usbip: Implement SG support to vhci-hcd and stub driver

There are bugs on vhci with usb 3.0 storage device. In USB, each SG
list entry buffer should be divisible by the bulk max packet size.
But with native SG support, this problem doesn't matter because the
SG buffer is treated as contiguous buffer. But without native SG
support, USB storage driver breaks SG list into several URBs and the
error occurs because of a buffer size of URB that cannot be divided
by the bulk max packet size. The error situation is as follows.

When USB Storage driver requests 31.5 KB data and has SG list which
has 3584 bytes buffer followed by 7 4096 bytes buffer for some
reason. USB Storage driver splits this SG list into several URBs
because VHCI doesn't support SG and sends them separately. So the
first URB buffer size is 3584 bytes. When receiving data from device,
USB 3.0 device sends data packet of 1024 bytes size because the max
packet size of BULK pipe is 1024 bytes. So device sends 4096 bytes.
But the first URB buffer has only 3584 bytes buffer size. So host
controller terminates the transfer even though there is more data to
receive. So, vhci needs to support SG transfer to prevent this error.

In this patch, vhci supports SG regardless of whether the server's
host controller supports SG or not, because stub driver splits SG
list into several URBs if the server's host controller doesn't
support SG.

To support SG, vhci sets URB_DMA_MAP_SG flag in urb->transfer_flags
if URB has SG list and this flag will tell stub driver to use SG
list. After receiving urb from stub driver, vhci clear URB_DMA_MAP_SG
flag to avoid unnecessary DMA unmapping in HCD.

vhci sends each SG list entry to stub driver. Then, stub driver sees
the total length of the buffer and allocates SG table and pages
according to the total buffer length calling sgl_alloc(). After stub
driver receives completed URB, it again sends each SG list entry to
vhci.

If the server's host controller doesn't support SG, stub driver
breaks a single SG request into several URBs and submits them to
the server's host controller. When all the split URBs are completed,
stub driver reassembles the URBs into a single return command and
sends it to vhci.

Moreover, in the situation where vhci supports SG, but stub driver
does not, or vice versa, usbip works normally. Because there is no
protocol modification, there is no problem in communication between
server and client even if the one has a kernel without SG support.

In the case of vhci supports SG and stub driver doesn't, because
vhci sends only the total length of the buffer to stub driver as
it did before the patch applied, stub driver only needs to allocate
the required length of buffers using only kmalloc() regardless of
whether vhci supports SG or not. But stub driver has to allocate
buffer with kmalloc() as much as the total length of SG buffer which
is quite huge when vhci sends SG request, so it has overhead in
buffer allocation in this situation.

If stub driver needs to send data buffer to vhci because of IN pipe,
stub driver also sends only total length of buffer as metadata and
then sends real data as vhci does. Then vhci receive data from stub
driver and store it to the corresponding buffer of SG list entry.

And for the case of stub driver supports SG and vhci doesn't, since
the USB storage driver checks that vhci doesn't support SG and sends
the request to stub driver by splitting the SG list into multiple
URBs, stub driver allocates a buffer for each URB with kmalloc() as
it did before this patch.

* Test environment

Test uses two difference machines and two different kernel version
to make mismatch situation between the client and the server where
vhci supports SG, but stub driver does not, or vice versa. All tests
are conducted in both full SG support that both vhci and stub support
SG and half SG support that is the mismatch situation. Test kernel
version is 5.3-rc6 with commit "usb: add a HCD_DMA flag instead of
guestimating DMA capabilities" to avoid unnecessary DMA mapping and
unmapping.

- Test kernel version
- 5.3-rc6 with SG support
- 5.1.20-200.fc29.x86_64 without SG support

* SG support test

- Test devices
- Super-speed storage device - SanDisk Ultra USB 3.0
- High-speed storage device - SMI corporation USB 2.0 flash drive

- Test description

Test read and write operation of mass storage device that uses the
BULK transfer. In test, the client reads and writes files whose size
is over 1G and it works normally.

* Regression test

- Test devices
- Super-speed device - Logitech Brio webcam
- High-speed device - Logitech C920 HD Pro webcam
- Full-speed device - Logitech bluetooth mouse
- Britz BR-Orion speaker
- Low-speed device - Logitech wired mouse

- Test description

Moving and click test for mouse. To test the webcam, use gnome-cheese.
To test the speaker, play music and video on the client. All works
normally.

