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, 36 insertions, 0 deletions

diff --git a/drivers/accessibility/Kconfig b/drivers/accessibility/Kconfig
new file mode 100644
index 000000000..6b2f79d1f
--- /dev/null
+++ b/drivers/accessibility/Kconfig
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+menuconfig ACCESSIBILITY
+	bool "Accessibility support"
+	help
+	  Accessibility handles all special kinds of hardware devices or
+	  software adapters which help people with disabilities (e.g.
+	  blindness) to use computers.
+
+	  That includes braille devices, speech synthesis, keyboard
+	  remapping, etc.
+
+	  Say Y here to get to see options for accessibility.
+	  This option alone does not add any kernel code.
+
+	  If you say N, all options in this submenu will be skipped and disabled.
+
+	  If unsure, say N.
+
+if ACCESSIBILITY
+config A11Y_BRAILLE_CONSOLE
+	bool "Console on braille device"
+	depends on VT
+	depends on SERIAL_CORE_CONSOLE
+	help
+	  Enables console output on a braille device connected to a 8250
+	  serial port. For now only the VisioBraille device is supported.
+
+	  To actually enable it, you need to pass option
+	  console=brl,ttyS0
+	  to the kernel. Options are the same as for serial console.
+
+	  If unsure, say N.
+
+source "drivers/accessibility/speakup/Kconfig"
+
+endif # ACCESSIBILITY