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/7.AdvancedTopics.rst | 178 +++++++++++++++++++++++++++++ 1 file changed, 178 insertions(+) create mode 100644 Documentation/process/7.AdvancedTopics.rst (limited to 'Documentation/process/7.AdvancedTopics.rst') diff --git a/Documentation/process/7.AdvancedTopics.rst b/Documentation/process/7.AdvancedTopics.rst new file mode 100644 index 000000000..bf7cbfb4c --- /dev/null +++ b/Documentation/process/7.AdvancedTopics.rst @@ -0,0 +1,178 @@ +.. _development_advancedtopics: + +Advanced topics +=============== + +At this point, hopefully, you have a handle on how the development process +works. There is still more to learn, however! This section will cover a +number of topics which can be helpful for developers wanting to become a +regular part of the Linux kernel development process. + +Managing patches with git +------------------------- + +The use of distributed version control for the kernel began in early 2002, +when Linus first started playing with the proprietary BitKeeper +application. While BitKeeper was controversial, the approach to software +version management it embodied most certainly was not. Distributed version +control enabled an immediate acceleration of the kernel development +project. In current times, there are several free alternatives to +BitKeeper. For better or for worse, the kernel project has settled on git +as its tool of choice. + +Managing patches with git can make life much easier for the developer, +especially as the volume of those patches grows. Git also has its rough +edges and poses certain hazards; it is a young and powerful tool which is +still being civilized by its developers. This document will not attempt to +teach the reader how to use git; that would be sufficient material for a +long document in its own right. Instead, the focus here will be on how git +fits into the kernel development process in particular. Developers who +wish to come up to speed with git will find more information at: + + https://git-scm.com/ + + https://www.kernel.org/pub/software/scm/git/docs/user-manual.html + +and on various tutorials found on the web. + +The first order of business is to read the above sites and get a solid +understanding of how git works before trying to use it to make patches +available to others. A git-using developer should be able to obtain a copy +of the mainline repository, explore the revision history, commit changes to +the tree, use branches, etc. An understanding of git's tools for the +rewriting of history (such as rebase) is also useful. Git comes with its +own terminology and concepts; a new user of git should know about refs, +remote branches, the index, fast-forward merges, pushes and pulls, detached +heads, etc. It can all be a little intimidating at the outset, but the +concepts are not that hard to grasp with a bit of study. + +Using git to generate patches for submission by email can be a good +exercise while coming up to speed. + +When you are ready to start putting up git trees for others to look at, you +will, of course, need a server that can be pulled from. Setting up such a +server with git-daemon is relatively straightforward if you have a system +which is accessible to the Internet. Otherwise, free, public hosting sites +(Github, for example) are starting to appear on the net. Established +developers can get an account on kernel.org, but those are not easy to come +by; see https://kernel.org/faq/ for more information. + +The normal git workflow involves the use of a lot of branches. Each line +of development can be separated into a separate "topic branch" and +maintained independently. Branches in git are cheap, there is no reason to +not make free use of them. And, in any case, you should not do your +development in any branch which you intend to ask others to pull from. +Publicly-available branches should be created with care; merge in patches +from development branches when they are in complete form and ready to go - +not before. + +Git provides some powerful tools which can allow you to rewrite your +development history. An inconvenient patch (one which breaks bisection, +say, or which has some other sort of obvious bug) can be fixed in place or +made to disappear from the history entirely. A patch series can be +rewritten as if it had been written on top of today's mainline, even though +you have been working on it for months. Changes can be transparently +shifted from one branch to another. And so on. Judicious use of git's +ability to revise history can help in the creation of clean patch sets with +fewer problems. + +Excessive use of this capability can lead to other problems, though, beyond +a simple obsession for the creation of the perfect project history. +Rewriting history will rewrite the changes contained in that history, +turning a tested (hopefully) kernel tree into an untested one. But, beyond +that, developers cannot easily collaborate if they do not have a shared +view of the project history; if you rewrite history which other developers +have pulled into their repositories, you will make life much more difficult +for those developers. So a simple rule of