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, 96 insertions, 0 deletions

diff --git a/Documentation/process/coding-assistants.rst b/Documentation/process/coding-assistants.rst
new file mode 100644
index 000000000..051f0d819
--- /dev/null
+++ b/Documentation/process/coding-assistants.rst
@@ -0,0 +1,96 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _coding_assistants:
+
+AI Coding Assistants
+++++++++++++++++++++
+
+This document provides guidance for AI tools and developers using AI
+assistance when contributing to the Linux kernel.
+
+AI tools helping with Linux kernel development should follow the standard
+kernel development process:
+
+* Documentation/process/development-process.rst
+* Documentation/process/coding-style.rst
+* Documentation/process/submitting-patches.rst
+
+For guidelines on content generated by AI coding assistants see:
+
+* Documentation/process/generated-content.rst
+
+Licensing and Legal Requirements
+================================
+
+All contributions must comply with the kernel's licensing requirements:
+
+* All code must be compatible with GPL-2.0-only
+* Use appropriate SPDX license identifiers
+* See Documentation/process/license-rules.rst for details
+
+Signed-off-by and Developer Certificate of Origin
+=================================================
+
+AI agents MUST NOT add Signed-off-by tags. Only humans can legally
+certify the Developer Certificate of Origin (DCO). The human submitter
+is responsible for:
+
+* Reviewing all AI-generated code
+* Ensuring compliance with licensing requirements
+* Adding their own Signed-off-by tag to certify the DCO
+* Taking full responsibility for the contribution
+
+Attribution
+===========
+
+When AI tools contribute to kernel development, proper attribution
+helps track the evolving role of AI in the development process.
+Contributions should include an Assisted-by tag in the following format::
+
+  Assisted-by: LLM [TOOL1] [TOOL2]
+
+* ``[TOOL1] [TOOL2]`` are optional specialized analysis tools used
+  (e.g., coccinelle, sparse, smatch, clang-tidy)
+
+Basic development tools (git, gcc, make, editors) should not be listed.
+
+Example::
+
+  Assisted-by: LLM coccinelle sparse
+
+Procedure for finding and fixing bugs
+=====================================
+
+When an AI assistant is used to find and fix bugs, it **MUST** follow at least
+these steps:
+
+1. Before starting, read the whole process documentation listed above, as well
+   as any other document mentioned in the request. Do not rely on isolated
+   parts found by keyword search.
+2. Note the commit ID and Locate a bug as instructed.
+3. For any bug found that is not trivial, verify that it looks real by
+   attempting to create a reproducer to demonstrate it. Lacking it may cause
+   the report to be ignored, as many unverified bug reports sent to maintainers
+   happen to be invalid. Stop here if it finally looks wrong.
+4. Write a fix for the bug. This part is not optional: except in a few very
+   rare cases, an AI assistant able to find a bug is able to fix it. Note that
+   fixes written in the same session as used to find the bug will generally
+   lead to better and more accurate fixes as the LLM's reasoning context
+   remains present.
+5. Build and verify that the fix works either using the reproducer or by
+   re-running a complete analysis; drop any fix that doesn't work and try
+   another one. The fix must not add build warnings and must pass the
+   checkpatch.pl checks (see submitting-patches.rst).
+6. Commit the working fix with a detailed message describing the problem, the
+   solution and a Fixes tag. Do not add a Signed-off-by tag, and add an
+   Assisted-by tag, as described above.
+7. Identify the maintainers and lists using scripts/get_maintainer.pl.
+   Documentation/process/security-bugs.rst shows how to do that.
+8. Indicate what could not be done. If the fix could not be built or tested, or
+   if no reproducer could be produced, say so explicitly: maintainers currently
+   waste too much time analyzing unverified reports and untested fixes.
+9. Read Documentation/process/threat-model.rst to determine whether the bug is
+   a vulnerability or a regular bug, and leave the result to the reporter for
+   review (the assistant must never send anything itself). Regular bugs are
+   submitted as described in Documentation/process/submitting-patches.rst,
+   vulnerabilities as described in Documentation/process/security-bugs.rst.