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, 26 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/c3-isp.dot b/Documentation/admin-guide/media/c3-isp.dot
new file mode 100644
index 000000000..42dc931ee
--- /dev/null
+++ b/Documentation/admin-guide/media/c3-isp.dot
@@ -0,0 +1,26 @@
+digraph board {
+	rankdir=TB
+	n00000001 [label="{{<port0> 0 | <port1> 1} | c3-isp-core\n/dev/v4l-subdev0 | {<port2> 2 | <port3> 3 | <port4> 4 | <port5> 5}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000001:port3 -> n00000008:port0
+	n00000001:port4 -> n0000000b:port0
+	n00000001:port5 -> n0000000e:port0
+	n00000001:port2 -> n00000027
+	n00000008 [label="{{<port0> 0} | c3-isp-resizer0\n/dev/v4l-subdev1 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000008:port1 -> n00000016 [style=bold]
+	n0000000b [label="{{<port0> 0} | c3-isp-resizer1\n/dev/v4l-subdev2 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000000b:port1 -> n0000001a [style=bold]
+	n0000000e [label="{{<port0> 0} | c3-isp-resizer2\n/dev/v4l-subdev3 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000000e:port1 -> n00000023 [style=bold]
+	n00000011 [label="{{<port0> 0} | c3-mipi-adapter\n/dev/v4l-subdev4 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000011:port1 -> n00000001:port0 [style=bold]
+	n00000016 [label="c3-isp-cap0\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+	n0000001a [label="c3-isp-cap1\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n0000001e [label="{{<port0> 0} | c3-mipi-csi2\n/dev/v4l-subdev5 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000001e:port1 -> n00000011:port0 [style=bold]
+	n00000023 [label="c3-isp-cap2\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+	n00000027 [label="c3-isp-stats\n/dev/video3", shape=box, style=filled, fillcolor=yellow]
+	n0000002b [label="c3-isp-params\n/dev/video4", shape=box, style=filled, fillcolor=yellow]
+	n0000002b -> n00000001:port1
+	n0000003f [label="{{} | imx290 2-001a\n/dev/v4l-subdev6 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000003f:port0 -> n0000001e:port0 [style=bold]
+}