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, 45 insertions, 0 deletions

diff --git a/Documentation/driver-api/tty/console.rst b/Documentation/driver-api/tty/console.rst
new file mode 100644
index 000000000..4348e36cd
--- /dev/null
+++ b/Documentation/driver-api/tty/console.rst
@@ -0,0 +1,45 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======
+Console
+=======
+
+.. contents:: :local:
+
+Struct Console
+==============
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: console cons_flags
+
+Internals
+---------
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: nbcon_state nbcon_prio nbcon_context nbcon_write_context
+
+Struct Consw
+============
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: consw
+
+Console functions
+=================
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: console_srcu_read_flags console_srcu_write_flags
+        console_is_registered for_each_console_srcu for_each_console
+
+.. kernel-doc:: drivers/tty/vt/selection.c
+   :export:
+.. kernel-doc:: drivers/tty/vt/vt.c
+   :export:
+
+Internals
+---------
+
+.. kernel-doc:: drivers/tty/vt/selection.c
+   :internal:
+.. kernel-doc:: drivers/tty/vt/vt.c
+   :internal: