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/process/3.Early-stage.rst | 223 ++++++++++++++++++++++++++++++++ 1 file changed, 223 insertions(+) create mode 100644 Documentation/process/3.Early-stage.rst (limited to 'Documentation/process/3.Early-stage.rst') diff --git a/Documentation/process/3.Early-stage.rst b/Documentation/process/3.Early-stage.rst new file mode 100644 index 000000000..894a92004 --- /dev/null +++ b/Documentation/process/3.Early-stage.rst @@ -0,0 +1,223 @@ +.. _development_early_stage: + +Early-stage planning +==================== + +When contemplating a Linux kernel development project, it can be tempting +to jump right in and start coding. As with any significant project, +though, much of the groundwork for success is best laid before the first +line of code is written. Some time spent in early planning and +communication can save far more time later on. + + +Specifying the problem +---------------------- + +Like any engineering project, a successful kernel enhancement starts with a +clear description of the problem to be solved. In some cases, this step is +easy: when a driver is needed for a specific piece of hardware, for +example. In others, though, it is tempting to confuse the real problem +with the proposed solution, and that can lead to difficulties. + +Consider an example: some years ago, developers working with Linux audio +sought a way to run applications without dropouts or other artifacts caused +by excessive latency in the system. The solution they arrived at was a +kernel module intended to hook into the Linux Security Module (LSM) +framework; this module could be configured to give specific applications +access to the realtime scheduler. This module was implemented and sent to +the linux-kernel mailing list, where it immediately ran into problems. + +To the audio developers, this security module was sufficient to solve their +immediate problem. To the wider kernel community, though, it was seen as a +misuse of the LSM framework (which is not intended to confer privileges +onto processes which they would not otherwise have) and a risk to system +stability. Their preferred solutions involved realtime scheduling access +via the rlimit mechanism for the short term, and ongoing latency reduction +work in the long term. + +The audio community, however, could not see past the particular solution +they had implemented; they were unwilling to accept alternatives. The +resulting disagreement left those developers feeling disillusioned with the +entire kernel development process; one of them went back to an audio list +and posted this: + + There are a number of very good Linux kernel developers, but they + tend to get outshouted by a large crowd of arrogant fools. Trying + to communicate user requirements to these people is a waste of + time. They are much too "intelligent" to listen to lesser mortals. + +(https://lwn.net/Articles/131776/). + +The reality of the situation was different; the kernel developers were far +more concerned about system stability, long-term maintenance, and finding +the right solution to the problem than they were with a specific module. +The moral of the story is to focus on the problem - not a specific solution +- and to discuss it with the development community before investing in the +creation of a body of code. + +So, when contemplating a kernel development project, one should obtain +answers to a short set of questions: + + - What, exactly, is the problem which needs to be solved? + + - Who are the users affected by this problem? Which use cases should the + solution address? + + - How does the kernel fall short in addressing that problem now? + +Only then does it make sense to start considering possible solutions. + + +Early discussion +---------------- + +When planning a kernel development project, it makes great sense to hold +discussions with the community before launching into implementation. Early +communication can save time and trouble in a number of ways: + + - It may well be that the problem is addressed by the kernel in ways which + you have not understood. The Linux kernel is large and has a number of + features and capabilities which are not immediately obvious. Not all + kernel capabilities are documented as well as one might like, and it is + easy to miss things. Your author has seen the posting of a complete + driver which duplicated an existing driver that the new author had been + unaware of. Code which reinvents existing wheels is not only wasteful; + it will also not be accepted into the mainline kernel. + + - There may be elements of the proposed solution which will not be + acceptable for mainline merging. It is better to find out about + problems like this before writing the code. + + - It's entirely possible that other developers have thought about the + problem; they may have ideas for a better solution, and may be willing + to help in the creation of that solution. + +Years of experience with the kernel development community have taught a +clear lesson: kernel code which is designed and developed behind closed +doors invariably has problems which are only revealed when the code is +released into the community. Sometimes these problems are severe, +requiring months or years of effort before the code can be brought up to +the kernel community's standards. Some examples include: + + - The Devicescape network stack was designed and implemented for + single-processor systems. It could not be merged into the mainline + until it was made suitable for multiprocessor systems. Retrofitting + locking and such into code is a difficult task; as a result, the merging + of this code (now called mac80211) was delayed for over a year. + + - The Reiser4 filesystem included a number of capabilities which, in the + core kernel developers' opinion, should