docs: networking: convert radiotap-headers.txt to ReST

- add SPDX header;
- adjust title markup;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines where needed;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 152 deletions

diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
deleted file mode 100644
index 953331c7984f..000000000000
--- a/Documentation/networking/radiotap-headers.txt
+++ /dev/null
@@ -1,152 +0,0 @@
-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>