kernel/linux.git/Documentation/userspace-api/netlink, branch v6.6.132

netlink: add variable-length / auto integers

2025-09-09T16:56:22+00:00

[ Upstream commit 374d345d9b5e13380c66d7042f9533a6ac6d1195 ] We currently push everyone to use padding to align 64b values in netlink. Un-padded nla_put_u64() doesn't even exist any more. The story behind this possibly start with this thread: https://lore.kernel.org/netdev/20121204.130914.1457976839967676240.davem@davemloft.net/ where DaveM was concerned about the alignment of a structure containing 64b stats. If user space tries to access such struct directly: struct some_stats *stats = nla_data(attr); printf("A: %llu", stats->a); lack of alignment may become problematic for some architectures. These days we most often put every single member in a separate attribute, meaning that the code above would use a helper like nla_get_u64(), which can deal with alignment internally. Even for arches which don't have good unaligned access - access aligned to 4B should be pretty efficient. Kernel and well known libraries deal with unaligned input already. Padded 64b is quite space-inefficient (64b + pad means at worst 16B per attr vs 32b which takes 8B). It is also more typing: if (nla_put_u64_pad(rsp, NETDEV_A_SOMETHING_SOMETHING, value, NETDEV_A_SOMETHING_PAD)) Create a new attribute type which will use 32 bits at netlink level if value is small enough (probably most of the time?), and (4B-aligned) 64 bits otherwise. Kernel API is just: if (nla_put_uint(rsp, NETDEV_A_SOMETHING_SOMETHING, value)) Calling this new type "just" sint / uint with no specific size will hopefully also make people more comfortable with using it. Currently telling people "don't use u8, you may need the bits, and netlink will round up to 4B, anyway" is the #1 comment we give to newcomers. In terms of netlink layout it looks like this: 0 4 8 12 16 32b: [nlattr][ u32 ] 64b: [ pad ][nlattr][ u64 ] uint(32) [nlattr][ u32 ] uint(64) [nlattr][ u64 ] Signed-off-by: Jakub Kicinski Acked-by: Nicolas Dichtel Signed-off-by: David S. Miller Stable-dep-of: 030e1c456666 ("macsec: read MACSEC_SA_ATTR_PN with nla_get_uint") Signed-off-by: Sasha Levin

Merge tag 'net-6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2023-09-08T01:33:07+00:00

Pull networking updates from Jakub Kicinski: "Including fixes from netfilter and bpf. Current release - regressions: - eth: stmmac: fix failure to probe without MAC interface specified Current release - new code bugs: - docs: netlink: fix missing classic_netlink doc reference Previous releases - regressions: - deal with integer overflows in kmalloc_reserve() - use sk_forward_alloc_get() in sk_get_meminfo() - bpf_sk_storage: fix the missing uncharge in sk_omem_alloc - fib: avoid warn splat in flow dissector after packet mangling - skb_segment: call zero copy functions before using skbuff frags - eth: sfc: check for zero length in EF10 RX prefix Previous releases - always broken: - af_unix: fix msg_controllen test in scm_pidfd_recv() for MSG_CMSG_COMPAT - xsk: fix xsk_build_skb() dereferencing possible ERR_PTR() - netfilter: - nft_exthdr: fix non-linear header modification - xt_u32, xt_sctp: validate user space input - nftables: exthdr: fix 4-byte stack OOB write - nfnetlink_osf: avoid OOB read - one more fix for the garbage collection work from last release - igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU - bpf, sockmap: fix preempt_rt splat when using raw_spin_lock_t - handshake: fix null-deref in handshake_nl_done_doit() - ip: ignore dst hint for multipath routes to ensure packets are hashed across the nexthops - phy: micrel: - correct bit assignments for cable test errata - disable EEE according to the KSZ9477 errata Misc: - docs/bpf: document compile-once-run-everywhere (CO-RE) relocations - Revert "net: macsec: preserve ingress frame ordering", it appears to have been developed against an older kernel, problem doesn't exist upstream" * tag 'net-6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (95 commits) net: enetc: distinguish error from valid pointers in enetc_fixup_clear_rss_rfs() Revert "net: team: do not use dynamic lockdep key" net: hns3: remove GSO partial feature bit net: hns3: fix the port information display when sfp is absent net: hns3: fix invalid mutex between tc qdisc and dcb ets command issue net: hns3: fix debugfs concurrency issue between kfree buffer and read net: hns3: fix byte order conversion issue in hclge_dbg_fd_tcam_read() net: hns3: Support query tx timeout threshold by debugfs net: hns3: fix tx timeout issue net: phy: Provide Module 4 KSZ9477 errata (DS80000754C) netfilter: nf_tables: Unbreak audit log reset netfilter: ipset: add the missing IP_SET_HASH_WITH_NET0 macro for ip_set_hash_netportnet.c netfilter: nft_set_rbtree: skip sync GC for new elements in this transaction netfilter: nf_tables: uapi: Describe NFTA_RULE_CHAIN_ID netfilter: nfnetlink_osf: avoid OOB read netfilter: nftables: exthdr: fix 4-byte stack OOB write selftests/bpf: Check bpf_sk_storage has uncharged sk_omem_alloc bpf: bpf_sk_storage: Fix the missing uncharge in sk_omem_alloc bpf: bpf_sk_storage: Fix invalid wait context lockdep report s390/bpf: Pass through tail call counter in trampolines ...