* VUDC compatibility test

VUDC also works well with this patch. Tests are done with two USB
gadget created by CONFIGFS USB gadget. Both use the BULK pipe.

1. Serial gadget
2. Mass storage gadget

- Serial gadget test

Serial gadget on the host sends and receives data using cat command
on the /dev/ttyGS<N>. The client uses minicom to communicate with
the serial gadget.

- Mass storage gadget test

After connecting the gadget with vhci, use "dd" to test read and
write operation on the client side.

Read - dd if=/dev/sd<N> iflag=direct of=/dev/null bs=1G count=1
Write - dd if=<my file path> iflag=direct of=/dev/sd<N> bs=1G count=1

Signed-off-by: Suwan Kim <[e-mail]>
Acked-by: Shuah khan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/usbip/stub.h

···
 	unsigned long seqnum;
 	struct list_head list;
 	struct stub_device *sdev;
-	struct urb *urb;
+	struct urb **urbs;
+	struct scatterlist *sgl;
+	int num_urbs;
+	int completed_urbs;
+	int urb_status;
 
 	int unlinking;
 };
···
 struct bus_id_priv *get_busid_priv(const char *busid);
 void put_busid_priv(struct bus_id_priv *bid);
 int del_match_busid(char *busid);
+void stub_free_priv_and_urb(struct stub_priv *priv);
 void stub_device_cleanup_urbs(struct stub_device *sdev);
 
 /* stub_rx.c */

drivers/usb/usbip/stub_main.c

···
 #include <linux/string.h>
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
···
 	struct stub_priv *priv, *tmp;
 
 	list_for_each_entry_safe(priv, tmp, listhead, list) {
-		list_del(&priv->list);
+		list_del_init(&priv->list);
 		return priv;
 	}
 
 	return NULL;
+}
+
+void stub_free_priv_and_urb(struct stub_priv *priv)
+{
+	struct urb *urb;
+	int i;
+
+	for (i = 0; i < priv->num_urbs; i++) {
+		urb = priv->urbs[i];
+
+		if (!urb)
+			return;
+
+		kfree(urb->setup_packet);
+		urb->setup_packet = NULL;
+
+
+		if (urb->transfer_buffer && !priv->sgl) {
+			kfree(urb->transfer_buffer);
+			urb->transfer_buffer = NULL;
+		}
+
+		if (urb->num_sgs) {
+			sgl_free(urb->sg);
+			urb->sg = NULL;
+			urb->num_sgs = 0;
+		}
+
+		usb_free_urb(urb);
+	}
+	if (!list_empty(&priv->list))
+		list_del(&priv->list);
+	if (priv->sgl)
+		sgl_free(priv->sgl);
+	kfree(priv->urbs);
+	kmem_cache_free(stub_priv_cache, priv);
 }
 
 static struct stub_priv *stub_priv_pop(struct stub_device *sdev)
···
 void stub_device_cleanup_urbs(struct stub_device *sdev)
 {
 	struct stub_priv *priv;
-	struct urb *urb;
+	int i;
 
 	dev_dbg(&sdev->udev->dev, "Stub device cleaning up urbs\n");
 
 	while ((priv = stub_priv_pop(sdev))) {
-		urb = priv->urb;
-		dev_dbg(&sdev->udev->dev, "free urb seqnum %lu\n",
-			priv->seqnum);
-		usb_kill_urb(urb);
+		for (i = 0; i < priv->num_urbs; i++)
+			usb_kill_urb(priv->urbs[i]);
 
-		kmem_cache_free(stub_priv_cache, priv);
-
-		kfree(urb->transfer_buffer);
-		urb->transfer_buffer = NULL;
-
-		kfree(urb->setup_packet);
-		urb->setup_packet = NULL;
-
-		usb_free_urb(urb);
+		stub_free_priv_and_urb(priv);
 	}
 }
 

drivers/usb/usbip/stub_rx.c

···
 #include <linux/kthread.h>
 #include <linux/usb.h>
 #include <linux/usb/hcd.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
···
 static int stub_recv_cmd_unlink(struct stub_device *sdev,
 				struct usbip_header *pdu)
 {
-	int ret;
+	int ret, i;
 	unsigned long flags;
 	struct stub_priv *priv;
 
