Messages in this thread | | | Date | Tue, 9 Jul 2019 16:18:17 +0200 | From | Jiri Pirko <> | Subject | Re: [PATCH net-next v6 06/15] ethtool: netlink bitset handling |
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Thu, Jul 04, 2019 at 01:52:36PM CEST, mkubecek@suse.cz wrote: >On Thu, Jul 04, 2019 at 10:04:35AM +0200, Jiri Pirko wrote: >> 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: >> >> >+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. > >There is still the question if it it should be implemented as a nested >attribute which could look like the current compact form without the >"list" flag (if there is no mask, it's a list). Or an unstructured data >block consisting of u32 bit length and one or two bitmaps of >corresponding length. I would prefer the nested attribute, netlink was >designed to represent structured data, passing structures as binary goes >against the design (just looked at VFINFO in rtnetlink few days ago, >it's awful, IMHO). > >Either way, I would still prefer to have bitmaps represented as an array >of 32-bit blocks in host byte order. This would be easy to handle in >kernel both in places where we have u32 based bitmaps and unsigned long >based ones. Other options seem less appealing: > > - u8 based: only complicates processing > - u64 based: have to care about alignment > - unsigned long based: alignment and also problems with 64-bit kernel > vs. 32-bit userspace > >> >> 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. > >Let's take a look at what it means in practice, the command is > > ethtool --set-prif-flags eth3 legacy-rx on > >on an ixgbe card. Currently, ethtool (from the github repository) does > >------------------------------------------------------------------------ >ETHTOOL_CMD_SETTINGS_SET (K->U, 68 bytes) > ETHTOOL_A_HEADER > ETHTOOL_A_DEV_NAME = "eth3" > ETHTOOL_A_SETTINGS_PRIV_FLAGS > ETHTOOL_A_BITSET_BITS > ETHTOOL_A_BITS_BIT > ETHTOOL_A_BIT_NAME = "legacy-rx" > ETHTOOL_A_BIT_VALUE > >NLMSG_ERR (K->U, 36 bytes) err = 0 >------------------------------------------------------------------------ > >If we had only compact form (or some of the NLA_BITFIELD solutions we >are talking about), you would need > >------------------------------------------------------------------------ >ETHTOOL_CMD_STRSET_GET (U->K, 52 bytes) > ETHTOOL_A_HEADER > ETHTOOL_A_DEV_NAME = "eth3" > ETHTOOL_A_STRSET_STRINGSETS > ETHTOOL_A_STRINGSETS_STRINGSET > ETHTOOL_A_STRINGSET_ID = 2 (ETH_SS_PRIV_FLAGS) > >ETHTOOL_CMD_STRSET_GET_REPLY (K->U, 128 bytes) > ETHTOOL_A_HEADER > ETHTOOL_A_DEV_INDEX = 9 > ETHTOOL_A_DEV_NAME = "eth3" > ETHTOOL_A_STRSET_STRINGSETS > ETHTOOL_A_STRINGSETS_STRINGSET > ETHTOOL_A_STRINGSET_ID = 2 (ETH_SS_PRIV_FLAGS) > ETHTOOL_A_STRINGSET_COUNT = 2 > ETHTOOL_A_STRINGSET_STRINGS > ETHTOOL_A_STRINGS_STRING > ETHTOOL_A_STRING_INDEX = 0 > ETHTOOL_A_STRING_VALUE = "legacy-rx" > ETHTOOL_A_STRINGS_STRING > ETHTOOL_A_STRING_INDEX = 1 > ETHTOOL_A_STRING_VALUE = "vf-ipsec" > >NLMSG_ERR (K->U, 36 bytes) err = 0 > >ETHTOOL_CMD_SETTINGS_SET (K->U, 64 bytes) > ETHTOOL_A_HEADER > ETHTOOL_A_DEV_NAME = "eth3" > ETHTOOL_A_SETTINGS_PRIV_FLAGS > ETHTOOL_A_BITSET_SIZE = 2 > ETHTOOL_A_BITSET_VALUE = 00000001 > ETHTOOL_A_BITSET_MASK = 00000001 > >NLMSG_ERR (K->U, 36 bytes) err = 0 >------------------------------------------------------------------------ > >That's an extra roundtrip, lot more chat and the SETTINGS_SET message is >only 4 bytes shorter in the end. And we can consider ourselves lucky >this NIC has only two private flags. Or that we didn't need to enable or >disable a netdev feature (56 bits) or link mode (69 bits and growing). > >We could reduce the overhead by allowing STRSET_GET query to only ask >for specific string(s) but there would still be the extra roundtrip >which I dislike in the ioctl interface. Florian also said in the v5 >discussion that he would like if it was possible to get names and data >together in one request.
I understand. So how about avoid the bitfield all together and just have array of either bits of strings or combinations?
ETHTOOL_CMD_SETTINGS_SET (U->K) ETHTOOL_A_HEADER ETHTOOL_A_DEV_NAME = "eth3" ETHTOOL_A_SETTINGS_PRIV_FLAGS ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_NAME = "legacy-rx" ETHTOOL_A_FLAG_VALUE (NLA_FLAG)
or the same with index instead of string
ETHTOOL_CMD_SETTINGS_SET (U->K) ETHTOOL_A_HEADER ETHTOOL_A_DEV_NAME = "eth3" ETHTOOL_A_SETTINGS_PRIV_FLAGS ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 0 ETHTOOL_A_FLAG_VALUE (NLA_FLAG)
For set you can combine both when you want to set multiple bits:
ETHTOOL_CMD_SETTINGS_SET (U->K) ETHTOOL_A_HEADER ETHTOOL_A_DEV_NAME = "eth3" ETHTOOL_A_SETTINGS_PRIV_FLAGS ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 2 ETHTOOL_A_FLAG_VALUE (NLA_FLAG) ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 8 ETHTOOL_A_FLAG_VALUE (NLA_FLAG) ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_NAME = "legacy-rx" ETHTOOL_A_FLAG_VALUE (NLA_FLAG)
For get this might be a bit bigger message:
ETHTOOL_CMD_SETTINGS_GET_REPLY (K->U) ETHTOOL_A_HEADER ETHTOOL_A_DEV_NAME = "eth3" ETHTOOL_A_SETTINGS_PRIV_FLAGS ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 0 ETHTOOL_A_FLAG_NAME = "legacy-rx" ETHTOOL_A_FLAG_VALUE (NLA_FLAG) ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 1 ETHTOOL_A_FLAG_NAME = "vf-ipsec" ETHTOOL_A_FLAG_VALUE (NLA_FLAG) ETHTOOL_A_SETTINGS_PRIV_FLAG ETHTOOL_A_FLAG_INDEX = 8 ETHTOOL_A_FLAG_NAME = "something-else" ETHTOOL_A_FLAG_VALUE (NLA_FLAG)
> >Michal
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