Merge tag 'docs-6.6' of git://git.lwn.net/linux

2023-08-31T03:05:42+00:00

Pull documentation updates from Jonathan Corbet: "Documentation work keeps chugging along; this includes: - Work from Carlos Bilbao to integrate rustdoc output into the generated HTML documentation. This took some work to figure out how to do it without slowing the docs build and without creating people who don't have Rust installed, but Carlos got there - Move the loongarch and mips architecture documentation under Documentation/arch/ - Some more maintainer documentation from Jakub ... plus the usual assortment of updates, translations, and fixes" * tag 'docs-6.6' of git://git.lwn.net/linux: (56 commits) Docu: genericirq.rst: fix irq-example input: docs: pxrc: remove reference to phoenix-sim Documentation: serial-console: Fix literal block marker docs/mm: remove references to hmm_mirror ops and clean typos docs/zh_CN: correct regi_chg(),regi_add() to region_chg(),region_add() Documentation: Fix typos Documentation/ABI: Fix typos scripts: kernel-doc: fix macro handling in enums scripts: kernel-doc: parse DEFINE_DMA_UNMAP_[ADDR|LEN] Documentation: riscv: Update boot image header since EFI stub is supported Documentation: riscv: Add early boot document Documentation: arm: Add bootargs to the table of added DT parameters docs: kernel-parameters: Refer to the correct bitmap function doc: update params of memhp_default_state= docs: Add book to process/kernel-docs.rst docs: sparse: fix invalid link addresses docs: vfs: clean up after the iterate() removal docs: Add a section on surveys to the researcher guidelines docs: move mips under arch docs: move loongarch under arch ...

doc/netlink: Fix missing classic_netlink doc reference

2023-08-31T01:32:28+00:00

Add missing cross-reference label for classic_netlink. Fixes: 2db8abf0b455 ("doc/netlink: Document the netlink-raw schema extensions") Signed-off-by: Donald Hunter Link: https://lore.kernel.org/r/20230829085539.36354-1-donald.hunter@gmail.com Signed-off-by: Jakub Kicinski

doc/netlink: Document the netlink-raw schema extensions

2023-08-28T00:17:10+00:00

Add a doc page for netlink-raw that describes the schema attributes needed for netlink-raw. Signed-off-by: Donald Hunter Reviewed-by: Jacob Keller Link: https://lore.kernel.org/r/20230825122756.7603-5-donald.hunter@gmail.com Signed-off-by: Jakub Kicinski

doc/netlink: Update genetlink-legacy documentation

2023-08-28T00:17:09+00:00

Add documentation for recently added genetlink-legacy schema attributes. Remove statements about 'work in progress' and 'todo'. Signed-off-by: Donald Hunter Reviewed-by: Jacob Keller Link: https://lore.kernel.org/r/20230825122756.7603-4-donald.hunter@gmail.com Signed-off-by: Jakub Kicinski

Documentation: Fix typos

2023-08-18T17:29:03+00:00

Fix typos in Documentation. Signed-off-by: Bjorn Helgaas Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org Signed-off-by: Jonathan Corbet

tools: ynl: user space helpers

2023-06-06T19:31:31+00:00

Add "fixed" part of the user space Netlink Spec-based library. This will get linked with the protocol implementations to form a full API. Acked-by: Willem de Bruijn Signed-off-by: Jakub Kicinski

docs: netlink: document the sub-type attribute property

2023-03-29T06:54:43+00:00

Add a definition for sub-type to the protocol spec doc and a description of its usage for C arrays in genetlink-legacy. Signed-off-by: Donald Hunter Reviewed-by: Bagas Sanjaya Signed-off-by: Jakub Kicinski

docs: netlink: document struct support for genetlink-legacy

2023-03-29T06:54:43+00:00

Describe the genetlink-legacy support for using struct definitions for fixed headers and for binary attributes. Signed-off-by: Donald Hunter Reviewed-by: Bagas Sanjaya Signed-off-by: Jakub Kicinski