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authorLinus Torvalds <torvalds@linux-foundation.org>2022-12-14 02:47:48 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-12-14 02:47:48 +0300
commit7e68dd7d07a28faa2e6574dd6b9dbd90cdeaae91 (patch)
treeae0427c5a3b905f24b3a44b510a9bcf35d9b67a3 /Documentation/bpf/map_array.rst
parent1ca06f1c1acecbe02124f14a37cce347b8c1a90c (diff)
parent7c4a6309e27f411743817fe74a832ec2d2798a4b (diff)
downloadlinux-7e68dd7d07a28faa2e6574dd6b9dbd90cdeaae91.tar.xz
Merge tag 'net-next-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next
Pull networking updates from Paolo Abeni: "Core: - Allow live renaming when an interface is up - Add retpoline wrappers for tc, improving considerably the performances of complex queue discipline configurations - Add inet drop monitor support - A few GRO performance improvements - Add infrastructure for atomic dev stats, addressing long standing data races - De-duplicate common code between OVS and conntrack offloading infrastructure - A bunch of UBSAN_BOUNDS/FORTIFY_SOURCE improvements - Netfilter: introduce packet parser for tunneled packets - Replace IPVS timer-based estimators with kthreads to scale up the workload with the number of available CPUs - Add the helper support for connection-tracking OVS offload BPF: - Support for user defined BPF objects: the use case is to allocate own objects, build own object hierarchies and use the building blocks to build own data structures flexibly, for example, linked lists in BPF - Make cgroup local storage available to non-cgroup attached BPF programs - Avoid unnecessary deadlock detection and failures wrt BPF task storage helpers - A relevant bunch of BPF verifier fixes and improvements - Veristat tool improvements to support custom filtering, sorting, and replay of results - Add LLVM disassembler as default library for dumping JITed code - Lots of new BPF documentation for various BPF maps - Add bpf_rcu_read_{,un}lock() support for sleepable programs - Add RCU grace period chaining to BPF to wait for the completion of access from both sleepable and non-sleepable BPF programs - Add support storing struct task_struct objects as kptrs in maps - Improve helper UAPI by explicitly defining BPF_FUNC_xxx integer values - Add libbpf *_opts API-variants for bpf_*_get_fd_by_id() functions Protocols: - TCP: implement Protective Load Balancing across switch links - TCP: allow dynamically disabling TCP-MD5 static key, reverting back to fast[er]-path - UDP: Introduce optional per-netns hash lookup table - IPv6: simplify and cleanup sockets disposal - Netlink: support different type policies for each generic netlink operation - MPTCP: add MSG_FASTOPEN and FastOpen listener side support - MPTCP: add netlink notification support for listener sockets events - SCTP: add VRF support, allowing sctp sockets binding to VRF devices - Add bridging MAC Authentication Bypass (MAB) support - Extensions for Ethernet VPN bridging implementation to better support multicast scenarios - More work for Wi-Fi 7 support, comprising conversion of all the existing drivers to internal TX queue usage - IPSec: introduce a new offload type (packet offload) allowing complete header processing and crypto offloading - IPSec: extended ack support for more descriptive XFRM error reporting - RXRPC: increase SACK table size and move processing into a per-local endpoint kernel thread, reducing considerably the required locking - IEEE 802154: synchronous send frame and extended filtering support, initial support for scanning available 15.4 networks - Tun: bump the link speed from 10Mbps to 10Gbps - Tun/VirtioNet: implement UDP segmentation offload support Driver API: - PHY/SFP: improve power level switching between standard level 1 and the higher power levels - New API for netdev <-> devlink_port linkage - PTP: convert existing drivers to new frequency adjustment implementation - DSA: add support for rx offloading - Autoload DSA tagging driver when dynamically changing protocol - Add new PCP and APPTRUST attributes to Data Center Bridging - Add configuration support for 800Gbps link speed - Add devlink port function attribute to enable/disable RoCE and migratable - Extend devlink-rate to support strict prioriry