···
 		 * so a driver in a client host will know the failure
 		 * of the unlink request ?
 		 */
-		ret = usb_unlink_urb(priv->urb);
-		if (ret != -EINPROGRESS)
-			dev_err(&priv->urb->dev->dev,
-				"failed to unlink a urb # %lu, ret %d\n",
-				priv->seqnum, ret);
-
+		for (i = priv->completed_urbs; i < priv->num_urbs; i++) {
+			ret = usb_unlink_urb(priv->urbs[i]);
+			if (ret != -EINPROGRESS)
+				dev_err(&priv->urbs[i]->dev->dev,
+					"failed to unlink %d/%d urb of seqnum %lu, ret %d\n",
+					i + 1, priv->num_urbs,
+					priv->seqnum, ret);
+		}
 		return 0;
 	}
 
···
 	urb->transfer_flags &= allowed;
 }
 
+static int stub_recv_xbuff(struct usbip_device *ud, struct stub_priv *priv)
+{
+	int ret;
+	int i;
+
+	for (i = 0; i < priv->num_urbs; i++) {
+		ret = usbip_recv_xbuff(ud, priv->urbs[i]);
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}
+
 static void stub_recv_cmd_submit(struct stub_device *sdev,
 				 struct usbip_header *pdu)
 {
-	int ret;
 	struct stub_priv *priv;
 	struct usbip_device *ud = &sdev->ud;
 	struct usb_device *udev = sdev->udev;
+	struct scatterlist *sgl = NULL, *sg;
+	void *buffer = NULL;
+	unsigned long long buf_len;
+	int nents;
+	int num_urbs = 1;
 	int pipe = get_pipe(sdev, pdu);
+	int use_sg = pdu->u.cmd_submit.transfer_flags & URB_DMA_MAP_SG;
+	int support_sg = 1;
+	int np = 0;
+	int ret, i;
 
 	if (pipe == -1)
 		return;
···
 	if (!priv)
 		return;
 
-	/* setup a urb */
-	if (usb_pipeisoc(pipe))
-		priv->urb = usb_alloc_urb(pdu->u.cmd_submit.number_of_packets,
-					  GFP_KERNEL);
-	else
-		priv->urb = usb_alloc_urb(0, GFP_KERNEL);
-
-	if (!priv->urb) {
-		usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
-		return;
-	}
+	buf_len = (unsigned long long)pdu->u.cmd_submit.transfer_buffer_length;
 
 	/* allocate urb transfer buffer, if needed */
-	if (pdu->u.cmd_submit.transfer_buffer_length > 0) {
-		priv->urb->transfer_buffer =
-			kzalloc(pdu->u.cmd_submit.transfer_buffer_length,
-				GFP_KERNEL);
-		if (!priv->urb->transfer_buffer) {
-			usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
-			return;
+	if (buf_len) {
+		if (use_sg) {
+			sgl = sgl_alloc(buf_len, GFP_KERNEL, &nents);
+			if (!sgl)
+				goto err_malloc;
+		} else {
+			buffer = kzalloc(buf_len, GFP_KERNEL);
+			if (!buffer)
+				goto err_malloc;
 		}
 	}
 
-	/* copy urb setup packet */
-	priv->urb->setup_packet = kmemdup(&pdu->u.cmd_submit.setup, 8,
-					  GFP_KERNEL);
-	if (!priv->urb->setup_packet) {
-		dev_err(&udev->dev, "allocate setup_packet\n");
-		usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
-		return;
+	/* Check if the server's HCD supports SG */
+	if (use_sg && !udev->bus->sg_tablesize) {
+		/*
+		 * If the server's HCD doesn't support SG, break a single SG
+		 * request into several URBs and map each SG list entry to
+		 * corresponding URB buffer. The previously allocated SG
+		 * list is stored in priv->sgl (If the server's HCD support SG,
+		 * SG list is stored only in urb->sg) and it is used as an
+		 * indicator that the server split single SG request into
+		 * several URBs. Later, priv->sgl is used by stub_complete() and
+		 * stub_send_ret_submit() to reassemble the divied URBs.
+		 */
+		support_sg = 0;
+		num_urbs = nents;
+		priv->completed_urbs = 0;
+		pdu->u.cmd_submit.transfer_flags &= ~URB_DMA_MAP_SG;
 	}
 
