€•'VŒsphinx.addnodes”Œdocument”“”)”}”(Œ rawsource”Œ”Œchildren”]”(Œ translations”Œ LanguagesNode”“”)”}”(hhh]”(hŒ pending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ refdomain”Œstd”Œreftype”Œdoc”Œ reftarget”Œ//translations/zh_CN/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuŒtagname”hhh ubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ//translations/zh_TW/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ//translations/it_IT/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ//translations/ja_JP/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ//translations/ko_KR/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ//translations/sp_SP/networking/radiotap-headers”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h hhŒ _document”hŒsource”NŒline”NubhŒcomment”“”)”}”(hŒ SPDX-License-Identifier: GPL-2.0”h]”hŒ SPDX-License-Identifier: GPL-2.0”…””}”hh£sbah}”(h]”h ]”h"]”h$]”h&]”Œ xml:space”Œpreserve”uh1h¡hhhžhhŸŒI/var/lib/git/docbuild/linux/Documentation/networking/radiotap-headers.rst”h KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒHow to use radiotap headers”h]”hŒHow to use radiotap headers”…””}”(hh»hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒ$Pointer to the radiotap include file”h]”hŒ$Pointer to the radiotap include file”…””}”(hhÌhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hhÉhžhhŸh³h KubhŒ paragraph”“”)”}”(hŒxRadiotap headers are variable-length and extensible, you can get most of the information you need to know on them from::”h]”hŒwRadiotap headers are variable-length and extensible, you can get most of the information you need to know on them from:”…””}”(hhÜhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K hhÉhžhubhŒ literal_block”“”)”}”(hŒ"./include/net/ieee80211_radiotap.h”h]”hŒ"./include/net/ieee80211_radiotap.h”…””}”hhìsbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1hêhŸh³h K hhÉhžhubhÛ)”}”(hŒ?This document gives an overview and warns on some corner cases.”h]”hŒ?This document gives an overview and warns on some corner cases.”…””}”(hhúhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KhhÉhžhubeh}”(h]”Œ$pointer-to-the-radiotap-include-file”ah ]”h"]”Œ$pointer to the radiotap include file”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒStructure of the header”h]”hŒStructure of the header”…””}”(hjhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjhžhhŸh³h KubhÛ)”}”(hXDThere 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.”h]”hXDThere 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.”…””}”(hj!hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h Khjhžhubhë)”}”(hŒf< 8-byte ieee80211_radiotap_header > [ ] [ ... ]”h]”hŒf< 8-byte ieee80211_radiotap_header > [ ] [ ... ]”…””}”hj/sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1hêhŸh³h KhjhžhubhÛ)”}”(hXNAt 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.”h]”hXRAt 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.”…””}”(hj=hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K!hjhžhubhÛ)”}”(hŒ‘Note also that the it_len member __le16 is set to the total number of bytes covered by the ieee80211_radiotap_header and any arguments following.”h]”hŒ‘Note also that the it_len member __le16 is set to the total number of bytes covered by the ieee80211_radiotap_header and any arguments following.”…””}”(hjKhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K'hjhžhubeh}”(h]”Œstructure-of-the-header”ah ]”h"]”Œstructure of the header”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒRequirements for arguments”h]”hŒRequirements for arguments”…””}”(hjdhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjahžhhŸh³h K,ubhÛ)”}”(hŒ¡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.”h]”hŒ¡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.”…””}”(hjrhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K.hjahžhubhŒ block_quote”“”)”}”(hX©- the arguments are all stored little-endian! - the argument payload for a given argument index has a fixed size. So IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is present. See the comments in ./include/net/ieee80211_radiotap.h for a nice breakdown of all the argument sizes - the arguments must be aligned to a boundary of the argument size using padding. So a u16 argument must start on the next u16 boundary if it isn't already on one, a u32 must start on the next u32 boundary and so on. - "alignment" is relative to the start of the ieee80211_radiotap_header, ie, the first byte of the radiotap header. The absolute alignment of that first byte isn't defined. So even if the whole radiotap header is starting at, eg, address 0x00000003, still the first byte of the radiotap header is treated as 0 for alignment purposes. - the above point that there may be no absolute alignment for multibyte entities in the fixed radiotap header or the argument region means that you have to take special evasive action when trying to access these multibyte entities. Some arches like Blackfin cannot deal with an attempt to dereference, eg, a u16 pointer that is pointing to an odd address. Instead you have to use a kernel API get_unaligned() to dereference the pointer, which will do it bytewise on the arches that require that. - The arguments for a given argument index can be a compound of multiple types together. For example IEEE80211_RADIOTAP_CHANNEL has an argument payload consisting of two u16s of total length 4. When this happens, the padding rule is applied dealing with a u16, NOT dealing with a 4-byte single entity. ”h]”hŒ bullet_list”“”)”}”(hhh]”(hŒ list_item”“”)”}”(hŒ,the arguments are all stored little-endian! ”h]”hÛ)”}”(hŒ+the arguments are all stored little-endian!”h]”hŒ+the arguments are all stored little-endian!”