Hi Eric, Thank you for reviewing my patch. I understand your comments and will be and working on correcting what you pointed out. Best, Izabela On Tue, Jul 7, 2020 at 7:52 PM Eric Dumazet wrote: > > > On 7/7/20 10:15 AM, izabela.bakollari@gmail.com wrote: > > From: Izabela Bakollari > > > > 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 > > --- > > include/uapi/linux/net_dropmon.h | 3 ++ > > net/core/drop_monitor.c | 79 +++++++++++++++++++++++++++++++- > > 2 files changed, 80 insertions(+), 2 deletions(-) > > > > diff --git a/include/uapi/linux/net_dropmon.h > b/include/uapi/linux/net_dropmon.h > > index 67e31f329190..e8e861e03a8a 100644 > > --- a/include/uapi/linux/net_dropmon.h > > +++ b/include/uapi/linux/net_dropmon.h > > @@ -58,6 +58,8 @@ enum { > > NET_DM_CMD_CONFIG_NEW, > > NET_DM_CMD_STATS_GET, > > NET_DM_CMD_STATS_NEW, > > + NET_DM_CMD_START_IFC, > > + NET_DM_CMD_STOP_IFC, > > _NET_DM_CMD_MAX, > > }; > > > > @@ -93,6 +95,7 @@ enum net_dm_attr { > > NET_DM_ATTR_SW_DROPS, /* flag */ > > NET_DM_ATTR_HW_DROPS, /* flag */ > > NET_DM_ATTR_FLOW_ACTION_COOKIE, /* binary */ > > + NET_DM_ATTR_IFNAME, /* string */ > > > > __NET_DM_ATTR_MAX, > > NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1 > > diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c > > index 8e33cec9fc4e..8049bff05abd 100644 > > --- a/net/core/drop_monitor.c > > +++ b/net/core/drop_monitor.c > > @@ -30,6 +30,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -46,6 +47,7 @@ > > */ > > static int trace_state = TRACE_OFF; > > static bool monitor_hw; > > +struct net_device *interface; > > > > /* net_dm_mutex > > * > > @@ -220,9 +222,8 @@ static void trace_drop_common(struct sk_buff *skb, > void *location) > > struct per_cpu_dm_data *data; > > unsigned long flags; > > > > - local_irq_save(flags); > > + spin_lock_irqsave(&data->lock, flags); > > data = this_cpu_ptr(&dm_cpu_data); > > - spin_lock(&data->lock); > > dskb = data->skb; > > > > if (!dskb) > > @@ -255,6 +256,12 @@ static void trace_drop_common(struct sk_buff *skb, > void *location) > > > > out: > > spin_unlock_irqrestore(&data->lock, flags); > > + > > What protects interface from being changed under us by another thread/cpu ? > > > + if (interface && interface != skb->dev) { > > + skb = skb_clone(skb, GFP_ATOMIC); > > + skb->dev = interface; > > + netif_receive_skb(skb); > > + } > > } > > > > static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void > *location) > > @@ -1315,6 +1322,63 @@ 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; > > + > > + nd = dev_get_by_name(net, ifname); > > + > > + if (nd) { > > + interface = nd; > > If interface was already set, you forgot to dev_put() it. > > > + dev_hold(interface); > > Note that dev_get_by_name() already did a dev_hold() > > > + } else { > > + return -ENODEV; > > + } > > + return 0; > > +} > > + > > +static int net_dm_interface_stop(struct net *net, const char *ifname) > > +{ > > + struct net_device *nd; > > + > > + nd = dev_get_by_name(net, ifname); > > + > > + if (nd) { > > > > > + interface = nd; > > > You probably meant : interface = NULL; ? > > > + dev_put(interface); > > and dev_put(nd); > > > > + } else { > > + return -ENODEV; > > + } > > + 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]; > > + int rc; > > + > > + 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: > > + rc = net_dm_interface_start(net, ifname); > > + if (rc) > > + return rc; > > + break; > > + case NET_DM_CMD_STOP_IFC: > > + if (interface) { > > + rc = net_dm_interface_stop(net, interface->ifname); > > + return rc; > > + } else { > > + return -ENODEV; > > + } > > + } > > + > > + return 0; > > +} > > + > > static int net_dm_config_fill(struct sk_buff *msg, struct genl_info > *info) > > { > > void *hdr; > > @@ -1543,6 +1607,7 @@ static const struct nla_policy > net_dm_nl_policy[NET_DM_ATTR_MAX + 1] = { > > [NET_DM_ATTR_QUEUE_LEN] = { .type = NLA_U32 }, > > [NET_DM_ATTR_SW_DROPS] = {. type = NLA_FLAG }, > > [NET_DM_ATTR_HW_DROPS] = {. type = NLA_FLAG }, > > + [NET_DM_ATTR_IFNAME] = {. type = NLA_STRING, .len = IFNAMSIZ }, > > }; > > > > static const struct genl_ops dropmon_ops[] = { > > @@ -1570,6 +1635,16 @@ static const struct genl_ops dropmon_ops[] = { > > .cmd = NET_DM_CMD_STATS_GET, > > .doit = net_dm_cmd_stats_get, > > }, > > + { > > + .cmd = NET_DM_CMD_START_IFC, > > + .validate = GENL_DONT_VALIDATE_STRICT | > GENL_DONT_VALIDATE_DUMP, > > + .doit = net_dm_cmd_ifc_trace, > > + }, > > + { > > + .cmd = NET_DM_CMD_STOP_IFC, > > + .validate = GENL_DONT_VALIDATE_STRICT | > GENL_DONT_VALIDATE_DUMP, > > + .doit = net_dm_cmd_ifc_trace, > > + }, > > }; > > > > static int net_dm_nl_pre_doit(const struct genl_ops *ops, > > >