inotify: Correctly handle multi-struct reads

When reading from the *inotify* file descriptor, multiple structs can be
returned. Because the read loop was incorrectly calculating offsets,
messages would frequently get lost in this way. This commit simplifies
the logic of the read loop, using only a single position indicator and
correctly calculating all offsets from that on each iteration. The
result is that no more messages are incorrectly skipped.

src/linuxapi/inotify.py

@@ -119,9 +119,9 @@ class InotifyError(OSError):
 class Inotify(object):
     '''Wrapper class for Linux inotify capabilities'''
 
-    BUFSIZE = 4096
     STRUCT_FMT = '@iIII'
     STRUCT_SIZE = struct.calcsize(STRUCT_FMT)
+    BUFSIZE = STRUCT_SIZE + 256
 
     def __init__(self):
         fd = _libc.inotify_init()
@@ -173,21 +173,19 @@ class Inotify(object):
 
         buf = memoryview(os.read(self.__fd, self.BUFSIZE))
         nread = len(buf)
-        i = begin = 0
-        end = self.STRUCT_SIZE
-        while i < nread:
-            wd, mask, cookie, sz = self._unpack(buf[begin:end])
-            begin = end
-            end += sz
-            x = begin
-            while buf[x:x + 1] != b'\x00':
-                x += 1
-            name = buf[begin:x].tobytes()
+        pos = 0
+        while pos < nread:
+            packed = buf[pos:pos + self.STRUCT_SIZE]
+            pos += self.STRUCT_SIZE
+            wd, mask, cookie, sz = self._unpack(packed)
+            if sz:
+                name = buf[pos:pos + sz].tobytes()
+                name = name[:name.index(b'\x00')]
+                pos += sz
+            else:
+                name = None
             pathname = self.__watches[wd]
-            i += end
             yield Event(wd, mask, cookie, name, pathname)
-            begin = end
-            end += self.STRUCT_SIZE
 
     def close(self):
         '''Close all watch descriptors and the inotify descriptor'''