-	/* set other members from the base header of pdu */
-	priv->urb->context                = (void *) priv;
-	priv->urb->dev                    = udev;
-	priv->urb->pipe                   = pipe;
-	priv->urb->complete               = stub_complete;
+	/* allocate urb array */
+	priv->num_urbs = num_urbs;
+	priv->urbs = kmalloc_array(num_urbs, sizeof(*priv->urbs), GFP_KERNEL);
+	if (!priv->urbs)
+		goto err_urbs;
 
-	usbip_pack_pdu(pdu, priv->urb, USBIP_CMD_SUBMIT, 0);
+	/* setup a urb */
+	if (support_sg) {
+		if (usb_pipeisoc(pipe))
+			np = pdu->u.cmd_submit.number_of_packets;
 
+		priv->urbs[0] = usb_alloc_urb(np, GFP_KERNEL);
+		if (!priv->urbs[0])
+			goto err_urb;
 
-	if (usbip_recv_xbuff(ud, priv->urb) < 0)
+		if (buf_len) {
+			if (use_sg) {
+				priv->urbs[0]->sg = sgl;
+				priv->urbs[0]->num_sgs = nents;
+				priv->urbs[0]->transfer_buffer = NULL;
+			} else {
+				priv->urbs[0]->transfer_buffer = buffer;
+			}
+		}
+
+		/* copy urb setup packet */
+		priv->urbs[0]->setup_packet = kmemdup(&pdu->u.cmd_submit.setup,
+					8, GFP_KERNEL);
+		if (!priv->urbs[0]->setup_packet) {
+			usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
+			return;
+		}
+
+		usbip_pack_pdu(pdu, priv->urbs[0], USBIP_CMD_SUBMIT, 0);
+	} else {
+		for_each_sg(sgl, sg, nents, i) {
+			priv->urbs[i] = usb_alloc_urb(0, GFP_KERNEL);
+			/* The URBs which is previously allocated will be freed
+			 * in stub_device_cleanup_urbs() if error occurs.
+			 */
+			if (!priv->urbs[i])
+				goto err_urb;
+
+			usbip_pack_pdu(pdu, priv->urbs[i], USBIP_CMD_SUBMIT, 0);
+			priv->urbs[i]->transfer_buffer = sg_virt(sg);
+			priv->urbs[i]->transfer_buffer_length = sg->length;
+		}
+		priv->sgl = sgl;
+	}
+
+	for (i = 0; i < num_urbs; i++) {
+		/* set other members from the base header of pdu */
+		priv->urbs[i]->context = (void *) priv;
+		priv->urbs[i]->dev = udev;
+		priv->urbs[i]->pipe = pipe;
+		priv->urbs[i]->complete = stub_complete;
+
+		/* no need to submit an intercepted request, but harmless? */
+		tweak_special_requests(priv->urbs[i]);
+
+		masking_bogus_flags(priv->urbs[i]);
+	}
+
+	if (stub_recv_xbuff(ud, priv) < 0)
 		return;
 
-	if (usbip_recv_iso(ud, priv->urb) < 0)
+	if (usbip_recv_iso(ud, priv->urbs[0]) < 0)
 		return;
 
-	/* no need to submit an intercepted request, but harmless? */
-	tweak_special_requests(priv->urb);
-
-	masking_bogus_flags(priv->urb);
 	/* urb is now ready to submit */
-	ret = usb_submit_urb(priv->urb, GFP_KERNEL);
+	for (i = 0; i < priv->num_urbs; i++) {
+		ret = usb_submit_urb(priv->urbs[i], GFP_KERNEL);
 
-	if (ret == 0)
-		usbip_dbg_stub_rx("submit urb ok, seqnum %u\n",
-				  pdu->base.seqnum);
-	else {
-		dev_err(&udev->dev, "submit_urb error, %d\n", ret);
-		usbip_dump_header(pdu);
-		usbip_dump_urb(priv->urb);
+		if (ret == 0)
+			usbip_dbg_stub_rx("submit urb ok, seqnum %u\n",
+					pdu->base.seqnum);
+		else {
+			dev_err(&udev->dev, "submit_urb error, %d\n", ret);
+			usbip_dump_header(pdu);
+			usbip_dump_urb(priv->urbs[i]);
 
