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, 55 insertions, 0 deletions

diff --git a/Documentation/gpu/meson.rst b/Documentation/gpu/meson.rst
new file mode 100644
index 000000000..b9e2f9aa3
--- /dev/null
+++ b/Documentation/gpu/meson.rst
@@ -0,0 +1,55 @@
+=============================================
+drm/meson AmLogic Meson Video Processing Unit
+=============================================
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_drv.c
+   :doc: Video Processing Unit
+
+Video Processing Unit
+=====================
+
+The Amlogic Meson Display controller is composed of several components
+that are going to be documented below:
+
+.. code::
+
+  DMC|---------------VPU (Video Processing Unit)----------------|------HHI------|
+     | vd1   _______     _____________    _________________     |               |
+  D  |-------|      |----|            |   |                |    |   HDMI PLL    |
+  D  | vd2   | VIU  |    | Video Post |   | Video Encoders |<---|-----VCLK      |
+  R  |-------|      |----| Processing |   |                |    |               |
+     | osd2  |      |    |            |---| Enci ----------|----|-----VDAC------|
+  R  |-------| CSC  |----| Scalers    |   | Encp ----------|----|----HDMI-TX----|
+  A  | osd1  |      |    | Blenders   |   | Encl ----------|----|---------------|
+  M  |-------|______|----|____________|   |________________|    |               |
+  ___|__________________________________________________________|_______________|
+
+Video Input Unit
+================
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_viu.c
+   :doc: Video Input Unit
+
+Video Post Processing
+=====================
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_vpp.c
+   :doc: Video Post Processing
+
+Video Encoder
+=============
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_venc.c
+   :doc: Video Encoder
+
+Video Clocks
+============
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_vclk.c
+   :doc: Video Clocks
+
+HDMI Video Output
+=================
+
+.. kernel-doc:: drivers/gpu/drm/meson/meson_dw_hdmi.c
+   :doc: HDMI Output