usbip: vudc: Add SysFS infrastructure for VUDC

Add sysfs attributes to allow controlling vudc from usbip tools.

dev_desc - device descriptor of current gadget. This is required to
	 be consisten with current usbip protocol and allow to list
	 exportable devices on given machine.

usbip_sockfd - allows to pass socket to kernel to start usbip transfer.

usbip_status - currnent status of device

This commit is a result of cooperation between Samsung R&D Institute
Poland and Open Operating Systems Student Society at University
of Warsaw (O2S3@UW) consisting of:

    Igor Kotrasinski <ikotrasinsk@gmail.com>
    Karol Kosik <karo9@interia.eu>
    Ewelina Kosmider <3w3lfin@gmail.com>
    Dawid Lazarczyk <lazarczyk.dawid@gmail.com>
    Piotr Szulc <ps347277@students.mimuw.edu.pl>

Tutor and project owner:
    Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Igor Kotrasinski <i.kotrasinsk@samsung.com>
Signed-off-by: Karol Kosik <karo9@interia.eu>
[Various bug fixes, improvements and commit msg update]
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/vudc_sysfs.c

+/*
+ * Copyright (C) 2015 Karol Kosik <karo9@interia.eu>
+ * Copyright (C) 2015-2016 Samsung Electronics
+ *               Igor Kotrasinski <i.kotrasinsk@samsung.com>
+ *               Krzysztof Opasiak <k.opasiak@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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/device.h>
+#include <linux/list.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/ch9.h>
+#include <linux/sysfs.h>
+#include <linux/kthread.h>
+#include <linux/byteorder/generic.h>
+
+#include "usbip_common.h"
+#include "vudc.h"
+
+#include <net/sock.h>
+
+/* called with udc->lock held */
+int get_gadget_descs(struct vudc *udc)
+{
+	struct vrequest *usb_req;
+	struct vep *ep0 = to_vep(udc->gadget.ep0);
+	struct usb_device_descriptor *ddesc = &udc->dev_desc;
+	struct usb_ctrlrequest req;
+	int ret;
+
+	if (!udc || !udc->driver || !udc->pullup)
+		return -EINVAL;
+
+	req.bRequestType = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;
+	req.bRequest = USB_REQ_GET_DESCRIPTOR;
+	req.wValue = cpu_to_le16(USB_DT_DEVICE << 8);
+	req.wIndex = cpu_to_le16(0);
+	req.wLength = cpu_to_le16(sizeof(*ddesc));
+
+	spin_unlock(&udc->lock);
+	ret = udc->driver->setup(&(udc->gadget), &req);
+	spin_lock(&udc->lock);
+	if (ret < 0)
+		goto out;
+
+	/* assuming request queue is empty; request is now on top */
+	usb_req = list_last_entry(&ep0->req_queue, struct vrequest, req_entry);
+	list_del(&usb_req->req_entry);
+
+	if (usb_req->req.length > sizeof(*ddesc)) {
+		ret = -EOVERFLOW;
+		goto giveback_req;
+	}
+
+	memcpy(ddesc, usb_req->req.buf, sizeof(*ddesc));
+	udc->desc_cached = 1;
+	ret = 0;
+giveback_req:
+	usb_req->req.status = 0;
+	usb_req->req.actual = usb_req->req.length;
+	usb_gadget_giveback_request(&(ep0->ep), &(usb_req->req));
+out:
+	return ret;
+}
+
+/*
+ * Exposes device descriptor from the gadget driver.
+ */
+static ssize_t dev_desc_show(struct device *dev,
+			       struct device_attribute *attr, char *out)
+{
+	struct vudc *udc = (struct vudc *)dev_get_drvdata(dev);
