Re: [RFC PATCH net-next v3 00/21] ethtool netlink interface, part 1

[Florian Fainelli]

Hi Michal,

Let me start with a big thank you for tackling this humongous amount of
work!

On 2/18/2019 10:21 AM, Michal Kubecek wrote:
> Note: this is marked as RFC because it's rather late in the cycle; the plan
> is to make a regular submission (with changes based on review) once
> net-next reopens after the 5.1 merge window. The full (work in progress)
> series, together with the (userspace) ethtool counterpart can be found at
> https://github.com/mkubecek/ethnl
> 
> This is first part of alternative userspace interface for ethtool. The aim
> is to address some long known issues with the ioctl interface, mainly lack
> of extensibility, raciness, limited error reporting and absence of
> notifications.
> 
> The interface uses generic netlink family "ethtool"; it provides multicast
> group "monitor" which is used for notifications. Documentation for the
> interface is in Documentation/networking/ethtool-netlink.txt
> 
> Basic concepts:
> 
> - the goal is to provide all features of ioctl interface but allow
>   easier future extensions; at some point, it should be possible to have
>   full ethtool functionality without using the ioctl interface

+1

> - inextensibility of ioctl interface resulted in way too many commands,
>   many of them obsoleted by newer ones; reduce the number by  ignoring the
>   obsolete commands and grouping some together
> - for "set" type commands, allows passing only the attributes to be
>   changed; therefore we don't need a get-modify-set cycle (which is
>   inherently racy), userspace can simply say what it wants to change
> - provide notifications to multicast group "monitor" like rtnetlink does,
>   i.e. in the form of messages close to replies to "get" requests

+1

> - allow dump requests to get some information about all network devices
>   providing it

And it seems like you have also added some filtering capability with at
least the settings dump, right? That is also highly welcome.

> - be less dependent on ethtool and kernel being in sync; allow e.g. saying
>   "ethtool -s eth0 advertise foo off" without ethtool knowing what "foo"
>   means; it's kernel's job to know what mode "xyz" is and if it exists and
>   is supported
> 
> Main changes between RFC v2 and RFC v3:
> 
> - do not allow building as a module (no netdev notifiers needed)

I would very much prefer that we could build this as a module. Some
systems might be memory constrained or opt to disable ethtool entirely
(security?). If this is not too much trouble, can we try to maintain that?

> - drop some obsolete fields
> - add permanent hw address, timestamping and private flags support
> - rework bitset handling to get rid of variable length arrays
> - notify monitor on device renames
> - restructure GET_SETTINGS/SET_SETTINGS messages
> - split too long patches and submit only first part of the series
> 
> Main changes between RFC v1 and RFC v2:
> 
> - support dumps for all "get" requests
> - provide notifications for changes related to supported request types
> - support getting string sets (both global and per device)
> - support getting/setting device features
> - get rid of family specific header, everything passed as attributes
> - split netlink code into multiple files in net/ethtool/ directory
> 
> ToDo / open questions:
> 
> - some features provided by ethtool would rather belong to devlink (and
>   some are already superseded by devlink); however, only few drivers
>   provide devlink interface at the moment and as recent discussion on
>   flashing revealed, we cannot rely on devlink's presence

Should we just move everything under devlink given that ethtool over
netlink or devlink are essentially manipulating the same (or close to)
objects? It seems to me that at least now is the right time to make
decisions about what should stay in ethtool and be offered via netlink,
what should be migrated to something else (e.g.: Jiri mentioned
rtnetlink), and what is a devlink candidate.

How do we proceed to easily triage which of these netlink facilities
should things be routed to/from?

> 
> - while the netlink interface allows easy future extensions, ethtool_ops
>   interface does not; some settings could be implemented using tunables and
>   accessed via relevant netlink messages (as well as tunables) from
>   userspace but in the long term, something better will be needed

Right, so as a driver writer, one thing I kind of hate is having to fill
a netlink skb myself because that's a lot of work, and it makes it
fairly hard to do mass conversion of internal APIs due to the increased
complexity in auditing what drivers do.

