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docs: ethtool: clarify the bit-by-bit bitset format description

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Clarify the bit-by-bit bitset format's behavior around mandatory
attributes and bit identification. More specifically, the following
changes are made:

* Rephrase a misleading sentence which implies name and index are
  mutually exclusive
* Describe that ETHTOOL_A_BITSET_BITS nest is mandatory
* Describe that a request fails if inconsistent identifiers are given

Signed-off-by: Yohei Kojima <yk@y-koj.net>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/ef90a56965ca66e57aa177929ce3e10c5ca815fa.1772031974.git.yk@y-koj.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yohei Kojima
2026-02-26 00:12:09 +09:00
committed by Jakub Kicinski
parent f22b4e6fbb
commit 5cf47393d9
1 changed files with 8 additions and 4 deletions
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12
Documentation/networking/ethtool-netlink.rst
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@@ -96,7 +96,7 @@ For short bitmaps of (reasonably) fixed length, standard ``NLA_BITFIELD32``
type is used. For arbitrary length bitmaps, ethtool netlink uses a nested
attribute with contents of one of two forms: compact (two binary bitmaps
representing bit values and mask of affected bits) and bit-by-bit (list of
bits identified by either index or name).
bits identified by index or name).
Verbose (bit-by-bit) bitsets allow sending symbolic names for bits together
with their values which saves a round trip (when the bitset is passed in a
@@ -156,12 +156,16 @@ Bit-by-bit form: nested (bitset) attribute contents:
| | | ``ETHTOOL_A_BITSET_BIT_VALUE`` | flag | present if bit is set |
+-+-+--------------------------------+--------+-----------------------------+
Bit size is optional for bit-by-bit form. ``ETHTOOL_A_BITSET_BITS`` nest can
For bit-by-bit form, ``ETHTOOL_A_BITSET_SIZE`` is optional, and
``ETHTOOL_A_BITSET_BITS`` is mandatory. ``ETHTOOL_A_BITSET_BITS`` nest can
only contain ``ETHTOOL_A_BITSET_BITS_BIT`` attributes but there can be an
arbitrary number of them. A bit may be identified by its index or by its
name. When used in requests, listed bits are set to 0 or 1 according to
``ETHTOOL_A_BITSET_BIT_VALUE``, the rest is preserved. A request fails if
index exceeds kernel bit length or if name is not recognized.
``ETHTOOL_A_BITSET_BIT_VALUE``, the rest is preserved.
A request fails if index exceeds kernel bit length or if name is not
recognized. If both name and index are set, the request will fail if they
point to different bits.
When ``ETHTOOL_A_BITSET_NOMASK`` flag is present, bitset is interpreted as
a simple bitmap. ``ETHTOOL_A_BITSET_BIT_VALUE`` attributes are not used in