USB: gadget: storage: optional SCSI WRITE FUA bit

MS Windows mounts removable storage in "Removal optimized mode" by
default. All the writes to the media are synchronous which is achieved
by setting FUA (Force Unit Access) bit in SCSI WRITE(10,12) commands.
This prevents I/O requests aggregation in block layer dramatically
decreasing performance.

This patch brings an option to accept or ignore mentioned bit
a) via specifying module parameter "nofua", or
b) through sysfs entry
/sys/devices/platform/_UDC_/gadget/gadget-lunX/nofua
(_UDC_ is the name of the USB Device Controller driver)

Patch is based on the work that was done by Denis Karpov for Maemo 5
platform.

Signed-off-by: Andy Shevchenko <[e-mail]>
Acked-by: Alan Stern <[e-mail]>
Cc: Denis Karpov <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: David Brownell <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-devices-platform-_UDC_-gadget

···
 		0 -> resumed
 
 		(_UDC_ is the name of the USB Device Controller driver)
+
+What:           /sys/devices/platform/_UDC_/gadget/gadget-lunX/nofua
+Date:           July 2010
+Contact:        Andy Shevchenko <[e-mail]>
+Description:
+		Show or set the reaction on the FUA (Force Unit Access) bit in
+		the SCSI WRITE(10,12) commands when a gadget in USB Mass
+		Storage mode.
+
+		Possible values are:
+			1 -> ignore the FUA flag
+			0 -> obey the FUA flag

drivers/usb/gadget/file_storage.c

···
  *	removable		Default false, boolean for removable media
  *	luns=N			Default N = number of filenames, number of
  *					LUNs to support
+ *	nofua=b[,b...]		Default false, booleans for ignore FUA flag
+ *					in SCSI WRITE(10,12) commands
  *	stall			Default determined according to the type of
  *					USB device controller (usually true),
  *					boolean to permit the driver to halt
···
  *					PAGE_CACHE_SIZE)
  *
  * If CONFIG_USB_FILE_STORAGE_TEST is not set, only the "file", "ro",
- * "removable", "luns", "stall", and "cdrom" options are available; default
- * values are used for everything else.
+ * "removable", "luns", "nofua", "stall", and "cdrom" options are available;
+ * default values are used for everything else.
  *
  * The pathnames of the backing files and the ro settings are available in
- * the attribute files "file" and "ro" in the lun<n> subdirectory of the
- * gadget's sysfs directory.  If the "removable" option is set, writing to
+ * the attribute files "file", "nofua", and "ro" in the lun<n> subdirectory of
+ * the gadget's sysfs directory.  If the "removable" option is set, writing to
  * these files will simulate ejecting/loading the medium (writing an empty
  * line means eject) and adjusting a write-enable tab.  Changes to the ro
  * setting are not allowed when the medium is loaded or if CD-ROM emulation
···
 static struct {
 	char		*file[FSG_MAX_LUNS];
 	int		ro[FSG_MAX_LUNS];
+	int		nofua[FSG_MAX_LUNS];
 	unsigned int	num_filenames;
 	unsigned int	num_ros;
+	unsigned int	num_nofuas;
 	unsigned int	nluns;
 
 	int		removable;
···
 
 module_param_array_named(ro, mod_data.ro, bool, &mod_data.num_ros, S_IRUGO);
 MODULE_PARM_DESC(ro, "true to force read-only");
+
+module_param_array_named(nofua, mod_data.nofua, bool, &mod_data.num_nofuas,
+		S_IRUGO);
+MODULE_PARM_DESC(nofua, "true to ignore SCSI WRITE(10,12) FUA bit");
 
 module_param_named(luns, mod_data.nluns, uint, S_IRUGO);
 MODULE_PARM_DESC(luns, "number of LUNs");
···
 			curlun->sense_data = SS_INVALID_FIELD_IN_CDB;
 			return -EINVAL;
 		}
-		if (fsg->cmnd[1] & 0x08) {	// FUA
+		/* FUA */
+		if (!curlun->nofua && (fsg->cmnd[1] & 0x08)) {
 			spin_lock(&curlun->filp->f_lock);
 			curlun->filp->f_flags |= O_DSYNC;
 			spin_unlock(&curlun->filp->f_lock);
···
 
 /* The write permissions and store_xxx pointers are set in fsg_bind() */
 static DEVICE_ATTR(ro, 0444, fsg_show_ro, NULL);
+static DEVICE_ATTR(nofua, 0644, fsg_show_nofua, NULL);
 static DEVICE_ATTR(file, 0444, fsg_show_file, NULL);
 
 
···
 		}
 	}
 
+	/* Only for removable media? */
+	dev_attr_nofua.attr.mode = 0644;
+	dev_attr_nofua.store = fsg_store_nofua;
+
 	/* Find out how many LUNs there should be */
 	i = mod_data.nluns;
 	if (i == 0)
···
 		curlun->ro = mod_data.cdrom || mod_data.ro[i];
 		curlun->initially_ro = curlun->ro;
 		curlun->removable = mod_data.removable;
+		curlun->nofua = mod_data.nofua[i];
 		curlun->dev.release = lun_release;
 		curlun->dev.parent = &gadget->dev;
 		curlun->dev.driver = &fsg_driver.driver;
···
 		}
 		if ((rc = device_create_file(&curlun->dev,
 					&dev_attr_ro)) != 0 ||
+				(rc = device_create_file(&curlun->dev,
+					&dev_attr_nofua)) != 0 ||
 				(rc = device_create_file(&curlun->dev,
 					&dev_attr_file)) != 0) {
 			device_unregister(&curlun->dev);
···
 				if (IS_ERR(p))
 					p = NULL;
 			}
-			LINFO(curlun, "ro=%d, file: %s\n",
-					curlun->ro, (p ? p : "(error)"));
+			LINFO(curlun, "ro=%d, nofua=%d, file: %s\n",
+			      curlun->ro, curlun->nofua, (p ? p : "(error)"));
 		}
 	}
 	kfree(pathbuf);

drivers/usb/gadget/storage_common.c

···
 	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;
···
 				  : curlun->initially_ro);
 }
 
+static ssize_t fsg_show_nofua(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct fsg_lun	*curlun = fsg_lun_from_dev(dev);
+
+	return sprintf(buf, "%u\n", curlun->nofua);
+}
+
 static ssize_t fsg_show_file(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
···
 	}
 	up_read(filesem);
 	return rc;
+}
+
+static ssize_t fsg_store_nofua(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t count)
+{
+	struct fsg_lun	*curlun = fsg_lun_from_dev(dev);
+	unsigned long	nofua;
+
+	if (strict_strtoul(buf, 2, &nofua))
+		return -EINVAL;
+
+	/* Sync data when switching from async mode to sync */
+	if (!nofua && curlun->nofua)
+		fsg_lun_fsync_sub(curlun);
+
+	curlun->nofua = nofua;
+
+	return count;
 }
 
 static ssize_t fsg_store_file(struct device *dev, struct device_attribute *attr,