Messages in this thread Patch in this message | | | Subject | Re: [PATCHv2 net-next] dropwatch: Support monitoring of dropped frames | From | Michal Schmidt <> | Date | Mon, 31 Aug 2020 15:18:16 +0200 |
| |
Dne 04. 08. 20 v 18:09 izabela.bakollari@gmail.com napsala: > From: Izabela Bakollari <izabela.bakollari@gmail.com> > > Dropwatch is a utility that monitors dropped frames by having userspace > record them over the dropwatch protocol over a file. This augument > allows live monitoring of dropped frames using tools like tcpdump. > > With this feature, dropwatch allows two additional commands (start and > stop interface) which allows the assignment of a net_device to the > dropwatch protocol. When assinged, dropwatch will clone dropped frames, > and receive them on the assigned interface, allowing tools like tcpdump > to monitor for them. > > With this feature, create a dummy ethernet interface (ip link add dev > dummy0 type dummy), assign it to the dropwatch kernel subsystem, by using > these new commands, and then monitor dropped frames in real time by > running tcpdump -i dummy0. > > Signed-off-by: Izabela Bakollari <izabela.bakollari@gmail.com> > --- > Changes in v2: > - protect the dummy ethernet interface from being changed by another > thread/cpu > --- > include/uapi/linux/net_dropmon.h | 3 ++ > net/core/drop_monitor.c | 84 ++++++++++++++++++++++++++++++++ > 2 files changed, 87 insertions(+) [...] > @@ -255,6 +259,21 @@ static void trace_drop_common(struct sk_buff *skb, void *location) > > out: > spin_unlock_irqrestore(&data->lock, flags); > + spin_lock_irqsave(&interface_lock, flags); > + if (interface && interface != skb->dev) { > + skb = skb_clone(skb, GFP_ATOMIC);
I suggest naming the cloned skb "nskb". Less potential for confusion that way.
> + if (skb) { > + skb->dev = interface; > + spin_unlock_irqrestore(&interface_lock, flags); > + netif_receive_skb(skb); > + } else { > + spin_unlock_irqrestore(&interface_lock, flags); > + pr_err("dropwatch: Not enough memory to clone dropped skb\n");
Maybe avoid logging the error here. In NET_DM_ALERT_MODE_PACKET mode, drop monitor does not log about the skb_clone() failure either. We don't want to open the possibility to flood the logs in case this somehow gets triggered by every packet.
A coding style suggestion - can you rearrange it so that the error path code is spelled out first? Then the regular path does not have to be indented further:
nskb = skb_clone(skb, GFP_ATOMIC); if (!nskb) { spin_unlock_irqrestore(&interface_lock, flags); return; }
/* ... implicit else ... Proceed normally ... */
> + return; > + } > + } else { > + spin_unlock_irqrestore(&interface_lock, flags); > + } > } > > static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location) > @@ -1315,6 +1334,53 @@ static int net_dm_cmd_trace(struct sk_buff *skb, > return -EOPNOTSUPP; > } > > +static int net_dm_interface_start(struct net *net, const char *ifname) > +{ > + struct net_device *nd = dev_get_by_name(net, ifname); > + > + if (nd) > + interface = nd; > + else > + return -ENODEV; > + > + return 0;
Similarly here, consider:
if (!nd) return -ENODEV;
interface = nd; return 0; But maybe I'm nitpicking ...
> +} > + > +static int net_dm_interface_stop(struct net *net, const char *ifname) > +{ > + dev_put(interface); > + interface = NULL; > + > + return 0; > +} > + > +static int net_dm_cmd_ifc_trace(struct sk_buff *skb, struct genl_info *info) > +{ > + struct net *net = sock_net(skb->sk); > + char ifname[IFNAMSIZ]; > + > + if (net_dm_is_monitoring()) > + return -EBUSY; > + > + memset(ifname, 0, IFNAMSIZ); > + nla_strlcpy(ifname, info->attrs[NET_DM_ATTR_IFNAME], IFNAMSIZ - 1); > + > + switch (info->genlhdr->cmd) { > + case NET_DM_CMD_START_IFC: > + if (!interface) > + return net_dm_interface_start(net, ifname); > + else > + return -EBUSY; > + case NET_DM_CMD_STOP_IFC: > + if (interface) > + return net_dm_interface_stop(net, interface->name); > + else > + return -ENODEV;
... and here too.
Best regards, Michal
| |