and weighted fair queuing - Add devlink support to directly reading from region memory - New device tree helper to fetch MAC address from nvmem - New big TCP helper to simplify temporary header stripping New hardware / drivers: - Ethernet: - Marvel Octeon CNF95N and CN10KB Ethernet Switches - Marvel Prestera AC5X Ethernet Switch - WangXun 10 Gigabit NIC - Motorcomm yt8521 Gigabit Ethernet - Microchip ksz9563 Gigabit Ethernet Switch - Microsoft Azure Network Adapter - Linux Automation 10Base-T1L adapter - PHY: - Aquantia AQR112 and AQR412 - Motorcomm YT8531S - PTP: - Orolia ART-CARD - WiFi: - MediaTek Wi-Fi 7 (802.11be) devices - RealTek rtw8821cu, rtw8822bu, rtw8822cu and rtw8723du USB devices - Bluetooth: - Broadcom BCM4377/4378/4387 Bluetooth chipsets - Realtek RTL8852BE and RTL8723DS - Cypress.CYW4373A0 WiFi + Bluetooth combo device Drivers: - CAN: - gs_usb: bus error reporting support - kvaser_usb: listen only and bus error reporting support - Ethernet NICs: - Intel (100G): - extend action skbedit to RX queue mapping - implement devlink-rate support - support direct read from memory - nVidia/Mellanox (mlx5): - SW steering improvements, increasing rules update rate - Support for enhanced events compression - extend H/W offload packet manipulation capabilities - implement IPSec packet offload mode - nVidia/Mellanox (mlx4): - better big TCP support - Netronome Ethernet NICs (nfp): - IPsec offload support - add support for multicast filter - Broadcom: - RSS and PTP support improvements - AMD/SolarFlare: - netlink extened ack improvements - add basic flower matches to offload, and related stats - Virtual NICs: - ibmvnic: introduce affinity hint support - small / embedded: - FreeScale fec: add initial XDP support - Marvel mv643xx_eth: support MII/GMII/RGMII modes for Kirkwood - TI am65-cpsw: add suspend/resume support - Mediatek MT7986: add RX wireless wthernet dispatch support - Realtek 8169: enable GRO software interrupt coalescing per default - Ethernet high-speed switches: - Microchip (sparx5): - add support for Sparx5 TC/flower H/W offload via VCAP - Mellanox mlxsw: - add 802.1X and MAC Authentication Bypass offload support - add ip6gre support - Embedded Ethernet switches: - Mediatek (mtk_eth_soc): - improve PCS implementation, add DSA untag support - enable flow offload support - Renesas: - add rswitch R-Car Gen4 gPTP support - Microchip (lan966x): - add full XDP support - add TC H/W offload via VCAP - enable PTP on bridge interfaces - Microchip (ksz8): - add MTU support for KSZ8 series - Qualcomm 802.11ax WiFi (ath11k): - support configuring channel dwell time during scan - MediaTek WiFi (mt76): - enable Wireless Ethernet Dispatch (WED) offload support - add ack signal support - enable coredump support - remain_on_channel support - Intel WiFi (iwlwifi): - enable Wi-Fi 7 Extremely High Throughput (EHT) PHY capabilities - 320 MHz channels support - RealTek WiFi (rtw89): - new dynamic header firmware format support - wake-over-WLAN support" * tag 'net-next-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (2002 commits) ipvs: fix type warning in do_div() on 32 bit net: lan966x: Remove a useless test in lan966x_ptp_add_trap() net: ipa: add IPA v4.7 support dt-bindings: net: qcom,ipa: Add SM6350 compatible bnxt: Use generic HBH removal helper in tx path IPv6/GRO: generic helper to remove temporary HBH/jumbo header in driver selftests: forwarding: Add bridge MDB test selftests: forwarding: Rename bridge_mdb test bridge: mcast: Support replacement of MDB port group entries bridge: mcast: Allow user space to specify MDB entry routing protocol bridge: mcast: Allow user space to add (*, G) with a source list and filter mode bridge: mcast: Add support for (*, G) with a source list and filter mode bridge: mcast: Avoid arming group timer when (S, G) corresponds to a source bridge: mcast: Add a flag for user installed source entries bridge: mcast: Expose __br_multicast_del_group_src() bridge: mcast: Expose br_multicast_new_group_src() bridge: mcast: Add a centralized error path bridge: mcast: Place netlink policy before validation functions bridge: mcast: Split (*, G) and (S, G) addition into different functions bridge: mcast: Do not derive entry type from its filter mode ...
