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| -rw-r--r-- | Documentation/networking/ethtool-netlink.rst | 84 |
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diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst index 9448442ad293..7797f1237472 100644 --- a/Documentation/networking/ethtool-netlink.rst +++ b/Documentation/networking/ethtool-netlink.rst @@ -76,6 +76,90 @@ of the flag should be interpreted the way the client expects. A client must not set flags it does not understand. +Bit sets +======== + +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). + +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 +request) or at least a second request (when the bitset is in a reply). This is +useful for one shot applications like traditional ethtool command. On the +other hand, long running applications like ethtool monitor (displaying +notifications) or network management daemons may prefer fetching the names +only once and using compact form to save message size. Notifications from +ethtool netlink interface always use compact form for bitsets. + +A bitset can represent either a value/mask pair (``ETHTOOL_A_BITSET_NOMASK`` +not set) or a single bitmap (``ETHTOOL_A_BITSET_NOMASK`` set). In requests +modifying a bitmap, the former changes the bit set in mask to values set in +value and preserves the rest; the latter sets the bits set in the bitmap and +clears the rest. + +Compact form: nested (bitset) atrribute contents: + + ============================ ====== ============================ + ``ETHTOOL_A_BITSET_NOMASK`` flag no mask, only a list + ``ETHTOOL_A_BITSET_SIZE`` u32 number of significant bits + ``ETHTOOL_A_BITSET_VALUE`` binary bitmap of bit values + ``ETHTOOL_A_BITSET_MASK`` binary bitmap of valid bits + ============================ ====== ============================ + +Value and mask must have length at least ``ETHTOOL_A_BITSET_SIZE`` bits +rounded up to a multiple of 32 bits. They consist of 32-bit words in host byte +order, words ordered from least significant to most significant (i.e. the same +way as bitmaps are passed with ioctl interface). + +For compact form, ``ETHTOOL_A_BITSET_SIZE`` and ``ETHTOOL_A_BITSET_VALUE`` are +mandatory. ``ETHTOOL_A_BITSET_MASK`` attribute is mandatory if +``ETHTOOL_A_BITSET_NOMASK`` is not set (bitset represents a value/mask pair); +if ``ETHTOOL_A_BITSET_NOMASK`` is not set, ``ETHTOOL_A_BITSET_MASK`` is not +allowed (bitset represents a single bitmap. + +Kernel bit set length may differ from userspace length if older application is +used on newer kernel or vice versa. If userspace bitmap is longer, an error is +issued only if the request actually tries to set values of some bits not +recognized by kernel. + +Bit-by-bit form: nested (bitset) attribute contents: + + +------------------------------------+--------+-----------------------------+ + | ``ETHTOOL_A_BITSET_NOMASK`` | flag | no mask, only a list | + +------------------------------------+--------+-----------------------------+ + | ``ETHTOOL_A_BITSET_SIZE`` | u32 | number of significant bits | + +------------------------------------+--------+-----------------------------+ + | ``ETHTOOL_A_BITSET_BITS`` | nested | array of bits | + +-+----------------------------------+--------+-----------------------------+ + | | ``ETHTOOL_A_BITSET_BITS_BIT+`` | nested | one bit | + +-+-+--------------------------------+--------+-----------------------------+ + | | | ``ETHTOOL_A_BITSET_BIT_INDEX`` | u32 | bit index (0 for LSB) | + +-+-+--------------------------------+--------+-----------------------------+ + | | | ``ETHTOOL_A_BITSET_BIT_NAME`` | string | bit name | + +-+-+--------------------------------+--------+-----------------------------+ + | | | ``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 +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. + +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 +such case. Such bitset represents a bitmap with listed bits set and the rest +zero. + +In requests, application can use either form. Form used by kernel in reply is +determined by ``ETHTOOL_FLAG_COMPACT_BITSETS`` flag in flags field of request +header. Semantics of value and mask depends on the attribute. + + List of message types ===================== |