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&udc->lock, flags);
+	if (!udc->desc_cached) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+
+	memcpy(out, &udc->dev_desc, sizeof(udc->dev_desc));
+	ret = sizeof(udc->dev_desc);
+unlock:
+	spin_unlock_irqrestore(&udc->lock, flags);
+	return ret;
+}
+static DEVICE_ATTR_RO(dev_desc);
+
+static ssize_t store_sockfd(struct device *dev, struct device_attribute *attr,
+		     const char *in, size_t count)
+{
+	struct vudc *udc = (struct vudc *) dev_get_drvdata(dev);
+	int rv;
+	int sockfd = 0;
+	int err;
+	struct socket *socket;
+	unsigned long flags;
+	int ret;
+
+	rv = kstrtoint(in, 0, &sockfd);
+	if (rv != 0)
+		return -EINVAL;
+
+	spin_lock_irqsave(&udc->lock, flags);
+	/* Don't export what we don't have */
+	if (!udc || !udc->driver || !udc->pullup) {
+		dev_err(dev, "no device or gadget not bound");
+		ret = -ENODEV;
+		goto unlock;
+	}
+
+	if (sockfd != -1) {
+		if (udc->connected) {
+			dev_err(dev, "Device already connected");
+			ret = -EBUSY;
+			goto unlock;
+		}
+
+		spin_lock_irq(&udc->ud.lock);
+
+		if (udc->ud.status != SDEV_ST_AVAILABLE) {
+			ret = -EINVAL;
+			goto unlock_ud;
+		}
+
+		socket = sockfd_lookup(sockfd, &err);
+		if (!socket) {
+			dev_err(dev, "failed to lookup sock");
+			ret = -EINVAL;
+			goto unlock_ud;
+		}
+
+		udc->ud.tcp_socket = socket;
+
+		spin_unlock_irq(&udc->ud.lock);
+		spin_unlock_irqrestore(&udc->lock, flags);
+
+		udc->ud.tcp_rx = kthread_get_run(&v_rx_loop,
+						    &udc->ud, "vudc_rx");
+		udc->ud.tcp_tx = kthread_get_run(&v_tx_loop,
+						    &udc->ud, "vudc_tx");
+
+		spin_lock_irqsave(&udc->lock, flags);
+		spin_lock_irq(&udc->ud.lock);
+		udc->ud.status = SDEV_ST_USED;
+		spin_unlock_irq(&udc->ud.lock);
+
+		do_gettimeofday(&udc->start_time);
+		v_start_timer(udc);
+		udc->connected = 1;
+	} else {
+		if (!udc->connected) {
+			dev_err(dev, "Device not connected");
+			ret = -EINVAL;
+			goto unlock;
+		}
+
+		spin_lock_irq(&udc->ud.lock);
+		if (udc->ud.status != SDEV_ST_USED) {
+			ret = -EINVAL;
+			goto unlock_ud;
+		}
+		spin_unlock_irq(&udc->ud.lock);
+
+		usbip_event_add(&udc->ud, VUDC_EVENT_DOWN);
+	}
+
+	spin_unlock_irqrestore(&udc->lock, flags);
+
+	return count;
+
+unlock_ud:
+	spin_unlock_irq(&udc->ud.lock);
+unlock:
+	spin_unlock_irqrestore(&udc->lock, flags);
+
+	return ret;
+}
+static DEVICE_ATTR(usbip_sockfd, S_IWUSR, NULL, store_sockfd);
+
+static ssize_t usbip_status_show(struct device *dev,
+			       struct device_attribute *attr, char *out)
+{
+	struct vudc *udc = (struct vudc *) dev_get_drvdata(dev);
+	int status;
+
+	if (!udc) {
+		dev_err(&udc->pdev->dev, "no device");
+		return -ENODEV;
+	}
+	spin_lock_irq(&udc->ud.lock);
+	status = udc->ud.status;
+	spin_unlock_irq(&udc->ud.lock);
+
+	return snprintf(out, PAGE_SIZE, "%d\n", status);
+}
+static DEVICE_ATTR_RO(usbip_status);
+
+static struct attribute *dev_attrs[] = {
+	&dev_attr_dev_desc.attr,
+	&dev_attr_usbip_sockfd.attr,
+	&dev_attr_usbip_status.attr,
+	NULL,
+};
+
+const struct attribute_group vudc_attr_group = {
+	.attrs = dev_attrs,
+};