extmod/vfs_reader: Add file ioctl to set read buffer size.

Can be used to speed up importing a file from a vfs based filesystem.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

tests/extmod/vfs_userfs.py

@@ -16,6 +16,8 @@ except (ImportError, AttributeError):
 
 
 class UserFile(io.IOBase):
+    buffer_size = 16
+
     def __init__(self, mode, data):
         assert isinstance(data, bytes)
         self.is_text = mode.find("b") == -1
@@ -39,7 +41,11 @@ class UserFile(io.IOBase):
 
     def ioctl(self, req, arg):
         print("ioctl", req, arg)
-        return 0
+        if req == 4:  # MP_STREAM_CLOSE
+            return 0
+        if req == 11:  # MP_STREAM_GET_BUFFER_SIZE
+            return UserFile.buffer_size
+        return -1
 
 
 class UserFS:
@@ -70,6 +76,8 @@ user_files = {
     "/usermod2.py": b"print('in usermod2')",
     "/usermod3.py": b"syntax error",
     "/usermod4.mpy": b"syntax error",
+    "/usermod5.py": b"print('in usermod5')",
+    "/usermod6.py": b"print('in usermod6')",
 }
 os.mount(UserFS(user_files), "/userfs")
 
@@ -93,6 +101,14 @@ try:
 except ValueError:
     print("ValueError in usermod4")
 
+# Test an import with largest buffer size
+UserFile.buffer_size = 255
+import usermod5
+
+# Test an import with over-size buffer size (should be safely limited internally)
+UserFile.buffer_size = 1024
+import usermod6
+
 # unmount and undo path addition
 os.umount("/userfs")
 sys.path.pop()

tests/extmod/vfs_userfs.py.exp

@@ -3,21 +3,37 @@ some data in a text file
 stat /usermod1
 stat /usermod1.py
 open /usermod1.py rb
+ioctl 11 0
 ioctl 4 0
 in usermod1
 stat /usermod2
 stat /usermod2.py
 open /usermod2.py rb
+ioctl 11 0
 ioctl 4 0
 in usermod2
 stat /usermod3
 stat /usermod3.py
 open /usermod3.py rb
+ioctl 11 0
 ioctl 4 0
 SyntaxError in usermod3
 stat /usermod4
 stat /usermod4.py
 stat /usermod4.mpy
 open /usermod4.mpy rb
+ioctl 11 0
 ioctl 4 0
 ValueError in usermod4
+stat /usermod5
+stat /usermod5.py
+open /usermod5.py rb
+ioctl 11 0
+ioctl 4 0
+in usermod5
+stat /usermod6
+stat /usermod6.py
+open /usermod6.py rb
+ioctl 11 0
+ioctl 4 0
+in usermod6