…””}”(hj‘hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K2hjubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubjŒ)”}”(hXthe argument payload for a given argument index has a fixed size. So IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is present. See the comments in ./include/net/ieee80211_radiotap.h for a nice breakdown of all the argument sizes ”h]”hÛ)”}”(hXthe argument payload for a given argument index has a fixed size. So IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is present. See the comments in ./include/net/ieee80211_radiotap.h for a nice breakdown of all the argument sizes”h]”hXthe argument payload for a given argument index has a fixed size. So IEEE80211_RADIOTAP_TSFT being present always indicates an 8-byte argument is present. See the comments in ./include/net/ieee80211_radiotap.h for a nice breakdown of all the argument sizes”…””}”(hj©hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K4hj¥ubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubjŒ)”}”(hŒØthe arguments must be aligned to a boundary of the argument size using padding. So a u16 argument must start on the next u16 boundary if it isn't already on one, a u32 must start on the next u32 boundary and so on. ”h]”hÛ)”}”(hŒ×the arguments must be aligned to a boundary of the argument size using padding. So a u16 argument must start on the next u16 boundary if it isn't already on one, a u32 must start on the next u32 boundary and so on.”h]”hŒÙthe arguments must be aligned to a boundary of the argument size using padding. So a u16 argument must start on the next u16 boundary if it isn’t already on one, a u32 must start on the next u32 boundary and so on.”…””}”(hjÁhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K9hj½ubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubjŒ)”}”(hXN"alignment" is relative to the start of the ieee80211_radiotap_header, ie, the first byte of the radiotap header. The absolute alignment of that first byte isn't defined. So even if the whole radiotap header is starting at, eg, address 0x00000003, still the first byte of the radiotap header is treated as 0 for alignment purposes. ”h]”hÛ)”}”(hXM"alignment" is relative to the start of the ieee80211_radiotap_header, ie, the first byte of the radiotap header. The absolute alignment of that first byte isn't defined. So even if the whole radiotap header is starting at, eg, address 0x00000003, still the first byte of the radiotap header is treated as 0 for alignment purposes.”h]”hXS“alignment†is relative to the start of the ieee80211_radiotap_header, ie, the first byte of the radiotap header. The absolute alignment of that first byte isn’t defined. So even if the whole radiotap header is starting at, eg, address 0x00000003, still the first byte of the radiotap header is treated as 0 for alignment purposes.”…””}”(hjÙhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h K=hjÕubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubjŒ)”}”(hXðthe above point that there may be no absolute alignment for multibyte entities in the fixed radiotap header or the argument region means that you have to take special evasive action when trying to access these multibyte entities. Some arches like Blackfin cannot deal with an attempt to dereference, eg, a u16 pointer that is pointing to an odd address. Instead you have to use a kernel API get_unaligned() to dereference the pointer, which will do it bytewise on the arches that require that. ”h]”hÛ)”}”(hXïthe above point that there may be no absolute alignment for multibyte entities in the fixed radiotap header or the argument region means that you have to take special evasive action when trying to access these multibyte entities. Some arches like Blackfin cannot deal with an attempt to dereference, eg, a u16 pointer that is pointing to an odd address. Instead you have to use a kernel API get_unaligned() to dereference the pointer, which will do it bytewise on the arches that require that.”h]”hXïthe above point that there may be no absolute alignment for multibyte entities in the fixed radiotap header or the argument region means that you have to take special evasive action when trying to access these multibyte entities. Some arches like Blackfin cannot deal with an attempt to dereference, eg, a u16 pointer that is pointing to an odd address. Instead you have to use a kernel API get_unaligned() to dereference the pointer, which will do it bytewise on the arches that require that.”