netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 76 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/remote-controller.rst b/Documentation/admin-guide/media/remote-controller.rst
new file mode 100644
index 000000000..188944b00
--- /dev/null
+++ b/Documentation/admin-guide/media/remote-controller.rst
@@ -0,0 +1,76 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================================
+Infrared remote control support in video4linux drivers
+======================================================
+
+Authors: Gerd Hoffmann, Mauro Carvalho Chehab
+
+Basics
+======
+
+Most analog and digital TV boards support remote controllers. Several of
+them have a microprocessor that receives the IR carriers, convert into
+pulse/space sequences and then to scan codes, returning such codes to
+userspace ("scancode mode"). Other boards return just the pulse/space
+sequences ("raw mode").
+
+The support for remote controller in scancode mode is provided by the
+standard Linux input layer. The support for raw mode is provided via LIRC.
+
+In order to check the support and test it, it is suggested to download
+the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_. It provides
+two tools to handle remote controllers:
+
+- ir-keytable: provides a way to query the remote controller, list the
+  protocols it supports, enable in-kernel support for IR decoder or
+  switch the protocol and to test the reception of scan codes;
+
+- ir-ctl: provide tools to handle remote controllers that support raw mode
+  via LIRC interface.
+
+Usually, the remote controller module is auto-loaded when the TV card is
+detected. However, for a few devices, you need to manually load the
+ir-kbd-i2c module.
+
+How it works
+============
+
+The modules register the remote as keyboard within the linux input
+layer, i.e. you'll see the keys of the remote as normal key strokes
+(if CONFIG_INPUT_KEYBOARD is enabled).
+
+Using the event devices (CONFIG_INPUT_EVDEV) it is possible for
+applications to access the remote via /dev/input/event<n> devices.
+The udev/systemd will automatically create the devices. If you install
+the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_, it may also
+automatically load a different keytable than the default one. Please see
+`v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ ir-keytable.1
+man page for details.
+
+The ir-keytable tool is nice for trouble shooting, i.e. to check
+whenever the input device is really present, which of the devices it
+is, check whenever pressing keys on the remote actually generates
+events and the like.  You can also use any other input utility that changes
+the keymaps, like the input kbd utility.
+
+
+Using with lircd
+----------------
+
+The latest versions of the lircd daemon supports reading events from the
+linux input layer (via event device). It also supports receiving IR codes
+in lirc mode.
+
+
+Using without lircd
+-------------------
+
+Xorg recognizes several IR keycodes that have its numerical value lower
+than 247. With the advent of Wayland, the input driver got updated too,
+and should now accept all keycodes. Yet, you may want to just reassign
+the keycodes to something that your favorite media application likes.
+
+This can be done by setting
+`v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ to load your own
+keytable in runtime. Please read  ir-keytable.1 man page for details.