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author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-06-03 16:27:18 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-06-03 16:27:18 -0700 |
commit | cb8e59cc87201af93dfbb6c3dccc8fcad72a09c2 (patch) | |
tree | a334db9022f89654b777bbce8c4c6632e65b9031 /Documentation/networking/radiotap-headers.rst | |
parent | 2e63f6ce7ed2c4ff83ba30ad9ccad422289a6c63 (diff) | |
parent | 065fcfd49763ec71ae345bb5c5a74f961031e70e (diff) | |
download | linux-cb8e59cc87201af93dfbb6c3dccc8fcad72a09c2.tar.bz2 |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next
Pull networking updates from David Miller:
1) Allow setting bluetooth L2CAP modes via socket option, from Luiz
Augusto von Dentz.
2) Add GSO partial support to igc, from Sasha Neftin.
3) Several cleanups and improvements to r8169 from Heiner Kallweit.
4) Add IF_OPER_TESTING link state and use it when ethtool triggers a
device self-test. From Andrew Lunn.
5) Start moving away from custom driver versions, use the globally
defined kernel version instead, from Leon Romanovsky.
6) Support GRO vis gro_cells in DSA layer, from Alexander Lobakin.
7) Allow hard IRQ deferral during NAPI, from Eric Dumazet.
8) Add sriov and vf support to hinic, from Luo bin.
9) Support Media Redundancy Protocol (MRP) in the bridging code, from
Horatiu Vultur.
10) Support netmap in the nft_nat code, from Pablo Neira Ayuso.
11) Allow UDPv6 encapsulation of ESP in the ipsec code, from Sabrina
Dubroca. Also add ipv6 support for espintcp.
12) Lots of ReST conversions of the networking documentation, from Mauro
Carvalho Chehab.
13) Support configuration of ethtool rxnfc flows in bcmgenet driver,
from Doug Berger.
14) Allow to dump cgroup id and filter by it in inet_diag code, from
Dmitry Yakunin.
15) Add infrastructure to export netlink attribute policies to
userspace, from Johannes Berg.
16) Several optimizations to sch_fq scheduler, from Eric Dumazet.
17) Fallback to the default qdisc if qdisc init fails because otherwise
a packet scheduler init failure will make a device inoperative. From
Jesper Dangaard Brouer.
18) Several RISCV bpf jit optimizations, from Luke Nelson.
19) Correct the return type of the ->ndo_start_xmit() method in several
drivers, it's netdev_tx_t but many drivers were using
'int'. From Yunjian Wang.
20) Add an ethtool interface for PHY master/slave config, from Oleksij
Rempel.
21) Add BPF iterators, from Yonghang Song.
22) Add cable test infrastructure, including ethool interfaces, from
Andrew Lunn. Marvell PHY driver is the first to support this
facility.
23) Remove zero-length arrays all over, from Gustavo A. R. Silva.
24) Calculate and maintain an explicit frame size in XDP, from Jesper
Dangaard Brouer.
25) Add CAP_BPF, from Alexei Starovoitov.
26) Support terse dumps in the packet scheduler, from Vlad Buslov.
27) Support XDP_TX bulking in dpaa2 driver, from Ioana Ciornei.
28) Add devm_register_netdev(), from Bartosz Golaszewski.
29) Minimize qdisc resets, from Cong Wang.
30) Get rid of kernel_getsockopt and kernel_setsockopt in order to
eliminate set_fs/get_fs calls. From Christoph Hellwig.
* git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (2517 commits)
selftests: net: ip_defrag: ignore EPERM
net_failover: fixed rollback in net_failover_open()
Revert "tipc: Fix potential tipc_aead refcnt leak in tipc_crypto_rcv"
Revert "tipc: Fix potential tipc_node refcnt leak in tipc_rcv"
vmxnet3: allow rx flow hash ops only when rss is enabled
hinic: add set_channels ethtool_ops support
selftests/bpf: Add a default $(CXX) value
tools/bpf: Don't use $(COMPILE.c)
bpf, selftests: Use bpf_probe_read_kernel
s390/bpf: Use bcr 0,%0 as tail call nop filler
s390/bpf: Maintain 8-byte stack alignment
selftests/bpf: Fix verifier test
selftests/bpf: Fix sample_cnt shared between two threads
bpf, selftests: Adapt cls_redirect to call csum_level helper
bpf: Add csum_level helper for fixing up csum levels
bpf: Fix up bpf_skb_adjust_room helper's skb csum setting
sfc: add missing annotation for efx_ef10_try_update_nic_stats_vf()
crypto/chtls: IPv6 support for inline TLS
Crypto/chcr: Fixes a coccinile check error
Crypto/chcr: Fixes compilations warnings
...