…””}”(hjñhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KChjíubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubjŒ)”}”(hX/The arguments for a given argument index can be a compound of multiple types together. For example IEEE80211_RADIOTAP_CHANNEL has an argument payload consisting of two u16s of total length 4. When this happens, the padding rule is applied dealing with a u16, NOT dealing with a 4-byte single entity. ”h]”hÛ)”}”(hX-The arguments for a given argument index can be a compound of multiple types together. For example IEEE80211_RADIOTAP_CHANNEL has an argument payload consisting of two u16s of total length 4. When this happens, the padding rule is applied dealing with a u16, NOT dealing with a 4-byte single entity.”h]”hX-The arguments for a given argument index can be a compound of multiple types together. For example IEEE80211_RADIOTAP_CHANNEL has an argument payload consisting of two u16s of total length 4. When this happens, the padding rule is applied dealing with a u16, NOT dealing with a 4-byte single entity.”…””}”(hj hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KKhjubah}”(h]”h ]”h"]”h$]”h&]”uh1j‹hjˆubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1j†hŸh³h K2hj‚ubah}”(h]”h ]”h"]”h$]”h&]”uh1j€hŸh³h K2hjahžhubeh}”(h]”Œrequirements-for-arguments”ah ]”h"]”Œrequirements for arguments”ah$]”h&]”uh1h´hh¶hžhhŸh³h K,ubhµ)”}”(hhh]”(hº)”}”(hŒExample valid radiotap header”h]”hŒExample valid radiotap header”…””}”(hj6hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj3hžhhŸh³h KRubhë)”}”(hŒÉ0x00, 0x00, // <-- radiotap version + pad byte 0x0b, 0x00, // <- radiotap header length 0x04, 0x0c, 0x00, 0x00, // <-- bitmap 0x6c, // <-- rate (in 500kHz units) 0x0c, //<-- tx power 0x01 //<-- antenna”h]”hŒÉ0x00, 0x00, // <-- radiotap version + pad byte 0x0b, 0x00, // <- radiotap header length 0x04, 0x0c, 0x00, 0x00, // <-- bitmap 0x6c, // <-- rate (in 500kHz units) 0x0c, //<-- tx power 0x01 //<-- antenna”…””}”hjDsbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1hêhŸh³h KVhj3hžhubeh}”(h]”Œexample-valid-radiotap-header”ah ]”h"]”Œexample valid radiotap header”ah$]”h&]”uh1h´hh¶hžhhŸh³h KRubhµ)”}”(hhh]”(hº)”}”(hŒUsing the Radiotap Parser”h]”hŒUsing the Radiotap Parser”…””}”(hj]hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjZhžhhŸh³h K_ubhÛ)”}”(hŒçIf 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::”h]”hŒæIf 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:”…””}”(hjkhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KahjZhžhubhë)”}”(hX0#include /* 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; ... }”h]”hX0#include /* 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; ... }”…””}”hjysbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1hêhŸh³h KehjZhžhubhÛ)”}”(hŒAndy Green ”h]”(hŒ Andy Green <”…””}”(hj‡hžhhŸNh NubhŒ reference”“”)”}”(hŒandy@warmcat.com”h]”hŒandy@warmcat.com”…””}”(hj‘hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:andy@warmcat.com”uh1jhj‡ubhŒ>”…””}”(hj‡hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhŸh³h KŸhjZhžhubeh}”(h]”Œusing-the-radiotap-parser”ah ]”h"]”Œusing the radiotap parser”ah$]”h&]”uh1h´hh¶hžhhŸh³h K_ubeh}”(h]”Œhow-to-use-radiotap-headers”ah ]”h"]”Œhow to use radiotap headers”ah$]”h&]”uh1h´hhhžhhŸh³h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h³uh1hŒcurrent_source”NŒ current_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¹NŒ generator”NŒ datestamp”NŒ source_link”NŒ source_url”NŒ toc_backlinks”Œentry”Œfootnote_backlinks”KŒ sectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒ strip_classes”NŒ report_level”KŒ halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ traceback”ˆŒinput_encoding”Œ utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jÞŒerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œ language_code”Œen”Œrecord_dependencies”NŒconfig”NŒ id_prefix”hŒauto_id_prefix”Œid”Œ dump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h³Œ _destination”NŒ _config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒ raw_enabled”KŒline_length_limit”M'Œpep_references”NŒ pep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒ rfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œ smart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œ docinfo_xform”KŒsectsubtitle_xform”‰Œ image_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(j¸jµj j j^j[j0j-jWjTj°j­uŒ nametypes”}”(j¸‰j ‰j^‰j0‰jW‰j°‰uh}”(jµh¶j hÉj[jj-jajTj3j­jZuŒ footnote_refs”}”Œ citation_refs”}”Œ autofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ footnotes”]”Œ citations”]”Œautofootnote_start”KŒsymbol_footnote_start”KŒ id_counter”Œ collections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”Œ transformer”NŒ include_log”]”Œ decoration”Nhžhub.