-		/*
-		 * Pessimistic.
-		 * This connection will be discarded.
-		 */
-		usbip_event_add(ud, SDEV_EVENT_ERROR_SUBMIT);
+			/*
+			 * Pessimistic.
+			 * This connection will be discarded.
+			 */
+			usbip_event_add(ud, SDEV_EVENT_ERROR_SUBMIT);
+			break;
+		}
 	}
 
 	usbip_dbg_stub_rx("Leave\n");
+	return;
+
+err_urb:
+	kfree(priv->urbs);
+err_urbs:
+	kfree(buffer);
+	sgl_free(sgl);
+err_malloc:
+	usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
 }
 
 /* recv a pdu */

drivers/usb/usbip/stub_tx.c

···
 
 #include <linux/kthread.h>
 #include <linux/socket.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
-
-static void stub_free_priv_and_urb(struct stub_priv *priv)
-{
-	struct urb *urb = priv->urb;
-
-	kfree(urb->setup_packet);
-	urb->setup_packet = NULL;
-
-	kfree(urb->transfer_buffer);
-	urb->transfer_buffer = NULL;
-
-	list_del(&priv->list);
-	kmem_cache_free(stub_priv_cache, priv);
-	usb_free_urb(urb);
-}
 
 /* be in spin_lock_irqsave(&sdev->priv_lock, flags) */
 void stub_enqueue_ret_unlink(struct stub_device *sdev, __u32 seqnum,
···
 			 "urb completion with non-zero status %d\n",
 			 urb->status);
 		break;
+	}
+
+	/*
+	 * If the server breaks single SG request into the several URBs, the
+	 * URBs must be reassembled before sending completed URB to the vhci.
+	 * Don't wake up the tx thread until all the URBs are completed.
+	 */
+	if (priv->sgl) {
+		priv->completed_urbs++;
+
+		/* Only save the first error status */
+		if (urb->status && !priv->urb_status)
+			priv->urb_status = urb->status;
+
+		if (priv->completed_urbs < priv->num_urbs)
+			return;
 	}
 
 	/* link a urb to the queue of tx. */
···
 	size_t total_size = 0;
 
 	while ((priv = dequeue_from_priv_tx(sdev)) != NULL) {
-		int ret;
-		struct urb *urb = priv->urb;
+		struct urb *urb = priv->urbs[0];
 		struct usbip_header pdu_header;
 		struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 		struct kvec *iov = NULL;
+		struct scatterlist *sg;
+		u32 actual_length = 0;
 		int iovnum = 0;
+		int ret;
+		int i;
 
 		txsize = 0;
 		memset(&pdu_header, 0, sizeof(pdu_header));
 		memset(&msg, 0, sizeof(msg));
 
-		if (urb->actual_length > 0 && !urb->transfer_buffer) {
+		if (urb->actual_length > 0 && !urb->transfer_buffer &&
+		   !urb->num_sgs) {
 			dev_err(&sdev->udev->dev,
 				"urb: actual_length %d transfer_buffer null\n",
 				urb->actual_length);
···
 
 		if (usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS)
 			iovnum = 2 + urb->number_of_packets;
+		else if (usb_pipein(urb->pipe) && urb->actual_length > 0 &&
+			urb->num_sgs)
+			iovnum = 1 + urb->num_sgs;
+		else if (usb_pipein(urb->pipe) && priv->sgl)
+			iovnum = 1 + priv->num_urbs;
 		else
 			iovnum = 2;
 
···
 		setup_ret_submit_pdu(&pdu_header, urb);
 		usbip_dbg_stub_tx("setup txdata seqnum: %d\n",
 				  pdu_header.base.seqnum);
+
+		if (priv->sgl) {
+			for (i = 0; i < priv->num_urbs; i++)
+				actual_length += priv->urbs[i]->actual_length;
+
+			pdu_header.u.ret_submit.status = priv->urb_status;
+			pdu_header.u.ret_submit.actual_length = actual_length;
+		}
+
 		usbip_header_correct_endian(&pdu_header, 1);
 
 		iov[iovnum].iov_base = &pdu_header;
···
 		txsize += sizeof(pdu_header);
 
