From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- Documentation/rust/coding-guidelines.rst | 216 +++++++++++++++++++++++++++++++ 1 file changed, 216 insertions(+) create mode 100644 Documentation/rust/coding-guidelines.rst (limited to 'Documentation/rust/coding-guidelines.rst') diff --git a/Documentation/rust/coding-guidelines.rst b/Documentation/rust/coding-guidelines.rst new file mode 100644 index 000000000..aa8ed0826 --- /dev/null +++ b/Documentation/rust/coding-guidelines.rst @@ -0,0 +1,216 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Coding Guidelines +================= + +This document describes how to write Rust code in the kernel. + + +Style & formatting +------------------ + +The code should be formatted using ``rustfmt``. In this way, a person +contributing from time to time to the kernel does not need to learn and +remember one more style guide. More importantly, reviewers and maintainers +do not need to spend time pointing out style issues anymore, and thus +less patch roundtrips may be needed to land a change. + +.. note:: Conventions on comments and documentation are not checked by + ``rustfmt``. Thus those are still needed to be taken care of. + +The default settings of ``rustfmt`` are used. This means the idiomatic Rust +style is followed. For instance, 4 spaces are used for indentation rather +than tabs. + +It is convenient to instruct editors/IDEs to format while typing, +when saving or at commit time. However, if for some reason reformatting +the entire kernel Rust sources is needed at some point, the following can be +run:: + + make LLVM=1 rustfmt + +It is also possible to check if everything is formatted (printing a diff +otherwise), for instance for a CI, with:: + + make LLVM=1 rustfmtcheck + +Like ``clang-format`` for the rest of the kernel, ``rustfmt`` works on +individual files, and does not require a kernel configuration. Sometimes it may +even work with broken code. + + +Comments +-------- + +"Normal" comments (i.e. ``//``, rather than code documentation which starts +with ``///`` or ``//!``) are written in Markdown the same way as documentation +comments are, even though they will not be rendered. This improves consistency, +simplifies the rules and allows to move content between the two kinds of +comments more easily. For instance: + +.. code-block:: rust + + // `object` is ready to be handled now. + f(object); + +Furthermore, just like documentation, comments are capitalized at the beginning +of a sentence and ended with a period (even if it is a single sentence). This +includes ``// SAFETY:``, ``// TODO:`` and other "tagged" comments, e.g.: + +.. code-block:: rust + + // FIXME: The error should be handled properly. + +Comments should not be used for documentation purposes: comments are intended +for implementation details, not users. This distinction is useful even if the +reader of the source file is both an implementor and a user of an API. In fact, +sometimes it is useful to use both comments and documentation at the same time. +For instance, for a ``TODO`` list or to comment on the documentation itself. +For the latter case, comments can be inserted in the middle; that is, closer to +the line of documentation to be commented. For any other case, comments are +written after the documentation, e.g.: + +.. code-block:: rust + + /// Returns a new [`Foo`]. + /// + /// # Examples + /// + // TODO: Find a better example. + /// ``` + /// let foo = f(42); + /// ``` + // FIXME: Use fallible approach. + pub fn f(x: i32) -> Foo { + // ... + } + +One special kind of comments are the ``// SAFETY:`` comments. These must appear +before every ``unsafe`` block, and they explain why the code inside the block is +correct/sound, i.e. why it cannot trigger undefined behavior in any case, e.g.: + +.. code-block:: rust + + // SAFETY: `p` is valid by the safety requirements. + unsafe { *p = 0; } + +``// SAFETY:`` comments are not to be confused with the ``# Safety`` sections +in code documentation. ``# Safety`` sections specify the contract that callers +(for functions) or implementors (for traits) need to abide by. ``// SAFETY:`` +comments show why a call (for functions) or implementation (for traits) actually +respects the preconditions stated in a ``# Safety`` section or the language +reference. + + +Code documentation +------------------ + +Rust kernel code is not documented like C kernel code (i.e. via kernel-doc). +Instead, the usual system for documenting Rust code is used: the ``rustdoc`` +tool, which uses Markdown (a lightweight markup language). + +To learn Markdown, there are many guides available out there. For instance, +the one at: + + https://commonmark.org/help/ + +This is how a well-documented Rust function may look like: + +.. code-block:: rust + + /// Returns the contained [`Some`] value, consuming the `self` value, + /// without checking that the value is not [`None`]. + /// + /// # Safety + /// + /// Calling this method on [`None`] is *[undefined behavior]*. + /// + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// let x = Some("air"); + /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); + /// ``` + pub unsafe fn unwrap_unchecked(self) -> T { + match self { + Some(val) => val, + + // SAFETY: The safety contract must be upheld by the caller. + None => unsafe { hint::unreachable_unchecked() }, + } + } + +This example showcases a few ``rustdoc`` features and some conventions followed +in the kernel: + + - The first paragraph must be a single sentence briefly describing what + the documented item does. Further explanations must go in extra paragraphs. + + - Unsafe functions must document their safety preconditions under + a ``# Safety`` section. + + - While not shown here, if a function may panic, the conditions under which + that happens must be described under a ``# Panics`` section. + + Please note that panicking should be very rare and used only with a good + reason. In almost all cases, a fallible approach should be used, typically + returning a ``Result``. + + - If providing examples of usage would help readers, they must be written in + a section called ``# Examples``. + + - Rust items (functions, types, constants...) must be linked appropriately + (``rustdoc`` will create a link automatically). + + - Any ``unsafe`` block must be preceded by a ``// SAFETY:`` comment + describing why the code inside is sound. + + While sometimes the reason might look trivial and therefore unneeded, + writing these comments is not just a good way of documenting what has been + taken into account, but most importantly, it provides a way to know that + there are no *extra* implicit constraints. + +To learn more about how to write documentation for Rust and extra features, +please take a look at the ``rustdoc`` book at: + + https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html + + +Naming +------ + +Rust kernel code follows the usual Rust naming conventions: + + https://rust-lang.github.io/api-guidelines/naming.html + +When existing C concepts (e.g. macros, functions, objects...) are wrapped into +a Rust abstraction, a name as close as reasonably possible to the C side should +be used in order to avoid confusion and to improve readability when switching +back and forth between the C and Rust sides. For instance, macros such as +``pr_info`` from C are named the same in the Rust side. + +Having said that, casing should be adjusted to follow the Rust naming +conventions, and namespacing introduced by modules and types should not be +repeated in the item names. For instance, when wrapping constants like: + +.. code-block:: c + + #define GPIO_LINE_DIRECTION_IN 0 + #define GPIO_LINE_DIRECTION_OUT 1 + +The equivalent in Rust may look like (ignoring documentation): + +.. code-block:: rust + + pub mod gpio { + pub enum LineDirection { + In = bindings::GPIO_LINE_DIRECTION_IN as _, + Out = bindings::GPIO_LINE_DIRECTION_OUT as _, + } + } + +That is, the equivalent of ``GPIO_LINE_DIRECTION_IN`` would be referred to as +``gpio::LineDirection::In``. In particular, it should not be named +``gpio::gpio_line_direction::GPIO_LINE_DIRECTION_IN``. -- cgit v1.2.3