From: Jiri Pirko <jiri@resnulli.us>
To: Michal Kubecek <mkubecek@suse.cz>
Cc: netdev@vger.kernel.org, David Miller <davem@davemloft.net>,
Jakub Kicinski <jakub.kicinski@netronome.com>,
Andrew Lunn <andrew@lunn.ch>,
Florian Fainelli <f.fainelli@gmail.com>,
John Linville <linville@tuxdriver.com>,
Stephen Hemminger <stephen@networkplumber.org>,
Johannes Berg <johannes@sipsolutions.net>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v6 06/15] ethtool: netlink bitset handling
Date: Thu, 4 Jul 2019 10:04:35 +0200 [thread overview]
Message-ID: <20190704080435.GF2250@nanopsycho> (raw)
In-Reply-To: <20190703181851.GP20101@unicorn.suse.cz>
Wed, Jul 03, 2019 at 08:18:51PM CEST, mkubecek@suse.cz wrote:
>On Wed, Jul 03, 2019 at 01:49:33PM +0200, Jiri Pirko wrote:
>> Tue, Jul 02, 2019 at 01:50:09PM CEST, mkubecek@suse.cz wrote:
>> >diff --git a/Documentation/networking/ethtool-netlink.txt b/Documentation/networking/ethtool-netlink.txt
>> >index 97c369aa290b..4636682c551f 100644
>> >--- a/Documentation/networking/ethtool-netlink.txt
>> >+++ b/Documentation/networking/ethtool-netlink.txt
>> >@@ -73,6 +73,67 @@ set, the behaviour is the same as (or closer to) the behaviour before it was
>> > introduced.
>> >
>> >
>> >+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).
>> >+
>> >+Compact form: nested (bitset) atrribute contents:
>> >+
>> >+ ETHTOOL_A_BITSET_LIST (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,
>>
>> Looks like the blocks are similar to NLA_BITFIELD32. Why don't you user
>> nested array of NLA_BITFIELD32 instead?
>
>That would mean a layout like
>
> 4 bytes of attr header
> 4 bytes of value
> 4 bytes of mask
> 4 bytes of attr header
> 4 bytes of value
> 4 bytes of mask
> ...
>
>i.e. interleaved headers, words of value and words of mask. Having value
>and mask contiguous looks cleaner to me. Also, I can quickly check the
>sizes without iterating through a (potentially long) array.
Yeah, if you are not happy with this, I suggest to introduce
NLA_BITFIELD with arbitrary size. That would be probably cleanest.
>
>> >+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. Similar to BITFIELD32, a compact form bit set requests to set bits
>>
>> Double space^^
>
>Hm, I have to learn how to tell vim not to do that with "gq".
>
>> >+in the mask to 1 (if the bit is set in value) or 0 (if not) and preserve the
>> >+rest. If ETHTOOL_A_BITSET_LIST is present, there is no mask and bitset
>> >+represents a simple list of bits.
>>
>> Okay, that is a bit confusing. Why not to rename to something like:
>> ETHTOOL_A_BITSET_NO_MASK (flag)
>> ?
>
>From the logical point of view, it's used for lists - list of link
>modes, list of netdev features, list of timestamping modes etc.
>
>The point is that in userspace requests, we sometimes want to change
>some values (enable A, disable B), sometimes to define the list of
>values to be set (I want (only) A, C and E to be enabled). In kernel
>replies, sometimes there is a natural value/mask pairing (e.g.
>advertised and supported link modes, enabled and supported WoL modes)
>but often there is just one 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_LIST (flag) no mask, only a list
>> >+ ETHTOOL_A_BITSET_SIZE (u32) number of significant bits
>> >+ ETHTOOL_A_BITSET_BIT (nested) array of bits
>> >+ ETHTOOL_A_BITSET_BIT+ (nested) one bit
>> >+ ETHTOOL_A_BIT_INDEX (u32) bit index (0 for LSB)
>> >+ ETHTOOL_A_BIT_NAME (string) bit name
>> >+ ETHTOOL_A_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_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_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_LIST flag is present, bitset is interpreted as a simple
>> >+bit list. ETHTOOL_A_BIT_VALUE attributes are not used in such case. Bit list
>> >+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 a flag in flags field of request header. Semantics of value and
>> >+mask depends on the attribute. General idea is that flags control request
>> >+processing, info_mask control which parts of the information are returned in
>> >+"get" request and index identifies a particular subcommand or an object to
>> >+which the request applies.
>>
>> This is quite complex and confusing. Having the same API for 2 APIs is
>> odd. The API should be crystal clear, easy to use.
>>
>> Why can't you have 2 commands, one working with bit arrays only, one
>> working with strings? Something like:
>> X_GET
>> ETHTOOL_A_BITS (nested)
>> ETHTOOL_A_BIT_ARRAY (BITFIELD32)
>> X_NAMES_GET
>> ETHTOOL_A_BIT_NAMES (nested)
>> ETHTOOL_A_BIT_INDEX
>> ETHTOOL_A_BIT_NAME
>>
>> For set, you can also have multiple cmds:
>> X_SET - to set many at once, by bit index
>> ETHTOOL_A_BITS (nested)
>> ETHTOOL_A_BIT_ARRAY (BITFIELD32)
>> X_ONE_SET - to set one, by bit index
>> ETHTOOL_A_BIT_INDEX
>> ETHTOOL_A_BIT_VALUE
>> X_ONE_SET - to set one, by name
>> ETHTOOL_A_BIT_NAME
>> ETHTOOL_A_BIT_VALUE
>
>This looks as if you assume there is nothing except the bitset in the
>message but that is not true. Even with your proposed breaking of
>current groups, you would still have e.g. 4 bitsets in reply to netdev
>features query, 3 in timestamping info GET request and often bitsets
>combined with other data (e.g. WoL modes and optional WoL password).