 		/* 2. setup transfer buffer */
-		if (usb_pipein(urb->pipe) &&
+		if (usb_pipein(urb->pipe) && priv->sgl) {
+			/* If the server split a single SG request into several
+			 * URBs because the server's HCD doesn't support SG,
+			 * reassemble the split URB buffers into a single
+			 * return command.
+			 */
+			for (i = 0; i < priv->num_urbs; i++) {
+				iov[iovnum].iov_base =
+					priv->urbs[i]->transfer_buffer;
+				iov[iovnum].iov_len =
+					priv->urbs[i]->actual_length;
+				iovnum++;
+			}
+			txsize += actual_length;
+		} else if (usb_pipein(urb->pipe) &&
 		    usb_pipetype(urb->pipe) != PIPE_ISOCHRONOUS &&
 		    urb->actual_length > 0) {
-			iov[iovnum].iov_base = urb->transfer_buffer;
-			iov[iovnum].iov_len  = urb->actual_length;
-			iovnum++;
+			if (urb->num_sgs) {
+				unsigned int copy = urb->actual_length;
+				int size;
+
+				for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+					if (copy == 0)
+						break;
+
+					if (copy < sg->length)
+						size = copy;
+					else
+						size = sg->length;
+
+					iov[iovnum].iov_base = sg_virt(sg);
+					iov[iovnum].iov_len = size;
+
+					iovnum++;
+					copy -= size;
+				}
+			} else {
+				iov[iovnum].iov_base = urb->transfer_buffer;
+				iov[iovnum].iov_len  = urb->actual_length;
+				iovnum++;
+			}
 			txsize += urb->actual_length;
 		} else if (usb_pipein(urb->pipe) &&
 			   usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS) {

drivers/usb/usbip/usbip_common.c

···
 /* some members of urb must be substituted before. */
 int usbip_recv_xbuff(struct usbip_device *ud, struct urb *urb)
 {
-	int ret;
+	struct scatterlist *sg;
+	int ret = 0;
+	int recv;
 	int size;
+	int copy;
+	int i;
 
 	if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC) {
 		/* the direction of urb must be OUT. */
···
 	if (!(size > 0))
 		return 0;
 
-	if (size > urb->transfer_buffer_length) {
+	if (size > urb->transfer_buffer_length)
 		/* should not happen, probably malicious packet */
-		if (ud->side == USBIP_STUB) {
-			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
-			return 0;
-		} else {
-			usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
-			return -EPIPE;
-		}
-	}
+		goto error;
 
-	ret = usbip_recv(ud->tcp_socket, urb->transfer_buffer, size);
-	if (ret != size) {
-		dev_err(&urb->dev->dev, "recv xbuf, %d\n", ret);
-		if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC) {
-			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
-		} else {
-			usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
-			return -EPIPE;
+	if (urb->num_sgs) {
+		copy = size;
+		for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+			int recv_size;
+
+			if (copy < sg->length)
+				recv_size = copy;
+			else
+				recv_size = sg->length;
+
+			recv = usbip_recv(ud->tcp_socket, sg_virt(sg),
+						recv_size);
+
+			if (recv != recv_size)
+				goto error;
+
+			copy -= recv;
+			ret += recv;
 		}
+
+		if (ret != size)
+			goto error;
+	} else {
+		ret = usbip_recv(ud->tcp_socket, urb->transfer_buffer, size);
+		if (ret != size)
+			goto error;
 	}
 
 	return ret;
+
+error:
+	dev_err(&urb->dev->dev, "recv xbuf, %d\n", ret);
+	if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC)
+		usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
+	else
+		usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
+
+	return -EPIPE;
 }
 EXPORT_SYMBOL_GPL(usbip_recv_xbuff);
 

drivers/usb/usbip/vhci_hcd.c

···
 	}
 	vdev = &vhci_hcd->vdev[portnum-1];
 
-	if (!urb->transfer_buffer && urb->transfer_buffer_length) {
+	if (!urb->transfer_buffer && !urb->num_sgs &&
+	     urb->transfer_buffer_length) {
 		dev_dbg(dev, "Null URB transfer buffer\n");
 		return -EINVAL;
 	}
···
 		hcd->speed = HCD_USB3;
 		hcd->self.root_hub->speed = USB_SPEED_SUPER;
 	}
+
+	/*
+	 * Support SG.
+	 * sg_tablesize is an arbitrary value to alleviate memory pressure
+	 * on the host.
+	 */
+	hcd->self.sg_tablesize = 32;
+	hcd->self.no_sg_constraint = 1;
+
 	return 0;
 }
 

drivers/usb/usbip/vhci_rx.c

···
 	if (usbip_dbg_flag_vhci_rx)
 		usbip_dump_urb(urb);
 