have been implemented in the + virtual filesystem layer instead. It also included features which could + not easily be implemented without exposing the system to user-caused + deadlocks. The late revelation of these problems - and refusal to + address some of them - has caused Reiser4 to stay out of the mainline + kernel. + + - The AppArmor security module made use of internal virtual filesystem + data structures in ways which were considered to be unsafe and + unreliable. This concern (among others) kept AppArmor out of the + mainline for years. + +In each of these cases, a great deal of pain and extra work could have been +avoided with some early discussion with the kernel developers. + + +Who do you talk to? +------------------- + +When developers decide to take their plans public, the next question will +be: where do we start? The answer is to find the right mailing list(s) and +the right maintainer. For mailing lists, the best approach is to look in +the MAINTAINERS file for a relevant place to post. If there is a suitable +subsystem list, posting there is often preferable to posting on +linux-kernel; you are more likely to reach developers with expertise in the +relevant subsystem and the environment may be more supportive. + +Finding maintainers can be a bit harder. Again, the MAINTAINERS file is +the place to start. That file tends to not always be up to date, though, +and not all subsystems are represented there. The person listed in the +MAINTAINERS file may, in fact, not be the person who is actually acting in +that role currently. So, when there is doubt about who to contact, a +useful trick is to use git (and "git log" in particular) to see who is +currently active within the subsystem of interest. Look at who is writing +patches, and who, if anybody, is attaching Signed-off-by lines to those +patches. Those are the people who will be best placed to help with a new +development project. + +The task of finding the right maintainer is sometimes challenging enough +that the kernel developers have added a script to ease the process: + +:: + + .../scripts/get_maintainer.pl + +This script will return the current maintainer(s) for a given file or +directory when given the "-f" option. If passed a patch on the +command line, it will list the maintainers who should probably receive +copies of the patch. This is the preferred way (unlike "-f" option) to get the +list of people to Cc for your patches. There are a number of options +regulating how hard get_maintainer.pl will search for maintainers; please be +careful about using the more aggressive options as you may end up including +developers who have no real interest in the code you are modifying. + +If all else fails, talking to Andrew Morton can be an effective way to +track down a maintainer for a specific piece of code. + + +When to post? +------------- + +If possible, posting your plans during the early stages can only be +helpful. Describe the problem being solved and any plans that have been +made on how the implementation will be done. Any information you can +provide can help the development community provide useful input on the +project. + +One discouraging thing which can happen at this stage is not a hostile +reaction, but, instead, little or no reaction at all. The sad truth of the +matter is (1) kernel developers tend to be busy, (2) there is no shortage +of people with grand plans and little code (or even prospect of code) to +back them up, and (3) nobody is obligated to review or comment on ideas +posted by others. Beyond that, high-level designs often hide problems +which are only revealed when somebody actually tries to implement those +designs; for that reason, kernel developers would rather see the code. + +If a request-for-comments posting yields little in the way of comments, do +not assume that it means there is no interest in the project. +Unfortunately, you also cannot assume that there are no problems with your +idea. The best thing to do in this situation is to proceed, keeping the +community informed as you go. + + +Getting official buy-in +----------------------- + +If your work is being done in a corporate environment - as most Linux +kernel work is - you must, obviously, have permission from suitably +empowered managers before you can post your company's plans or code to a +public mailing list. The posting of code which has not been cleared for +release under a GPL-compatible license can be especially problematic; the +sooner that a company's management and legal staff can agree on the posting +of a kernel development project, the better off everybody involved will be. + +Some readers may be thinking at this point that their kernel work is +intended to support a product which does not yet have an officially +acknowledged existence. Revealing their employer's plans on a public +mailing list may not be a viable option. In cases like this, it is worth +considering whether the secrecy is really necessary; there is often no real +need to keep development plans behind closed doors. + +That said, there are also cases where a company legitimately cannot +disclose its plans early in the development process. Companies with +experienced kernel developers may choose to proceed in an open-loop manner +on the assumption that they will be able to avoid serious integration +problems later. For companies without that sort of in-house expertise, the +best option is often to hire an outside developer to review the plans under +a non-disclosure agreement. The Linux Foundation operates an NDA program +designed to help with this sort of situation; more information can be found +at: + + https://www.linuxfoundation.org/nda/ + +This kind of review is often enough to avoid serious problems later on +without requiring public disclosure of the project. -- cgit v1.2.3