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, 27 insertions, 0 deletions

diff --git a/Documentation/admin-guide/lcd-panel-cgram.rst b/Documentation/admin-guide/lcd-panel-cgram.rst
new file mode 100644
index 000000000..a3eb00c62
--- /dev/null
+++ b/Documentation/admin-guide/lcd-panel-cgram.rst
@@ -0,0 +1,27 @@
+======================================
+Parallel port LCD/Keypad Panel support
+======================================
+
+Some LCDs allow you to define up to 8 characters, mapped to ASCII
+characters 0 to 7. The escape code to define a new character is
+'\e[LG' followed by one digit from 0 to 7, representing the character
+number, and up to 8 couples of hex digits terminated by a semi-colon
+(';'). Each couple of digits represents a line, with 1-bits for each
+illuminated pixel with LSB on the right. Lines are numbered from the
+top of the character to the bottom. On a 5x7 matrix, only the 5 lower
+bits of the 7 first bytes are used for each character. If the string
+is incomplete, only complete lines will be redefined. Here are some
+examples::
+
+  printf "\e[LG0010101050D1F0C04;"  => 0 = [enter]
+  printf "\e[LG1040E1F0000000000;"  => 1 = [up]
+  printf "\e[LG2000000001F0E0400;"  => 2 = [down]
+  printf "\e[LG3040E1F001F0E0400;"  => 3 = [up-down]
+  printf "\e[LG40002060E1E0E0602;"  => 4 = [left]
+  printf "\e[LG500080C0E0F0E0C08;"  => 5 = [right]
+  printf "\e[LG60016051516141400;"  => 6 = "IP"
+
+  printf "\e[LG00103071F1F070301;"  => big speaker
+  printf "\e[LG00002061E1E060200;"  => small speaker
+
+Willy