thumb applies here: history +which has been exported to others should generally be seen as immutable +thereafter. + +So, once you push a set of changes to your publicly-available server, those +changes should not be rewritten. Git will attempt to enforce this rule if +you try to push changes which do not result in a fast-forward merge +(i.e. changes which do not share the same history). It is possible to +override this check, and there may be times when it is necessary to rewrite +an exported tree. Moving changesets between trees to avoid conflicts in +linux-next is one example. But such actions should be rare. This is one +of the reasons why development should be done in private branches (which +can be rewritten if necessary) and only moved into public branches when +it's in a reasonably advanced state. + +As the mainline (or other tree upon which a set of changes is based) +advances, it is tempting to merge with that tree to stay on the leading +edge. For a private branch, rebasing can be an easy way to keep up with +another tree, but rebasing is not an option once a tree is exported to the +world. Once that happens, a full merge must be done. Merging occasionally +makes good sense, but overly frequent merges can clutter the history +needlessly. Suggested technique in this case is to merge infrequently, and +generally only at specific release points (such as a mainline -rc +release). If you are nervous about specific changes, you can always +perform test merges in a private branch. The git "rerere" tool can be +useful in such situations; it remembers how merge conflicts were resolved +so that you don't have to do the same work twice. + +One of the biggest recurring complaints about tools like git is this: the +mass movement of patches from one repository to another makes it easy to +slip in ill-advised changes which go into the mainline below the review +radar. Kernel developers tend to get unhappy when they see that kind of +thing happening; putting up a git tree with unreviewed or off-topic patches +can affect your ability to get trees pulled in the future. Quoting Linus: + +:: + + You can send me patches, but for me to pull a git patch from you, I + need to know that you know what you're doing, and I need to be able + to trust things *without* then having to go and check every + individual change by hand. + +(https://lwn.net/Articles/224135/). + +To avoid this kind of situation, ensure that all patches within a given +branch stick closely to the associated topic; a "driver fixes" branch +should not be making changes to the core memory management code. And, most +importantly, do not use a git tree to bypass the review process. Post an +occasional summary of the tree to the relevant list, and, when the time is +right, request that the tree be included in linux-next. + +If and when others start to send patches for inclusion into your tree, +don't forget to review them. Also ensure that you maintain the correct +authorship information; the git "am" tool does its best in this regard, but +you may have to add a "From:" line to the patch if it has been relayed to +you via a third party. + +When requesting a pull, be sure to give all the relevant information: where +your tree is, what branch to pull, and what changes will result from the +pull. The git request-pull command can be helpful in this regard; it will +format the request as other developers expect, and will also check to be +sure that you have remembered to push those changes to the public server. + + +Reviewing patches +----------------- + +Some readers will certainly object to putting this section with "advanced +topics" on the grounds that even beginning kernel developers should be +reviewing patches. It is certainly true that there is no better way to +learn how to program in the kernel environment than by looking at code +posted by others. In addition, reviewers are forever in short supply; by +looking at code you can make a significant contribution to the process as a +whole. + +Reviewing code can be an intimidating prospect, especially for a new kernel +developer who may well feel nervous about questioning code - in public - +which has been posted by those with more experience. Even code written by +the most experienced developers can be improved, though. Perhaps the best +piece of advice for reviewers (all reviewers) is this: phrase review +comments as questions rather than criticisms. Asking "how does the lock +get released in this path?" will always work better than stating "the +locking here is wrong." + +Different developers will review code from different points of view. Some +are mostly concerned with coding style and whether code lines have trailing +white space. Others will focus primarily on whether the change implemented +by the patch as a whole is a good thing for the kernel or not. Yet others +will check for problematic locking, excessive stack usage, possible +security issues, duplication of code found elsewhere, adequate +documentation, adverse effects on performance, user-space ABI changes, etc. +All types of review, if they lead to better code going into the kernel, are +welcome and worthwhile. -- cgit v1.2.3