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If the CPU bandwidth capacity permits, it may be useful to mirror the entire ingress of a user port to software. This is in fact possible to express even if there is no net_device representation for the CPU port. In fact, that approach was already exhausted and that representation wouldn't have even helped [1]. The idea behind implementing this is that currently, we refuse to offload any mirroring towards a non-DSA target net_device. But if we acknowledge the fact that to reach any foreign net_device, the switch must send the packet to the CPU anyway, then we can simply offload just that part, and let the software do the rest. There is only one condition we need to uphold: the filter needs to be present in the software data path as well (no skip_sw). There are 2 actions to consider: FLOW_ACTION_MIRRED (redirect to egress of target interface) and FLOW_ACTION_MIRRED_INGRESS (redirect to ingress of target interface). We don't have the ability/API to offload FLOW_ACTION_MIRRED_INGRESS when the target port is also a DSA user port, but we could also permit that through mirred to the CPU + software. Example: $ ip link add dummy0 type dummy; ip link set dummy0 up $ tc qdisc add dev swp0 clsact $ tc filter add dev swp0 ingress matchall action mirred ingress mirror dev dummy0 Any DSA driver with a ds->ops->port_mirror_add() implementation can now make use of this with no additional change. [1] https://lore.kernel.org/netdev/20191002233750.13566-1-olteanv@gmail.com/ Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Link: https://patch.msgid.link/20241023135251.1752488-6-vladimir.oltean@nxp.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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 reStructuredText 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.