diff --git a/docs/source/conf.py b/docs/source/conf.py
index 5017f3895..46a3f6bae 100755
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -173,15 +173,6 @@ def autodoc_process_signature(
 # currently undocumented things
 logger = getLogger("trio")
 UNDOCUMENTED = {
-    "trio.MemorySendChannel",
-    "trio.MemoryReceiveChannel",
-    "trio.MemoryChannelStatistics",
-    "trio.SocketStream.aclose",
-    "trio.SocketStream.receive_some",
-    "trio.SocketStream.send_all",
-    "trio.SocketStream.send_eof",
-    "trio.SocketStream.wait_send_all_might_not_block",
-    "trio._subprocess.HasFileno.fileno",
     "trio.lowlevel.ParkingLot.broken_by",
 }
 
diff --git a/docs/source/reference-io.rst b/docs/source/reference-io.rst
index 665f62dd0..c9170f863 100644
--- a/docs/source/reference-io.rst
+++ b/docs/source/reference-io.rst
@@ -218,7 +218,6 @@ abstraction.
 
 .. autoclass:: SocketStream
    :members:
-   :undoc-members:
    :show-inheritance:
 
 .. autoclass:: SocketListener
diff --git a/newsfragments/3221.doc.rst b/newsfragments/3221.doc.rst
new file mode 100644
index 000000000..31c563cd0
--- /dev/null
+++ b/newsfragments/3221.doc.rst
@@ -0,0 +1 @@
+Added missing docstrings for public API classes and methods.
diff --git a/src/trio/_channel.py b/src/trio/_channel.py
index 05037d813..c2cdbfb7c 100644
--- a/src/trio/_channel.py
+++ b/src/trio/_channel.py
@@ -118,6 +118,12 @@ def __init__(self, max_buffer_size: int | float) -> None:  # noqa: PYI041
 
 @attrs.frozen
 class MemoryChannelStatistics:
+    """Statistics about a memory channel.
+
+    Returned by :meth:`MemorySendChannel.statistics` and
+    :meth:`MemoryReceiveChannel.statistics`.
+    """
+
     current_buffer_used: int
     max_buffer_size: int | float
     open_send_channels: int
@@ -152,6 +158,13 @@ def statistics(self) -> MemoryChannelStatistics:
 @final
 @attrs.define(eq=False, repr=False, slots=False)
 class MemorySendChannel(SendChannel[SendType], metaclass=NoPublicConstructor):
+    """The send end of a memory channel, created by
+    :func:`open_memory_channel`.
+
+    See :ref:`channels` for details.
+
+    """
+
     _state: MemoryChannelState[SendType]
     _closed: bool = False
     # This is just the tasks waiting on *this* object. As compared to
@@ -300,6 +313,13 @@ async def aclose(self) -> None:
 @final
 @attrs.define(eq=False, repr=False, slots=False)
 class MemoryReceiveChannel(ReceiveChannel[ReceiveType], metaclass=NoPublicConstructor):
+    """The receive end of a memory channel, created by
+    :func:`open_memory_channel`.
+
+    See :ref:`channels` for details.
+
+    """
+
     _state: MemoryChannelState[ReceiveType]
     _closed: bool = False
     _tasks: set[trio._core._run.Task] = attrs.Factory(set)
diff --git a/src/trio/_subprocess.py b/src/trio/_subprocess.py
index 145c2de9b..bff4008b5 100644
--- a/src/trio/_subprocess.py
+++ b/src/trio/_subprocess.py
@@ -98,7 +98,9 @@ def pidfd_open(fd: int, flags: int) -> int:
 class HasFileno(Protocol):
     """Represents any file-like object that has a file descriptor."""
 
-    def fileno(self) -> int: ...
+    def fileno(self) -> int:
+        """Return the underlying file descriptor as an integer."""
+        ...
 
 
 @final
diff --git a/src/trio/_tests/_check_type_completeness.json b/src/trio/_tests/_check_type_completeness.json
index 6e8c54ea8..c4f86a952 100644
--- a/src/trio/_tests/_check_type_completeness.json
+++ b/src/trio/_tests/_check_type_completeness.json
@@ -18,20 +18,8 @@
     ],
     "Windows": [],
     "all": [
-        "No docstring found for class \"trio.MemoryReceiveChannel\"",
-        "No docstring found for class \"trio._channel.MemoryReceiveChannel\"",
-        "No docstring found for class \"trio.MemoryChannelStatistics\"",
-        "No docstring found for class \"trio._channel.MemoryChannelStatistics\"",
-        "No docstring found for class \"trio.MemorySendChannel\"",
-        "No docstring found for class \"trio._channel.MemorySendChannel\"",
         "No docstring found for class \"trio._core._run.Task\"",
         "No docstring found for class \"trio._socket.SocketType\"",
-        "No docstring found for function \"trio._highlevel_socket.SocketStream.send_all\"",
-        "No docstring found for function \"trio._highlevel_socket.SocketStream.wait_send_all_might_not_block\"",
-        "No docstring found for function \"trio._highlevel_socket.SocketStream.send_eof\"",
-        "No docstring found for function \"trio._highlevel_socket.SocketStream.receive_some\"",
-        "No docstring found for function \"trio._highlevel_socket.SocketStream.aclose\"",
-        "No docstring found for function \"trio._subprocess.HasFileno.fileno\"",
         "No docstring found for class \"trio._sync.AsyncContextManagerMixin\"",
         "No docstring found for function \"trio._sync._HasAcquireRelease.acquire\"",
         "No docstring found for function \"trio._sync._HasAcquireRelease.release\"",