[PATCH v2 4/4] tools: usb: p9_fwd: add usb gadget packet forwarder script

[Michael Grzeschik <m.grzeschik@pengutronix.de>]

This patch is adding an small python tool to forward 9pfs requests
from the USB gadget to an existing 9pfs TCP server. Since currently all
9pfs servers lack support for the usb transport this tool is an useful
helper to get started.

Refer the Documentation section "USBG Example" in
Documentation/filesystems/9p.rst on how to use it.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

---
v1 -> v2:
  - added usbg 9pfs detailed instructions to 9p.rst doc
---
 Documentation/filesystems/9p.rst |  32 +++++++
 tools/usb/p9_fwd.py              | 194 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 226 insertions(+)

diff --git a/Documentation/filesystems/9p.rst b/Documentation/filesystems/9p.rst
index 64439068a8fc5..264265c72ba67 100644
--- a/Documentation/filesystems/9p.rst
+++ b/Documentation/filesystems/9p.rst
@@ -67,6 +67,38 @@ To mount a 9p FS on a USB Host accessible via the gadget as root filesystem::
 where mount_tag is the tag associated by the usb gadget transport. The
 pattern is usb9pfs0, usb9pfs1, ...
 
+USBG Example
+============
+
+The USB host exports a filesystem, while the gadget on the USB device
+side makes it mountable.
+
+Diod (9pfs server) and the forwarder are on the development host, where
+the root filesystem is actually stored. The gadget is initialized during
+boot (or later) on the embedded board. Then the forwarder will find it
+on the USB bus and start forwarding requests.
+
+In this case the 9p requests come from the device and are handled by the
+host. The reason is that USB device ports are normally not available on
+PCs, so a connection in the other direction would not work.
+
+When using the usbg transport, for now there is no native usb host
+service capable to handle the requests from the gadget driver. For
+this we have to use the extra python tool p9_fwd.py from tools/usb.
+
+Just start the 9pfs capable network server like diod/nfs-ganesha e.g.:
+
+	$ diod -f -n -d 0 -S -l 0.0.0.0:9999 -e $PWD
+
+Then start the python transport:
+
+	$ python $kernel_dir/tools/usb/p9_fwd.py -p 9999
+
+After that the gadget driver can be used as described above.
+
+One use-case is to use it as an alternative to NFS root booting during
+the development of embedded Linux devices.
+
 Options
 =======
 
