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Message-ID: <f43999612ed9d17fb7fe8f21e777e1c784f23c46.1770457868.git.yk@y-koj.net> Date: Sat, 7 Feb 2026 19:25:38 +0900 From: Yohei Kojima <yk@...oj.net> To: Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net> Cc: Yohei Kojima <yk@...oj.net>, netdev@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH net-next v2] docs: ethtool: clarify the bit-by-bit bitset format description 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@...oj.net> --- Current ethtool-netlink documentation doesn't describe several behavior around bit-by-bit bitset, which makes it hard to develop a ethtool library without digging into the kernel code. This patch eases the gap between the kernel behavior and the documentation by adding descriptions around the mandatory attribute and bit identification. ChangeLog ========= v2 (this version): * Minimize the diff for ease of review v1: https://lore.kernel.org/lkml/e9ea0fe8bf7935d6439e4dc883414b685afbaf58.1770045398.git.yk@y-koj.net/ --- Documentation/networking/ethtool-netlink.rst | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst index af56c304cef4..32179168eb73 100644 --- a/Documentation/networking/ethtool-netlink.rst +++ b/Documentation/networking/ethtool-netlink.rst @@ -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 -- 2.52.0
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