> 
> - currently, all communication with drivers via ethtool_ops is done
>   under RTNL as this is what ioctl interface does and likely many
>   ethtool_ops handlers rely on that; if we are going to rework ethtool_ops
>   in the future ("phase two"), it would be nice to get rid of it
> 
> - ethtool_ops should pass extack pointer to allow drivers more meaningful
>   error reporting; it's not clear, however, how to pass information about
>   offending attribute
> 
> - notifications are sent whenever a change is done via netlink API or
>   ioctl API and for netdev features also whenever they are updated using
>   netdev_change_features(); it would be desirable to notify also about
>   link state and negotiation result (speed/duplex and partner link
>   modes) but it would be more tricky

Historically you listen for a link event and you determine the link
parameters from there, I don't know if there is much value in giving the
full link parameter list, especially given those could theoretically
change depending on your medium (e.g.: wireless), or there could be a
lot to query at that time...

> 
> Michal Kubecek (21):
>   netlink: introduce nla_put_bitfield32()
>   ethtool: move to its own directory
>   ethtool: introduce ethtool netlink interface
>   ethtool: helper functions for netlink interface
>   ethtool: netlink bitset handling
>   ethtool: support for netlink notifications
>   ethtool: implement EVENT notifications
>   ethtool: generic handlers for GET requests
>   ethtool: move string arrays into common file
>   ethtool: provide string sets with GET_STRSET request
>   ethtool: provide driver/device information in GET_INFO request
>   ethtool: provide permanent hardware address in GET_INFO request
>   ethtool: provide timestamping information in GET_INFO request
>   ethtool: provide link mode names as a string set
>   ethtool: provide link settings and link modes in GET_SETTINGS request
>   ethtool: provide WoL information in GET_SETTINGS request
>   ethtool: provide message level in GET_SETTINGS request
>   ethtool: provide link state in GET_SETTINGS request
>   ethtool: provide device features in GET_SETTINGS request
>   ethtool: provide private flags in GET_SETTINGS request
>   ethtool: send netlink notifications about setting changes
> 
>  Documentation/networking/ethtool-netlink.txt | 441 +++++++++++++
>  include/linux/ethtool_netlink.h              |  17 +
>  include/linux/netdevice.h                    |  14 +
>  include/net/netlink.h                        |  15 +
>  include/uapi/linux/ethtool.h                 |  10 +
>  include/uapi/linux/ethtool_netlink.h         | 265 ++++++++
>  include/uapi/linux/net_tstamp.h              |  13 +
>  net/Kconfig                                  |   8 +
>  net/Makefile                                 |   2 +-
>  net/core/Makefile                            |   2 +-
>  net/ethtool/Makefile                         |   7 +
>  net/ethtool/bitset.c                         | 572 +++++++++++++++++
>  net/ethtool/bitset.h                         |  40 ++
>  net/ethtool/common.c                         | 227 +++++++
>  net/ethtool/common.h                         |  29 +
>  net/ethtool/info.c                           | 332 ++++++++++
>  net/{core/ethtool.c => ethtool/ioctl.c}      | 244 ++-----
>  net/ethtool/netlink.c                        | 634 +++++++++++++++++++
>  net/ethtool/netlink.h                        | 252 ++++++++
>  net/ethtool/settings.c                       | 559 ++++++++++++++++
>  net/ethtool/strset.c                         | 461 ++++++++++++++
>  21 files changed, 3937 insertions(+), 207 deletions(-)
>  create mode 100644 Documentation/networking/ethtool-netlink.txt
>  create mode 100644 include/linux/ethtool_netlink.h
>  create mode 100644 include/uapi/linux/ethtool_netlink.h
>  create mode 100644 net/ethtool/Makefile
>  create mode 100644 net/ethtool/bitset.c
>  create mode 100644 net/ethtool/bitset.h
>  create mode 100644 net/ethtool/common.c
>  create mode 100644 net/ethtool/common.h
>  create mode 100644 net/ethtool/info.c
>  rename net/{core/ethtool.c => ethtool/ioctl.c} (91%)
>  create mode 100644 net/ethtool/netlink.c
>  create mode 100644 net/ethtool/netlink.h
>  create mode 100644 net/ethtool/settings.c
>  create mode 100644 net/ethtool/strset.c
> 

-- 
Florian