>If you wanted to further refine the message granularity to the level of
>single parameters, we might be out of message type ids already.
You can still have multiple bitsets(bitfields) in single message and
have separate cmd/cmds to get string-bit mapping. No need to mangle it.
>
>Unless you want to forget about structured data completely and turn
>everything into tunables - but that's rather scary idea.
>
>Michal
next prev parent reply other threads:[~2019-07-04 8:04 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-02 11:49 [PATCH net-next v6 00/15] ethtool netlink interface, part 1 Michal Kubecek
2019-07-02 11:49 ` [PATCH net-next v6 01/15] rtnetlink: provide permanent hardware address in RTM_NEWLINK Michal Kubecek
2019-07-02 11:57 ` Jiri Pirko
2019-07-02 14:55 ` Stephen Hemminger
2019-07-02 16:35 ` Michal Kubecek
2019-07-02 11:49 ` [PATCH net-next v6 02/15] netlink: rename nl80211_validate_nested() to nla_validate_nested() Michal Kubecek
2019-07-02 12:03 ` Jiri Pirko
2019-07-02 12:15 ` Johannes Berg
2019-07-02 12:15 ` Johannes Berg
2019-07-02 11:49 ` [PATCH net-next v6 03/15] ethtool: move to its own directory Michal Kubecek
2019-07-02 11:49 ` [PATCH net-next v6 04/15] ethtool: introduce ethtool netlink interface Michal Kubecek
2019-07-02 12:25 ` Jiri Pirko
2019-07-02 14:52 ` Michal Kubecek
2019-07-03 8:41 ` Jiri Pirko
2019-07-08 17:27 ` Michal Kubecek
2019-07-08 18:12 ` Johannes Berg
2019-07-08 19:26 ` Jiri Pirko
2019-07-08 19:28 ` Jiri Pirko
2019-07-08 20:22 ` Michal Kubecek
2019-07-09 13:42 ` Jiri Pirko
2019-07-10 12:12 ` Michal Kubecek
2019-07-03 1:29 ` Jakub Kicinski
2019-07-03 6:35 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 05/15] ethtool: helper functions for " Michal Kubecek
2019-07-02 13:05 ` Jiri Pirko
2019-07-02 16:34 ` Michal Kubecek
2019-07-03 1:28 ` Jakub Kicinski
2019-07-03 10:04 ` Jiri Pirko
2019-07-03 11:13 ` Michal Kubecek
2019-07-08 12:22 ` Michal Kubecek
2019-07-08 14:40 ` Jiri Pirko
2019-07-03 1:37 ` Jakub Kicinski
2019-07-03 7:23 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 06/15] ethtool: netlink bitset handling Michal Kubecek
2019-07-03 11:49 ` Jiri Pirko
2019-07-03 13:44 ` Johannes Berg
2019-07-03 14:37 ` Jiri Pirko
2019-07-04 12:07 ` Johannes Berg
2019-07-03 18:18 ` Michal Kubecek
2019-07-04 8:04 ` Jiri Pirko [this message]
2019-07-04 11:52 ` Michal Kubecek
2019-07-04 12:03 ` Johannes Berg
2019-07-04 12:17 ` Michal Kubecek
2019-07-04 12:21 ` Johannes Berg
2019-07-04 12:53 ` Michal Kubecek
2019-07-04 13:10 ` Johannes Berg
2019-07-04 14:31 ` Andrew Lunn
2019-07-09 14:18 ` Jiri Pirko
2019-07-10 12:38 ` Michal Kubecek
2019-07-10 12:59 ` Jiri Pirko
2019-07-10 14:37 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 07/15] ethtool: support for netlink notifications Michal Kubecek
2019-07-03 13:33 ` Jiri Pirko
2019-07-03 14:16 ` Michal Kubecek
2019-07-04 8:06 ` Jiri Pirko
2019-07-03 13:39 ` Johannes Berg
2019-07-03 14:18 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 08/15] ethtool: move string arrays into common file Michal Kubecek
2019-07-03 13:44 ` Jiri Pirko
2019-07-03 14:37 ` Michal Kubecek
2019-07-04 8:09 ` Jiri Pirko
2019-07-02 11:50 ` [PATCH net-next v6 09/15] ethtool: generic handlers for GET requests Michal Kubecek
2019-07-03 14:25 ` Jiri Pirko
2019-07-03 17:53 ` Michal Kubecek
2019-07-04 8:45 ` Jiri Pirko
2019-07-04 8:49 ` Jiri Pirko
2019-07-04 9:28 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 10/15] ethtool: provide string sets with STRSET_GET request Michal Kubecek
2019-07-04 8:17 ` Jiri Pirko
2019-07-02 11:50 ` [PATCH net-next v6 11/15] ethtool: provide link mode names as a string set Michal Kubecek
2019-07-03 2:04 ` Jakub Kicinski
2019-07-03 2:11 ` Jakub Kicinski
2019-07-03 7:38 ` Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 12/15] ethtool: provide link settings and link modes in SETTINGS_GET request Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 13/15] ethtool: add standard notification handler Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 14/15] ethtool: set link settings and link modes with SETTINGS_SET request Michal Kubecek
2019-07-02 11:50 ` [PATCH net-next v6 15/15] ethtool: provide link state in SETTINGS_GET request Michal Kubecek
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