From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C36352E717B; Tue, 12 Aug 2025 08:46:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754988399; cv=none; b=j2OeL6E+rYoEP5gAoayG+u/XCE/0HaEVKsZHkOXXh56Grt/UcpPb9CRUikrPoqpO5gZrn1yxShbVR8H9XUbZSdeiXOSyUXw2Ew/daLClDp7ZaOAH3tnnpmh1b2h5QxTKSA6N8HZvSoZltUV88D59KILBSJWW21gvasWHyNLtcGo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754988399; c=relaxed/simple; bh=5vdh1riAR0ZL9xaLLQRBtVtO//nClfhfAq/IqeV6FBY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=mhvxgm1FO9fpiO7AKfG0X5TDKLe84/p/QiFYH6aI3p9uDHednN+dmoiA3tOPlP1yxnEVY++C7TPsZDEthQsDZsqlwA+Y4e5tUvmcvS8hurdB//zFuIynpApFYiFC4Xm90wOJpBdp34LEFqnc3pmPDbZDoUtwrQIilCynBq1xOF8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZPD/D0Z4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZPD/D0Z4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50E1BC4CEF0; Tue, 12 Aug 2025 08:46:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754988398; bh=5vdh1riAR0ZL9xaLLQRBtVtO//nClfhfAq/IqeV6FBY=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=ZPD/D0Z4UaD4iVP8yjxS4+6iYcJ392xZhUk6BdaEv35g1us/JnEDazC5fTkbogXrl tYKmB2FhB4fH1+n+zfwvHk9zB2WawE38DO9dCxbks3NfxMbEG+LB6+0kUJSxUNdOit aeopHDVSUNLSTOR03IOUAHT6f/xcOEIll3iOJ56Qj5Mz9r6WG0G0Mp0vZ/ZQVQnt5x EI6+kZmbkjg61xgf/onnEJyxRF22vTnzhMj7LuAfIFRbslv19xo9sty81J9sLVAmXx heXvN76DKe/KP48hKTHgNuem+L1+KcS+890S6x83pwblFH9tuVJ9GzKnp0LtXEjcKe Go3RvBr7k5sSg== From: Andreas Hindborg Date: Tue, 12 Aug 2025 10:44:22 +0200 Subject: [PATCH v4 04/15] rust: str: introduce `NullTerminatedFormatter` Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20250812-rnull-up-v6-16-v4-4-ed801dd3ba5c@kernel.org> References: <20250812-rnull-up-v6-16-v4-0-ed801dd3ba5c@kernel.org> In-Reply-To: <20250812-rnull-up-v6-16-v4-0-ed801dd3ba5c@kernel.org> To: Boqun Feng , Miguel Ojeda , Alex Gaynor , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Alice Ryhl , Trevor Gross , Danilo Krummrich , Jens Axboe Cc: linux-block@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Andreas Hindborg X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=2720; i=a.hindborg@kernel.org; h=from:subject:message-id; bh=5vdh1riAR0ZL9xaLLQRBtVtO//nClfhfAq/IqeV6FBY=; b=owEBbQKS/ZANAwAIAeG4Gj55KGN3AcsmYgBomv8fKlpJ8jBjQG7Hiw5jhqLFg/iPJu/OAJjPr lI8UDjotlaJAjMEAAEIAB0WIQQSwflHVr98KhXWwBLhuBo+eShjdwUCaJr/HwAKCRDhuBo+eShj dxdgD/kBvs3r8XCENbIp6EI7LHK7yDcd18oPIe4WjKcM17srqNA1W23fdXxzM6Ry0kpdjfD1R4v 3MPlNXPzD4ohFd2AM5ApFqhG8Ym28IH1UHRkJvdYYSnEN1jaV5yUzv+/AZC+BoV8GC9DyK9N+W2 CfBE/M33G4Rr8ZOQVwIu9fS5V7Aqq8M4L4DP4uappH90wGIvqAgQvmbdLW+LgsvWE4yxKuqwyxc E3iK+KFCo6lRUHcCKw64fG8yV3DwPPFk2mVI8WDKdky8sSkglJ8Nezk9ruTIXxi157oCuTwLt1N ejTAgTZIZz1dGp9Nxclb4JI3JFUKex/1BS/SWNEvAfLa1PnlIB4n+ukE8rL3WfcDm5DOt+2K+gi MCdhiMGzctEnC9p/LcIuz/9JaZyib8nIF0rH857tyMa9NZRPHtkAHCEmexTg3AY2WhnEv46s24Z sQiJ8hteUPu9xINr1BTe4MTEoDtcMiutlkGkiBxvv/wAxBTpQyintIIoLVz2NIQAa7QQEKPcCTO VqUz/kJGMlaqAhFA/MPerlK90N2UkGRGhFWEAu2MGhvr0Gf6vswAKDoKsLDkjrFncVpixFgFp0c p4qS5xFck4keRtbgMqV+VdGHtsjbvW6RMVt/F+LEvrfWZvlN8vMdjtq6udljN21VrDqsHg9qPnQ tBJqlRnf49ysphg== X-Developer-Key: i=a.hindborg@kernel.org; a=openpgp; fpr=3108C10F46872E248D1FB221376EB100563EF7A7 Add `NullTerminatedFormatter`, a formatter that writes a null terminated string to an array or slice buffer. Because this type needs to manage the trailing null marker, the existing formatters cannot be used to implement this type. Signed-off-by: Andreas Hindborg --- rust/kernel/str.rs | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs index 46cdc85dad63..e84f62c01815 100644 --- a/rust/kernel/str.rs +++ b/rust/kernel/str.rs @@ -871,6 +871,61 @@ fn write_str(&mut self, s: &str) -> fmt::Result { } } +/// A mutable reference to a byte buffer where a string can be written into. +/// +/// The buffer will be automatically null terminated after the last written character. +/// +/// # Invariants +/// +/// * The first byte of `buffer` is always zero. +/// * The length of `buffer` is at least 1. +pub(crate) struct NullTerminatedFormatter<'a> { + buffer: &'a mut [u8], +} + +impl<'a> NullTerminatedFormatter<'a> { + /// Create a new [`Self`] instance. + pub(crate) fn new(buffer: &'a mut [u8]) -> Option> { + *(buffer.first_mut()?) = 0; + + // INVARIANT: + // - We wrote zero to the first byte above. + // - If buffer was not at least length 1, `buffer.first_mut()` would return None. + Some(Self { buffer }) + } + + #[expect(dead_code)] + pub(crate) fn from_array( + buffer: &'a mut [crate::ffi::c_char; N], + ) -> Option> { + Self::new(buffer) + } +} + +impl Write for NullTerminatedFormatter<'_> { + fn write_str(&mut self, s: &str) -> fmt::Result { + let bytes = s.as_bytes(); + let len = bytes.len(); + + // We want space for a zero. By type invariant, buffer length is always at least 1, so no + // underflow. + if len > self.buffer.len() - 1 { + return Err(fmt::Error); + } + + let buffer = core::mem::take(&mut self.buffer); + // We break the zero start invariant for a short while. + buffer[..len].copy_from_slice(bytes); + // INVARIANT: We checked above that buffer will have size at least 1 after this assignment. + self.buffer = &mut buffer[len..]; + + // INVARIANT: We write zero to the first byte of the buffer. + self.buffer[0] = 0; + + Ok(()) + } +} + /// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end. /// /// Used for interoperability with kernel APIs that take C strings. -- 2.47.2