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Offloading switch device drivers may be able to collect statistics of the traffic taking place in the HW datapath that pertains to a certain soft netdevice, such as VLAN. Add the necessary infrastructure to allow exposing these statistics to the offloaded netdevice in question. The API was shaped by the following considerations: - Collection of HW statistics is not free: there may be a finite number of counters, and the act of counting may have a performance impact. It is therefore necessary to allow toggling whether HW counting should be done for any particular SW netdevice. - As the drivers are loaded and removed, a particular device may get offloaded and unoffloaded again. At the same time, the statistics values need to stay monotonic (modulo the eventual 64-bit wraparound), increasing only to reflect traffic measured in the device. To that end, the netdevice keeps around a lazily-allocated copy of struct rtnl_link_stats64. Device drivers then contribute to the values kept therein at various points. Even as the driver goes away, the struct stays around to maintain the statistics values. - Different HW devices may be able to count different things. The motivation behind this patch in particular is exposure of HW counters on Nvidia Spectrum switches, where the only practical approach to counting traffic on offloaded soft netdevices currently is to use router interface counters, and count L3 traffic. Correspondingly that is the statistics suite added in this patch. Other devices may be able to measure different kinds of traffic, and for that reason, the APIs are built to allow uniform access to different statistics suites. - Because soft netdevices and offloading drivers are only loosely bound, a netdevice uses a notifier chain to communicate with the drivers. Several new notifiers, NETDEV_OFFLOAD_XSTATS_*, have been added to carry messages to the offloading drivers. - Devices can have various conditions for when a particular counter is available. As the device is configured and reconfigured, the device offload may become or cease being suitable for counter binding. A netdevice can use a notifier type NETDEV_OFFLOAD_XSTATS_REPORT_USED to ping offloading drivers and determine whether anyone currently implements a given statistics suite. This information can then be propagated to user space. When the driver decides to unoffload a netdevice, it can use a newly-added function, netdev_offload_xstats_report_delta(), to record outstanding collected statistics, before destroying the HW counter. This patch adds a helper, call_netdevice_notifiers_info_robust(), for dispatching a notifier with the possibility of unwind when one of the consumers bails. Given the wish to eventually get rid of the global notifier block altogether, this helper only invokes the per-netns notifier block. Signed-off-by: Petr Machata <petrm@nvidia.com> Signed-off-by: Ido Schimmel <idosch@nvidia.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.