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+.. SPDX-License-Identifier: GPL-2.0-only
+.. Copyright (C) 2022 Red Hat, Inc.
+
+================================================
+BPF_MAP_TYPE_ARRAY and BPF_MAP_TYPE_PERCPU_ARRAY
+================================================
+
+.. note::
+ - ``BPF_MAP_TYPE_ARRAY`` was introduced in kernel version 3.19
+ - ``BPF_MAP_TYPE_PERCPU_ARRAY`` was introduced in version 4.6
+
+``BPF_MAP_TYPE_ARRAY`` and ``BPF_MAP_TYPE_PERCPU_ARRAY`` provide generic array
+storage. The key type is an unsigned 32-bit integer (4 bytes) and the map is
+of constant size. The size of the array is defined in ``max_entries`` at
+creation time. All array elements are pre-allocated and zero initialized when
+created. ``BPF_MAP_TYPE_PERCPU_ARRAY`` uses a different memory region for each
+CPU whereas ``BPF_MAP_TYPE_ARRAY`` uses the same memory region. The value
+stored can be of any size, however, all array elements are aligned to 8
+bytes.
+
+Since kernel 5.5, memory mapping may be enabled for ``BPF_MAP_TYPE_ARRAY`` by
+setting the flag ``BPF_F_MMAPABLE``. The map definition is page-aligned and
+starts on the first page. Sufficient page-sized and page-aligned blocks of
+memory are allocated to store all array values, starting on the second page,
+which in some cases will result in over-allocation of memory. The benefit of
+using this is increased performance and ease of use since userspace programs
+would not be required to use helper functions to access and mutate data.
+
+Usage
+=====
+
+Kernel BPF
+----------
+
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+ void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
+
+Array elements can be retrieved using the ``bpf_map_lookup_elem()`` helper.
+This helper returns a pointer into the array element, so to avoid data races
+with userspace reading the value, the user must use primitives like
+``__sync_fetch_and_add()`` when updating the value in-place.
+
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+ long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
+
+Array elements can be updated using the ``bpf_map_update_elem()`` helper.
+
+``bpf_map_update_elem()`` returns 0 on success, or negative error in case of
+failure.
+
+Since the array is of constant size, ``bpf_map_delete_elem()`` is not supported.
+To clear an array element, you may use ``bpf_map_update_elem()`` to insert a
+zero value to that index.
+
+Per CPU Array
+-------------
+
+Values stored in ``BPF_MAP_TYPE_ARRAY`` can be accessed by multiple programs
+across different CPUs. To restrict storage to a single CPU, you may use a
+``BPF_MAP_TYPE_PERCPU_ARRAY``.
+
+When using a ``BPF_MAP_TYPE_PERCPU_ARRAY`` the ``bpf_map_update_elem()`` and
+``bpf_map_lookup_elem()`` helpers automatically access the slot for the current
+CPU.
+
+bpf_map_lookup_percpu_elem()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+ void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key, u32 cpu)
+
+The ``bpf_map_lookup_percpu_elem()`` helper can be used to lookup the array
+value for a specific CPU. Returns value on success , or ``NULL`` if no entry was
+found or ``cpu`` is invalid.
+
+Concurrency
+-----------
+
+Since kernel version 5.1, the BPF infrastructure provides ``struct bpf_spin_lock``
+to synchronize access.
+
+Userspace
+---------
+
+Access from userspace uses libbpf APIs with the same names as above, with
+the map identified by its ``fd``.
+
+Examples
+========
+
+Please see the ``tools/testing/selftests/bpf`` directory for functional
+examples. The code samples below demonstrate API usage.
