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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Andrew Lunn , linux-kernel@vger.kernel.org Subject: [PATCH] net: mention the convention for .ndo_setup_tc() Date: Fri, 8 May 2026 05:40:51 +0800 Message-ID: <20260507214054.2539790-1-mmyangfl@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit qdisc_offload_dump_helper(), originated from commit 602f3baf2218 ("net_sch: red: Add offload ability to RED qdisc"), is designed to that Whether RED is being offloaded is being determined every time dump action is being called because parent change of this qdisc could change its offload state but doesn't require any RED function to be called. and returning -EOPNOTSUPP (for dump queries) does not mean "I don't have any statistics", but "I don't offload this qdisc anymore". At least two existing drivers did it wrong, so it is worth mentioning. Signed-off-by: David Yang --- include/linux/netdevice.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 744ffa243501..b18a6d917771 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -1223,6 +1223,12 @@ struct netdev_net_notifier { * tx queues stopped. This allows the netdevice to perform queue * management safely. * + * NB: Returning -EOPNOTSUPP for whatever commands means "this qdisc is not + * offloaded (anymore, offloading may have silently stopped)", and the + * offloading flag is cleared. This is especially true for dump queries + * (e.g. TC_*_STATS commands). If the underlying device does not report any + * statistics but is still offloading, return 0 instead. + * * Fiber Channel over Ethernet (FCoE) offload functions. * int (*ndo_fcoe_enable)(struct net_device *dev); * Called when the FCoE protocol stack wants to start using LLD for FCoE -- 2.53.0