linux-kernel - Re: [RFC PATCH 0/5] tty: Add KUnit test framework for TTY drivers

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Message-ID: <49070681-9111-404a-a965-ca2b2eb2988c@kernel.org>
Date: Sun, 31 Aug 2025 08:07:07 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Abhinav Saxena <xandfury@...il.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 Kees Cook <kees@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
 llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH 0/5] tty: Add KUnit test framework for TTY drivers

On 27. 08. 25, 0:51, Abhinav Saxena wrote:
> This patch series introduces a KUnit testing framework for the TTY
> subsystem, enabling deterministic, automated testing of TTY drivers and
> core functionality without requiring hardware or userspace interaction.
> 
> On an x86_64 build with CONFIG_GCOV enabled, these tests increased
> TTY subsystem coverage to approximately 10.6% line coverage and
> 14.7% function coverage [1].
> 
> Problem Statement
> -----------------
> Testing TTY drivers today requires:
> - User-space interaction through device nodes
> - Complex setup with ptys or real hardware
> - Limited ability to test error paths reliably and deterministically
> 
> This series solves these issues by providing in-kernel KUnit tests that
> exercise real TTY core paths under controlled, deterministic conditions.
> 
> What This Series Provides
> -------------------------
> 1. Reusable test helpers (`tty_test_helpers.h`):
>     - Minimal (~150 LOC) infrastructure that any TTY driver should be
>     able to use
>     - Automatic resource management
>     - Integrated into core files under KUnit guard, with
>       `EXPORT_SYMBOL_IF_KUNIT()` to keep the production symbol table
>       clean
> 
> 2. Mock TTY driver:
>     - Demonstrates how drivers can leverage the helpers
>     - Enables deterministic scenarios without hardware
> 
> 3. Core TTY tests:
>     - Validate open/close/read/write/termios paths
>     - Exercise hangup, resize, and error handling
>     - Ensure real kernel paths are tested, not mocked stubs
> 
> 4. ttynull driver tests:
>     - Validate data sink behavior of the null driver
>     - Provide a minimal driver contract baseline
> 
> 5. Optional coverage support:
>     - GCOV integration for test coverage analysis
> 
> Future Work
> -----------
> With this foundation merged, follow-up work can:
> - Add more coverage of TTY core functions
> - Enable each TTY driver to maintain its own KUnit suite
> - Introduce stress tests and race detection
> - Extend to include more tests for other tty drivers:
>    - UART drivers: test interrupt handling without hardware
>    - USB serial: validate disconnect and reconnect sequences
>    - PTY drivers: test resize, flow control, and hangups
>    - Virtual consoles: test Unicode and input handling
>    
> Testing
> -------
> - All patches pass `checkpatch.pl`
> - Verified on x86_64 with:
>      ./tools/testing/kunit/kunit.py run \
>          --kunitconfig=.kunit/ \
>          --kunitconfig=drivers/tty/tests/.kunitconfig \
>          --arch=x86_64
> - All tests pass (working around tty_read wrapper in progress)
> 
> Feedback welcome! :)

Wow, looks good. Has it found something yet :)?


FWIW
Reviewed-by: Jiri Slaby <jirislaby@...nel.org>

thanks,
-- 
js
suse labs