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![Vladimir Oltean](/assets/img/avatar_default.png)
We collect the software statistics counters for RX bytes (reported to /proc/net/dev and to ethtool -S $dev | grep 'rx_bytes: ") at a time when skb->len has already been adjusted by the eth_type_trans() -> skb_pull_inline(skb, ETH_HLEN) call to exclude the L2 header. This means that when connecting 2 DSA interfaces back to back and sending 1 packet with length 100, the sending interface will report tx_bytes as incrementing by 100, and the receiving interface will report rx_bytes as incrementing by 86. Since accounting for that in scripts is quirky and is something that would be DSA-specific behavior (requiring users to know that they are running on a DSA interface in the first place), the proposal is that we treat it as a bug and fix it. This design bug has always existed in DSA, according to my analysis: commit91da11f870
("net: Distributed Switch Architecture protocol support") also updates skb->dev->stats.rx_bytes += skb->len after the eth_type_trans() call. Technically, prior to Florian's commita86d8becc3
("net: dsa: Factor bottom tag receive functions"), each and every vendor-specific tagging protocol driver open-coded the same bug, until the buggy code was consolidated into something resembling what can be seen now. So each and every driver should have its own Fixes: tag, because of their different histories until the convergence point. I'm not going to do that, for the sake of simplicity, but just blame the oldest appearance of buggy code. There are 2 ways to fix the problem. One is the obvious way, and the other is how I ended up doing it. Obvious would have been to move dev_sw_netstats_rx_add() one line above eth_type_trans(), and below skb_push(skb, ETH_HLEN). But DSA processing is not as simple as that. We count the bytes after removing everything DSA-related from the packet, to emulate what the packet's length was, on the wire, when the user port received it. When eth_type_trans() executes, dsa_untag_bridge_pvid() has not run yet, so in case the switch driver requests this behavior - commit412a1526d0
("net: dsa: untag the bridge pvid from rx skbs") has the details - the obvious variant of the fix wouldn't have worked, because the positioning there would have also counted the not-yet-stripped VLAN header length, something which is absent from the packet as seen on the wire (there it may be untagged, whereas software will see it as PVID-tagged). Fixes:f613ed665b
("net: dsa: Add support for 64-bit statistics") Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
243 lines
5.6 KiB
C
243 lines
5.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* DSA tagging protocol handling
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*
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* Copyright (c) 2008-2009 Marvell Semiconductor
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* Copyright (c) 2013 Florian Fainelli <florian@openwrt.org>
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* Copyright (c) 2016 Andrew Lunn <andrew@lunn.ch>
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*/
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#include <linux/netdevice.h>
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#include <linux/ptp_classify.h>
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#include <linux/skbuff.h>
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#include <net/dsa.h>
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#include <net/dst_metadata.h>
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#include "slave.h"
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#include "tag.h"
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static LIST_HEAD(dsa_tag_drivers_list);
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static DEFINE_MUTEX(dsa_tag_drivers_lock);
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/* Determine if we should defer delivery of skb until we have a rx timestamp.
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*
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* Called from dsa_switch_rcv. For now, this will only work if tagging is
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* enabled on the switch. Normally the MAC driver would retrieve the hardware
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* timestamp when it reads the packet out of the hardware. However in a DSA
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* switch, the DSA driver owning the interface to which the packet is
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* delivered is never notified unless we do so here.
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*/
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static bool dsa_skb_defer_rx_timestamp(struct dsa_slave_priv *p,
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struct sk_buff *skb)
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{
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struct dsa_switch *ds = p->dp->ds;
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unsigned int type;
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if (!ds->ops->port_rxtstamp)
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return false;
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if (skb_headroom(skb) < ETH_HLEN)
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return false;
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__skb_push(skb, ETH_HLEN);
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type = ptp_classify_raw(skb);
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__skb_pull(skb, ETH_HLEN);
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if (type == PTP_CLASS_NONE)
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return false;
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return ds->ops->port_rxtstamp(ds, p->dp->index, skb, type);
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}
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static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
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struct packet_type *pt, struct net_device *unused)
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{
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struct metadata_dst *md_dst = skb_metadata_dst(skb);
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struct dsa_port *cpu_dp = dev->dsa_ptr;
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struct sk_buff *nskb = NULL;
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struct dsa_slave_priv *p;
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if (unlikely(!cpu_dp)) {
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kfree_skb(skb);
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return 0;
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}
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skb = skb_unshare(skb, GFP_ATOMIC);
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if (!skb)
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return 0;
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if (md_dst && md_dst->type == METADATA_HW_PORT_MUX) {
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unsigned int port = md_dst->u.port_info.port_id;
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skb_dst_drop(skb);
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if (!skb_has_extensions(skb))
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skb->slow_gro = 0;
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skb->dev = dsa_master_find_slave(dev, 0, port);
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if (likely(skb->dev)) {
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dsa_default_offload_fwd_mark(skb);
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nskb = skb;
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}
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} else {
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nskb = cpu_dp->rcv(skb, dev);
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}
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if (!nskb) {
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kfree_skb(skb);
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return 0;
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}
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skb = nskb;
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skb_push(skb, ETH_HLEN);
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skb->pkt_type = PACKET_HOST;
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skb->protocol = eth_type_trans(skb, skb->dev);
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if (unlikely(!dsa_slave_dev_check(skb->dev))) {
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/* Packet is to be injected directly on an upper
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* device, e.g. a team/bond, so skip all DSA-port
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* specific actions.
