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, 69 insertions, 0 deletions

diff --git a/Documentation/gpu/nova/guidelines.rst b/Documentation/gpu/nova/guidelines.rst
new file mode 100644
index 000000000..13ab13984
--- /dev/null
+++ b/Documentation/gpu/nova/guidelines.rst
@@ -0,0 +1,69 @@
+.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+
+==========
+Guidelines
+==========
+
+This document describes the general project guidelines that apply to nova-core
+and nova-drm.
+
+Language
+========
+
+The Nova project uses the Rust programming language. In this context, all rules
+of the Rust for Linux project as documented in
+:doc:`../../rust/general-information` apply. Additionally, the following rules
+apply.
+
+- Unless technically necessary otherwise (e.g. uAPI), any driver code is written
+  in Rust.
+
+- Unless technically necessary, unsafe Rust code must be avoided. In case of
+  technical necessity, unsafe code should be isolated in a separate component
+  providing a safe API for other driver code to use.
+
+Style
+-----
+
+All rules of the Rust for Linux project as documented in
+:doc:`../../rust/coding-guidelines` apply.
+
+For a submit checklist, please also see the `Rust for Linux Submit checklist
+addendum <https://rust-for-linux.com/contributing#submit-checklist-addendum>`_.
+
+Documentation
+=============
+
+The availability of proper documentation is essential in terms of scalability,
+accessibility for new contributors and maintainability of a project in general,
+but especially for a driver running as complex hardware as Nova is targeting.
+
+Hence, adding documentation of any kind is very much encouraged by the project.
+
+Besides that, there are some minimum requirements.
+
+- Every non-private structure needs at least a brief doc comment explaining the
+  semantical sense of the structure, as well as potential locking and lifetime
+  requirements. It is encouraged to have the same minimum documentation for
+  non-trivial private structures.
+
+- uAPIs must be fully documented with kernel-doc comments; additionally, the
+  semantical behavior must be explained including potential special or corner
+  cases.
+
+- The APIs connecting the 1st level driver (nova-core) with 2nd level drivers
+  must be fully documented. This includes doc comments, potential locking and
+  lifetime requirements, as well as example code if applicable.
+
+- Abbreviations must be explained when introduced; terminology must be uniquely
+  defined.
+
+- Register addresses, layouts, shift values and masks must be defined properly;
+  unless obvious, the semantical sense must be documented. This only applies if
+  the author is able to obtain the corresponding information.
+
+Acceptance Criteria
+===================
+
+- Patches must only be applied if reviewed by at least one other person on the
+  mailing list; this also applies for maintainers.