Diffstat (limited to 'Documentation/networking/radiotap-headers.rst')
-rw-r--r-- | Documentation/networking/radiotap-headers.rst | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/Documentation/networking/radiotap-headers.rst b/Documentation/networking/radiotap-headers.rst new file mode 100644 index 000000000000..1a1bd1ec0650 --- /dev/null +++ b/Documentation/networking/radiotap-headers.rst @@ -0,0 +1,159 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========================== +How to use radiotap headers +=========================== + +Pointer to the radiotap include file +------------------------------------ + +Radiotap headers are variable-length and extensible, you can get most of the +information you need to know on them from:: + + ./include/net/ieee80211_radiotap.h + +This document gives an overview and warns on some corner cases. + + +Structure of the header +----------------------- + +There is a fixed portion at the start which contains a u32 bitmap that defines +if the possible argument associated with that bit is present or not. So if b0 +of the it_present member of ieee80211_radiotap_header is set, it means that +the header for argument index 0 (IEEE80211_RADIOTAP_TSFT) is present in the +argument area. + +:: + + < 8-byte ieee80211_radiotap_header > + [ <possible argument bitmap extensions ... > ] + [ <argument> ... ] + +At the moment there are only 13 possible argument indexes defined, but in case +we run out of space in the u32 it_present member, it is defined that b31 set +indicates that there is another u32 bitmap following (shown as "possible +argument bitmap extensions..." above), and the start of the arguments is moved +forward 4 bytes each time. + +Note also that the it_len member __le16 is set to the total number of bytes +covered by the ieee80211_radiotap_header and any arguments following. + + +Requirements for arguments +-------------------------- + +After the fixed part of the header, the arguments follow for each argument +index whose matching bit is set in the it_present member of +ieee80211_radiotap_header. + + - the arguments are all stored little-endian! + + - the argument payload for a given argument index has a fixed size. So + IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is + present. See the comments in ./include/net/ieee80211_radiotap.h for a nice + breakdown of all the argument sizes + + - the arguments must be aligned to a boundary of the argument size using + padding. So a u16 argument must start on the next u16 boundary if it isn't + already on one, a u32 must start on the next u32 boundary and so on. + + - "alignment" is relative to the start of the ieee80211_radiotap_header, ie, + the first byte of the radiotap header. The absolute alignment of that first + byte isn't defined. So even if the whole radiotap header is starting at, eg, + address 0x00000003, still the first byte of the radiotap header is treated as + 0 for alignment purposes. + + - the above point that there may be no absolute alignment for multibyte + entities in the fixed radiotap header or the argument region means that you + have to take special evasive action when trying to access these multibyte + entities. Some arches like Blackfin cannot deal with an attempt to + dereference, eg, a u16 pointer that is pointing to an odd address. Instead + you have to use a kernel API get_unaligned() to dereference the pointer, + which will do it bytewise on the arches that require that. + + - The arguments for a given argument index can be a compound of multiple types + together. For example IEEE80211_RADIOTAP_CHANNEL has an argument payload + consisting of two u16s of total length 4. When this happens, the padding + rule is applied dealing with a u16, NOT dealing with a 4-byte single entity. + + +Example valid radiotap header +----------------------------- + +:: + + 0x00, 0x00, // <-- radiotap version + pad byte + 0x0b, 0x00, // <- radiotap header length + 0x04, 0x0c, 0x00, 0x00, // <-- bitmap + 0x6c, // <-- rate (in 500kHz units) + 0x0c, //<-- tx power + 0x01 //<-- antenna + + +Using the Radiotap Parser +------------------------- + +If you are having to parse a radiotap struct, you can radically simplify the +job by using the radiotap parser that lives in net/wireless/radiotap.c and has +its prototypes available in include/net/cfg80211.h. You use it like this:: + + #include <net/cfg80211.h> + + /* buf points to the start of the radiotap header part */ + + int MyFunction(u8 * buf, int buflen) + { + int pkt_rate_100kHz = 0, antenna = 0, pwr = 0; + struct ieee80211_radiotap_iterator iterator; + int ret = ieee80211_radiotap_iterator_init(&iterator, buf, buflen); + + while (!ret) { + + ret = ieee80211_radiotap_iterator_next(&iterator); + + if (ret) + continue; + + /* see if this argument is something we can use */ + + switch (iterator.this_arg_index) { + /* + * You must take care when dereferencing iterator.this_arg + * for multibyte types... the pointer is not aligned. Use + * get_unaligned((type *)iterator.this_arg) to dereference + * iterator.this_arg for type "type" safely on all arches. + */ + case IEEE80211_RADIOTAP_RATE: + /* radiotap "rate" u8 is in + * 500kbps units, eg, 0x02=1Mbps + */ + pkt_rate_100kHz = (*iterator.this_arg) * 5; + break; + + case IEEE80211_RADIOTAP_ANTENNA: + /* radiotap uses 0 for 1st ant */ + antenna = *iterator.this_arg); + break; + + case IEEE80211_RADIOTAP_DBM_TX_POWER: + pwr = *iterator.this_arg; + break; + + default: + break; + } + } /* while more rt headers */ + + if (ret != -ENOENT) + return TXRX_DROP; + + /* discard the radiotap header part */ + buf += iterator.max_length; + buflen -= iterator.max_length; + + ... + + } + +Andy Green <andy@warmcat.com> |