+	if (urb->num_sgs)
+		urb->transfer_flags &= ~URB_DMA_MAP_SG;
+
 	usbip_dbg_vhci_rx("now giveback urb %u\n", pdu->base.seqnum);
 
 	spin_lock_irqsave(&vhci->lock, flags);

drivers/usb/usbip/vhci_tx.c

···
 
 #include <linux/kthread.h>
 #include <linux/slab.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "vhci.h"
···
 
 static int vhci_send_cmd_submit(struct vhci_device *vdev)
 {
+	struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 	struct vhci_priv *priv = NULL;
+	struct scatterlist *sg;
 
 	struct msghdr msg;
-	struct kvec iov[3];
+	struct kvec *iov;
 	size_t txsize;
 
 	size_t total_size = 0;
+	int iovnum;
+	int err = -ENOMEM;
+	int i;
 
 	while ((priv = dequeue_from_priv_tx(vdev)) != NULL) {
 		int ret;
 		struct urb *urb = priv->urb;
 		struct usbip_header pdu_header;
-		struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 
 		txsize = 0;
 		memset(&pdu_header, 0, sizeof(pdu_header));
···
 		usbip_dbg_vhci_tx("setup txdata urb seqnum %lu\n",
 				  priv->seqnum);
 
+		if (urb->num_sgs && usb_pipeout(urb->pipe))
+			iovnum = 2 + urb->num_sgs;
+		else
+			iovnum = 3;
+
+		iov = kcalloc(iovnum, sizeof(*iov), GFP_KERNEL);
+		if (!iov) {
+			usbip_event_add(&vdev->ud, SDEV_EVENT_ERROR_MALLOC);
+			return -ENOMEM;
+		}
+
+		if (urb->num_sgs)
+			urb->transfer_flags |= URB_DMA_MAP_SG;
+
 		/* 1. setup usbip_header */
 		setup_cmd_submit_pdu(&pdu_header, urb);
 		usbip_header_correct_endian(&pdu_header, 1);
+		iovnum = 0;
 
-		iov[0].iov_base = &pdu_header;
-		iov[0].iov_len  = sizeof(pdu_header);
+		iov[iovnum].iov_base = &pdu_header;
+		iov[iovnum].iov_len  = sizeof(pdu_header);
 		txsize += sizeof(pdu_header);
+		iovnum++;
 
 		/* 2. setup transfer buffer */
 		if (!usb_pipein(urb->pipe) && urb->transfer_buffer_length > 0) {
-			iov[1].iov_base = urb->transfer_buffer;
-			iov[1].iov_len  = urb->transfer_buffer_length;
+			if (urb->num_sgs &&
+				      !usb_endpoint_xfer_isoc(&urb->ep->desc)) {
+				for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+					iov[iovnum].iov_base = sg_virt(sg);
+					iov[iovnum].iov_len = sg->length;
+					iovnum++;
+				}
+			} else {
+				iov[iovnum].iov_base = urb->transfer_buffer;
+				iov[iovnum].iov_len  =
+						urb->transfer_buffer_length;
+				iovnum++;
+			}
 			txsize += urb->transfer_buffer_length;
 		}
 
···
 			if (!iso_buffer) {
 				usbip_event_add(&vdev->ud,
 						SDEV_EVENT_ERROR_MALLOC);
-				return -1;
+				goto err_iso_buffer;
 			}
 
-			iov[2].iov_base = iso_buffer;
-			iov[2].iov_len  = len;
+			iov[iovnum].iov_base = iso_buffer;
+			iov[iovnum].iov_len  = len;
+			iovnum++;
 			txsize += len;
 		}
 
-		ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, 3, txsize);
+		ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, iovnum,
+				     txsize);
 		if (ret != txsize) {
 			pr_err("sendmsg failed!, ret=%d for %zd\n", ret,
 			       txsize);
-			kfree(iso_buffer);
 			usbip_event_add(&vdev->ud, VDEV_EVENT_ERROR_TCP);
-			return -1;
+			err = -EPIPE;
+			goto err_tx;
 		}
 
+		kfree(iov);
 		kfree(iso_buffer);
 		usbip_dbg_vhci_tx("send txdata\n");
 
···
 	}
 
 	return total_size;
+
+err_tx:
+	kfree(iso_buffer);
+err_iso_buffer:
+	kfree(iov);
+
+	return err;
 }
 
 static struct vhci_unlink *dequeue_from_unlink_tx(struct vhci_device *vdev)