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: David Ahern <dsahern@xxxxxxxxxx>
Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
---
drivers/net/vrf.c | 4 +---
include/net/sch_generic.h | 8 ++++++++
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 7168b33adadb..9a4beea6ee0c 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -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
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d48c657191cd..b6c177f7141c 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -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)
{
