames */
+		addr >>= 2;		/* Convert to 2048-byte frames */
+		addr += 2*75;		/* Lead-in occupies 2 seconds */
+		dest[3] = addr % 75;	/* Frames */
+		addr /= 75;
+		dest[2] = addr % 60;	/* Seconds */
+		addr /= 60;
+		dest[1] = addr;		/* Minutes */
+		dest[0] = 0;		/* Reserved */
+	} else {
+		/* Absolute sector */
+		put_unaligned_be32(addr, dest);
+	}
+}
+
+/*-------------------------------------------------------------------------*/