chardev connection

host/dmctl/connection.py

@@ -5,6 +5,7 @@ import array
 import os
 import re
 import struct
+import sys
 
 import abc
 from typing import *
@@ -16,16 +17,17 @@ from typing import *
 
 
 class DevConn:
+    _VER_MIN = 0x0010
+    _VER_MAX = 0x00ff  # ???
+
     pass
 
+
 class UsbConn(DevConn):
     _USB_DEFAULT_VID = 0xcafe
     _USB_DEFAULT_PID = 0x1312
     _SUBCLASS = 42
     _PROTOCOL = 69
-    _VER_MIN = 0x0010
-    _VER_MAX = 0x00ff  # ???
-
     def _open_dev(dev) -> Union[UsbConn, str]:
         import usb, usb.core
 
@@ -61,20 +63,21 @@ class UsbConn(DevConn):
             # is in use by something else
             epout.write(b'\x00')
             resp = epin.read(4)
-            if resp[0] != 0 or resp[1] != 2:
-                return "Device does not recognise the 'get protocol version' command"
-
-            verno = struct.unpack('<H', resp[2:])[0]
-            if verno < UsbConn._VER_MIN:
-                return "Version of device (%04x) too old, must be at least %04x" \
-                    % (hex(verno, USbConn._VER_MIN))
-            if verno > UsbConn._VER_MAX:
-                return "Version of device (%04x) too new, must be max. %04x" \
-                    % (hex(verno, USbConn._VER_MAX))
         except usb.core.USBError:
             return "Device is busy, already used by something else? (If you use "+\
                 "the kernel module, use a character device from /dev instead.)"
 
+        if len(resp) < 4 or resp[0] != 0 or resp[1] != 2:
+            return "Device does not recognise the 'get protocol version' command"
+
+        verno = struct.unpack('<H', resp[2:])[0]
+        if verno < DevConn._VER_MIN:
+            return "Version of device (%04x) too old, must be at least %04x" \
+                % (hex(verno, DevConn._VER_MIN))
+        if verno > DevConn._VER_MAX:
+            return "Version of device (%04x) too new, must be max. %04x" \
+                % (hex(verno, DevConn._VER_MAX))
+
         return UsbConn(dev, cfg, itf, epout, epin)
 
     def try_find() -> Optional[UsbConn]:
@@ -86,7 +89,8 @@ class UsbConn(DevConn):
         if dev is None or len(dev) != 1:
             return None
 
-        return UsbConn._open_dev(dev[0])
+        rv = UsbConn._open_dev(dev[0])
+        return None if isinstance(rv, str) else rv
 
     def is_usbdev_path(conn: str) -> bool:
         # eg. cafe:1312
@@ -175,17 +179,65 @@ class UsbConn(DevConn):
 
 
 class ChardevConn(DevConn):
+    _DEVCLASSNAME = "dmj"
+
     def try_find() -> Optional[ChardevConn]:
-        return None
+        if sys.platform != 'linux':
+            return None
+
+        opts = glob.glob("/dev/%s-*" % ChardevConn._DEVCLASSNAME)
+
+        if len(opts) != 1:
+            return None
+
+        rv = ChardevConn.try_open(opts[0])
+        return None if isinstance(rv, str) else rv
 
     def is_chardev_path(conn: str) -> bool:
-        return None
+        if sys.platform != 'linux':
+            return False
+
+        return re.match('^/dev/%s-[0-9]+$' % ChardevConn._DEVCLASSNAME, conn) is not None
 
     def try_open(conn: str) -> Union[ChardevConn, str]:
-        return "Could not open character device '%s'" % conn
+        if sys.platform != 'linux':
+            return "Chardev connections not available on %s, as these require "+\
+                "a Linux kernel module" % sys.platform
 
+        try:
+            fd = os.open(conn, os.O_RDWR)
+            if fd < 0:
+                raise OSError("Negative file descriptor returned")
+        except OSError as e:
+            return "Could not open character device '%s': %s" % \
+                (conn, e.message if hasattr(e, 'message') else e.strerror)
 
-    def __init__(self, fd):
+        os.write(fd, b'\x00')
+        resp = os.read(fd, 4)
+
+        if len(resp) < 4 or resp[0] != 0 or resp[1] != 2:
+            return "Device does not recognise the 'get protocol version' command"
+
+        verno = struct.unpack('<H', resp[2:])[0]
+        if verno < DevConn._VER_MIN:
+            return "Version of device (%04x) too old, must be at least %04x" \
+                % (hex(verno, DevConn._VER_MIN))
+        if verno > DevConn._VER_MAX:
+            return "Version of device (%04x) too new, must be max. %04x" \
+                % (hex(verno, DevConn._VER_MAX))
+
+        return ChardevConn(fd)
+
+    def read_raw(self, arr) -> int:
+        blob = os.read(self._fd, len(arr))
+        for i in range(len(blob)):  # TODO: memcpy?
+            arr[i] = blob[i]
+        return len(blob)
+
+    def write_raw(self, b: bytes) -> int:
+        return os.write(self._fd, b)
+
+    def __init__(self, fd: int):
         self._fd = fd
 
     def __enter__(self):