+
+Kernel BPF
+----------
+
+This snippet shows how to declare an array in a BPF program.
+
+.. code-block:: c
+
+ struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, u32);
+ __type(value, long);
+ __uint(max_entries, 256);
+ } my_map SEC(".maps");
+
+
+This example BPF program shows how to access an array element.
+
+.. code-block:: c
+
+ int bpf_prog(struct __sk_buff *skb)
+ {
+ struct iphdr ip;
+ int index;
+ long *value;
+
+ if (bpf_skb_load_bytes(skb, ETH_HLEN, &ip, sizeof(ip)) < 0)
+ return 0;
+
+ index = ip.protocol;
+ value = bpf_map_lookup_elem(&my_map, &index);
+ if (value)
+ __sync_fetch_and_add(value, skb->len);
+
+ return 0;
+ }
+
+Userspace
+---------
+
+BPF_MAP_TYPE_ARRAY
+~~~~~~~~~~~~~~~~~~
+
+This snippet shows how to create an array, using ``bpf_map_create_opts`` to
+set flags.
+
+.. code-block:: c
+
+ #include <bpf/libbpf.h>
+ #include <bpf/bpf.h>
+
+ int create_array()
+ {
+ int fd;
+ LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_MMAPABLE);
+
+ fd = bpf_map_create(BPF_MAP_TYPE_ARRAY,
+ "example_array", /* name */
+ sizeof(__u32), /* key size */
+ sizeof(long), /* value size */
+ 256, /* max entries */
+ &opts); /* create opts */
+ return fd;
+ }
+
+This snippet shows how to initialize the elements of an array.
+
+.. code-block:: c
+
+ int initialize_array(int fd)
+ {
+ __u32 i;
+ long value;
+ int ret;
+
+ for (i = 0; i < 256; i++) {
+ value = i;
+ ret = bpf_map_update_elem(fd, &i, &value, BPF_ANY);
+ if (ret < 0)
+ return ret;
+ }
+
+ return ret;
+ }
+
+This snippet shows how to retrieve an element value from an array.
+
+.. code-block:: c
+
+ int lookup(int fd)
+ {
+ __u32 index = 42;
+ long value;
+ int ret;
+
+ ret = bpf_map_lookup_elem(fd, &index, &value);
+ if (ret < 0)
+ return ret;
+
+ /* use value here */
+ assert(value == 42);
+
+ return ret;
+ }
+
+BPF_MAP_TYPE_PERCPU_ARRAY
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This snippet shows how to initialize the elements of a per CPU array.
+
+.. code-block:: c
+
+ int initialize_array(int fd)
+ {
+ int ncpus = libbpf_num_possible_cpus();
+ long values[ncpus];
+ __u32 i, j;
+ int ret;
+
+ for (i = 0; i < 256 ; i++) {
+ for (j = 0; j < ncpus; j++)
+ values[j] = i;
+ ret = bpf_map_update_elem(fd, &i, &values, BPF_ANY);
+ if (ret < 0)
+ return ret;
+ }
+
+ return ret;
+ }
+
+This snippet shows how to access the per CPU elements of an array value.
+
+.. code-block:: c
+
+ int lookup(int fd)
+ {
+ int ncpus = libbpf_num_possible_cpus();
+ __u32 index = 42, j;
+ long values[ncpus];
+ int ret;
+
+ ret = bpf_map_lookup_elem(fd, &index, &values);
+ if (ret < 0)
+ return ret;
+
+ for (j = 0; j < ncpus; j++) {
+ /* Use per CPU value here */
+ assert(values[j] == 42);
+ }
+
+ return ret;
+ }
+
+Semantics
+=========
+
+As shown in the example above, when accessing a ``BPF_MAP_TYPE_PERCPU_ARRAY``
+in userspace, each value is an array with ``ncpus`` elements.
+
+When calling ``bpf_map_update_elem()`` the flag ``BPF_NOEXIST`` can not be used
+for these maps.