diff --git a/tools/usb/p9_fwd.py b/tools/usb/p9_fwd.py
new file mode 100755
index 0000000000000..95208df11abef
--- /dev/null
+++ b/tools/usb/p9_fwd.py
@@ -0,0 +1,194 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import argparse
+import errno
+import logging
+import socket
+import struct
+import sys
+import time
+
+import usb.core
+import usb.util
+
+
+class Forwarder:
+    HEXDUMP_FILTER = (
+        "".join(chr(x).isprintable() and chr(x) or "." for x in range(128)) + "." * 128
+    )
+
+    @staticmethod
+    def _log_hexdump(data):
+        if not logging.root.isEnabledFor(logging.TRACE):
+            return
+        L = 16
+        for c in range(0, len(data), L):
+            chars = data[c : c + L]
+            dump = " ".join(f"{x:02x}" for x in chars)
+            printable = "".join(HEXDUMP_FILTER[x] for x in chars)
+            line = f"{c:08x}  {dump:{L*3}s} |{printable:{L}s}|"
+            logging.root.log(logging.TRACE, "%s", line)
+
+    def __init__(self, server):
+        self.stats = {
+            "c2s packets": 0,
+            "c2s bytes": 0,
+            "s2c packets": 0,
+            "s2c bytes": 0,
+        }
+        self.stats_logged = time.monotonic()
+
+        dev = usb.core.find(idVendor=0x1D6B, idProduct=0x0109)
+        if dev is None:
+            raise ValueError("Device not found")
+
+        logging.info(f"found device: {dev.bus}/{dev.address}")
+
+        # dev.set_configuration() is not necessary since g_multi has only one
+        usb9pfs = None
+        # g_multi adds 9pfs as last interface
+        cfg = dev.get_active_configuration()
+        for intf in cfg:
+            # we have to detach the usb-storage driver from multi gadget since
+            # stall option could be set, which will lead to spontaneous port
+            # resets and our transfers will run dead
+            if intf.bInterfaceClass == 0x08:
+                if dev.is_kernel_driver_active(intf.bInterfaceNumber):
+                    dev.detach_kernel_driver(intf.bInterfaceNumber)
+
+            if (
+                intf.bInterfaceClass == 0xFF
+                and intf.bInterfaceSubClass == 0xFF
+                and intf.bInterfaceProtocol == 0x09
+            ):
+                usb9pfs = intf
+        if usb9pfs is None:
+            raise ValueError("Interface not found")
+
+        logging.info(f"claiming interface:\n{usb9pfs}")
+        usb.util.claim_interface(dev, usb9pfs.bInterfaceNumber)
+        ep_out = usb.util.find_descriptor(
+            usb9pfs,
+            custom_match=lambda e: usb.util.endpoint_direction(e.bEndpointAddress)
+            == usb.util.ENDPOINT_OUT,
+        )
+        assert ep_out is not None
+        ep_in = usb.util.find_descriptor(
+            usb9pfs,
+            custom_match=lambda e: usb.util.endpoint_direction(e.bEndpointAddress)
+            == usb.util.ENDPOINT_IN,
+        )
+        assert ep_in is not None
+        logging.info(f"interface claimed")
+
+        self.ep_out = ep_out
+        self.ep_in = ep_in
+        self.dev = dev
+
+        # create and connect socket
+        self.s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.s.connect(server)
+
+        logging.info(f"connected to server")
+
+    def c2s(self):
+        """forward a request from the USB client to the TCP server"""
+        data = None
+        while data is None:
+            try:
+                logging.log(logging.TRACE, "c2s: reading")
+                data = self.ep_in.read(self.ep_in.wMaxPacketSize)
+            except usb.core.USBTimeoutError:
+                logging.log(logging.TRACE, "c2s: reading timed out")
+                continue
+            except usb.core.USBError as e:
+                if e.errno == errno.EIO:
+                    logging.debug("c2s: reading failed with %s, retrying", repr(e))
+                    time.sleep(0.5)
+                    continue
+                else:
+                    logging.error("c2s: reading failed with %s, aborting", repr(e))
+                    raise
+        size = struct.unpack("<I", data[:4])[0]
+        while len(data) < size:
+            data += self.ep_in.read(size - len(data))
+        logging.log(logging.TRACE, "c2s: writing")
+        self._log_hexdump(data)
+        self.s.send(data)
+        logging.debug("c2s: forwarded %i bytes", size)
+        self.stats["c2s packets"] += 1
+        self.stats["c2s bytes"] += size
+
+    def s2c(self):
+        """forward a response from the TCP server to the USB client"""
+        logging.log(logging.TRACE, "s2c: reading")
+        data = self.s.recv(4)
+        size = struct.unpack("<I", data[:4])[0]
+        while len(data) < size:
+            data += self.s.recv(size - len(data))
+        logging.log(logging.TRACE, "s2c: writing")
+        self._log_hexdump(data)
+        while data:
+            written = self.ep_out.write(data)
+            assert written > 0
+            data = data[written:]
+        if size % self.ep_out.wMaxPacketSize == 0:
+            logging.log(logging.TRACE, "sending zero length packet")
+            self.ep_out.write(b"")
+        logging.debug("s2c: forwarded %i bytes", size)
+        self.stats["s2c packets"] += 1
+        self.stats["s2c bytes"] += size
+
+    def log_stats(self):
+        logging.info("statistics:")
+        for k, v in self.stats.items():
+            logging.info(f"  {k+':':14s} {v}")
+
+    def log_stats_interval(self, interval=5):
+        if (time.monotonic() - self.stats_logged) < interval:
+            return
+
+        self.log_stats()
+        self.stats_logged = time.monotonic()
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Forward 9PFS requests from USB to TCP",
+    )
+
+    parser.add_argument(
+        "-s", "--server", type=str, default="127.0.0.1", help="server hostname"
+    )
+    parser.add_argument("-p", "--port", type=int, default=564, help="server port")
+    parser.add_argument("-v", "--verbose", action="count", default=0)
+
+    args = parser.parse_args()
+
+    logging.TRACE = logging.DEBUG - 5
+    logging.addLevelName(logging.TRACE, "TRACE")
+
+    if args.verbose >= 2:
+        level = logging.TRACE
+    elif args.verbose:
+        level = logging.DEBUG
+    else:
+        level = logging.INFO
+    logging.basicConfig(
+        level=level, format="%(asctime)-15s %(levelname)-8s %(message)s"
+    )
+
+    f = Forwarder(server=(args.server, args.port))
+
+    try:
+        while True:
+            f.c2s()
+            f.s2c()
+            f.log_stats_interval()
+    finally:
+        f.log_stats()
+
+
+if __name__ == "__main__":
+    main()

-- 
2.39.2