Commit 34dd0fec authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Jakub Kicinski
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net: sched: generalize check for no-queue qdisc on TX queue 



The "noqueue" qdisc can either be directly attached, or get default
attached if net_device priv_flags has IFF_NO_QUEUE. In both cases, the
allocated Qdisc structure gets it's enqueue function pointer reset to
NULL by noqueue_init() via noqueue_qdisc_ops.

This is a common case for software virtual net_devices. For these devices
with no-queue, the transmission path in __dev_queue_xmit() will bypass
the qdisc layer. Directly invoking device drivers ndo_start_xmit (via
dev_hard_start_xmit).  In this mode the device driver is not allowed to
ask for packets to be queued (either via returning NETDEV_TX_BUSY or
stopping the TXQ).

The simplest and most reliable way to identify this no-queue case is by
checking if enqueue == NULL.

The vrf driver currently open-codes this check (!qdisc->enqueue). While
functionally correct, this low-level detail is better encapsulated in a
dedicated helper for clarity and long-term maintainability.

To make this behavior more explicit and reusable, this patch introduce a
new helper: qdisc_txq_has_no_queue(). Helper will also be used by the
veth driver in the next patch, which introduces optional qdisc-based
backpressure.

This is a non-functional change.

Reviewed-by: default avatarDavid Ahern <dsahern@kernel.org>
Reviewed-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: default avatarJesper Dangaard Brouer <hawk@kernel.org>
Link: https://patch.msgid.link/174559293172.827981.7583862632045264175.stgit@firesoul


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ccc25158

drivers/net/vrf.c

+1 −3
Original line number Diff line number Diff line
@@ -343,15 +343,13 @@ static int vrf_ifindex_lookup_by_table_id(struct net *net, u32 table_id) 
static bool qdisc_tx_is_default(const struct net_device *dev)

{

	struct netdev_queue *txq;

	struct Qdisc *qdisc;



	if (dev->num_tx_queues > 1)

		return false;



	txq = netdev_get_tx_queue(dev, 0);

	qdisc = rcu_access_pointer(txq->qdisc);



	return !qdisc->enqueue;

	return qdisc_txq_has_no_queue(txq);

}



/* Local traffic destined to local address. Reinsert the packet to rx

include/net/sch_generic.h

+8 −0
Original line number Diff line number Diff line
@@ -803,6 +803,14 @@ static inline bool qdisc_tx_changing(const struct net_device *dev) 
	return false;

}



/* "noqueue" qdisc identified by not having any enqueue, see noqueue_init() */

static inline bool qdisc_txq_has_no_queue(const struct netdev_queue *txq)

{

	struct Qdisc *qdisc = rcu_access_pointer(txq->qdisc);



	return qdisc->enqueue == NULL;

}



/* Is the device using the noop qdisc on all queues?  */

static inline bool qdisc_tx_is_noop(const struct net_device *dev)

{