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*/
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netif_rx(skb);
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return 0;
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}
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p = netdev_priv(skb->dev);
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if (unlikely(cpu_dp->ds->untag_bridge_pvid)) {
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nskb = dsa_untag_bridge_pvid(skb);
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if (!nskb) {
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kfree_skb(skb);
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return 0;
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}
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skb = nskb;
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}
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dev_sw_netstats_rx_add(skb->dev, skb->len + ETH_HLEN);
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if (dsa_skb_defer_rx_timestamp(p, skb))
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return 0;
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gro_cells_receive(&p->gcells, skb);
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return 0;
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}
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struct packet_type dsa_pack_type __read_mostly = {
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.type = cpu_to_be16(ETH_P_XDSA),
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.func = dsa_switch_rcv,
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};
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static void dsa_tag_driver_register(struct dsa_tag_driver *dsa_tag_driver,
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struct module *owner)
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{
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dsa_tag_driver->owner = owner;
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mutex_lock(&dsa_tag_drivers_lock);
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list_add_tail(&dsa_tag_driver->list, &dsa_tag_drivers_list);
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mutex_unlock(&dsa_tag_drivers_lock);
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}
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void dsa_tag_drivers_register(struct dsa_tag_driver *dsa_tag_driver_array[],
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unsigned int count, struct module *owner)
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{
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unsigned int i;
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for (i = 0; i < count; i++)
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dsa_tag_driver_register(dsa_tag_driver_array[i], owner);
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}
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static void dsa_tag_driver_unregister(struct dsa_tag_driver *dsa_tag_driver)
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{
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mutex_lock(&dsa_tag_drivers_lock);
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list_del(&dsa_tag_driver->list);
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mutex_unlock(&dsa_tag_drivers_lock);
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}
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EXPORT_SYMBOL_GPL(dsa_tag_drivers_register);
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void dsa_tag_drivers_unregister(struct dsa_tag_driver *dsa_tag_driver_array[],
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unsigned int count)
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{
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unsigned int i;
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for (i = 0; i < count; i++)
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dsa_tag_driver_unregister(dsa_tag_driver_array[i]);
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}
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EXPORT_SYMBOL_GPL(dsa_tag_drivers_unregister);
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const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops)
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{
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return ops->name;
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};
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/* Function takes a reference on the module owning the tagger,
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* so dsa_tag_driver_put must be called afterwards.
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*/
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const struct dsa_device_ops *dsa_tag_driver_get_by_name(const char *name)
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{
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const struct dsa_device_ops *ops = ERR_PTR(-ENOPROTOOPT);
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struct dsa_tag_driver *dsa_tag_driver;
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request_module("%s%s", DSA_TAG_DRIVER_ALIAS, name);
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mutex_lock(&dsa_tag_drivers_lock);
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list_for_each_entry(dsa_tag_driver, &dsa_tag_drivers_list, list) {
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const struct dsa_device_ops *tmp = dsa_tag_driver->ops;
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if (strcmp(name, tmp->name))
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continue;
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if (!try_module_get(dsa_tag_driver->owner))
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break;
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ops = tmp;
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break;
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}
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mutex_unlock(&dsa_tag_drivers_lock);
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return ops;
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}
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const struct dsa_device_ops *dsa_tag_driver_get_by_id(int tag_protocol)
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{
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struct dsa_tag_driver *dsa_tag_driver;
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const struct dsa_device_ops *ops;
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bool found = false;
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request_module("%sid-%d", DSA_TAG_DRIVER_ALIAS, tag_protocol);
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mutex_lock(&dsa_tag_drivers_lock);
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list_for_each_entry(dsa_tag_driver, &dsa_tag_drivers_list, list) {
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ops = dsa_tag_driver->ops;
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if (ops->proto == tag_protocol) {
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found = true;
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break;
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}
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}
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if (found) {
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if (!try_module_get(dsa_tag_driver->owner))
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ops = ERR_PTR(-ENOPROTOOPT);
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} else {
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ops = ERR_PTR(-ENOPROTOOPT);
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}
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mutex_unlock(&dsa_tag_drivers_lock);
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return ops;
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}
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void dsa_tag_driver_put(const struct dsa_device_ops *ops)
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{
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struct dsa_tag_driver *dsa_tag_driver;
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mutex_lock(&dsa_tag_drivers_lock);
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list_for_each_entry(dsa_tag_driver, &dsa_tag_drivers_list, list) {
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if (dsa_tag_driver->ops == ops) {
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module_put(dsa_tag_driver->owner);
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break;
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}
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}
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mutex_unlock(&dsa_tag_drivers_lock);
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}
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