Mon, Jul 08, 2019 at 10:22:19PM CEST, mkube...@suse.cz wrote: >On Mon, Jul 08, 2019 at 09:26:29PM +0200, Jiri Pirko wrote: >> Mon, Jul 08, 2019 at 07:27:29PM CEST, mkube...@suse.cz wrote: >> > >> >There are two reasons for this design. First is to reduce the number of >> >requests needed to get the information. This is not so much a problem of >> >ethtool itself; the only existing commands that would result in multiple >> >request messages would be "ethtool <dev>" and "ethtool -s <dev>". Maybe >> >also "ethtool -x/-X <dev>" but even if the indirection table and hash >> >key have different bits assigned now, they don't have to be split even >> >if we split other commands. It may be bigger problem for daemons wanting >> >to keep track of system configuration which would have to issue many >> >requests whenever a new device appears. >> > >> >Second reason is that with 8-bit genetlink command/message id, the space >> >is not as infinite as it might seem. I counted quickly, right now the >> >full series uses 14 ids for kernel messages, with split you propose it >> >would most likely grow to 44. For full implementation of all ethtool >> >functionality, we could get to ~60 ids. It's still only 1/4 of the >> >available space but it's not clear what the future development will look >> >like. We would certainly need to be careful not to start allocating new >> >commands for single parameters and try to be foreseeing about what can >> >be grouped together. But we will need to do that in any case. >> > >> >On kernel side, splitting existing messages would make some things a bit >> >easier. It would also reduce the number of scenarios where only part of >> >requested information is available or only part of a SET request fails. >> >> Okay, I got your point. So why don't we look at if from the other angle. >> Why don't we have only single get/set command that would be in general >> used to get/set ALL info from/to the kernel. Where we can have these >> bits (perhaps rather varlen bitfield) to for user to indicate which data >> is he interested in? This scales. The other commands would be >> just for action. >> >> Something like RTM_GETLINK/RTM_SETLINK. Makes sense? > >It's certainly an option but at the first glance it seems as just moving >what I tried to avoid one level lower. It would work around the u8 issue >(but as Johannes pointed out, we can handle it with genetlink when/if >the time comes). We would almost certainly have to split the replies >into multiple messages to keep the packet size reasonable. I'll have to >think more about the consequences for both kernel and userspace. > >My gut feeling is that out of the two extreme options (one universal >message type and message types corresponding to current infomask bits), >the latter is more appealing. After all, ethtool has been gathering >features that would need those ~60 message types for 20 years.
Yeah, but I think that we have to do one or another. Anything in between makes the code complex and uapi confusing. Let's start clean :)
