On Wed, 19 Dec 2018 08:36:43 +0100 Jesper Dangaard Brouer <bro...@redhat.com> wrote:
> On Tue, 18 Dec 2018 18:27:06 -0800 > Stephen Hemminger <step...@networkplumber.org> wrote: > > > This is the result of a conversation about monitoring of link > > state changes with BPF. > > If you want to use this from BPF then you are in for a surprise. As > tracepoints BPF cannot read these "__string" constructs, here the netdev > name. I tried a lot of different tricks that didn't work, see [1], > until Alexei explained that it simply isn't supported. > > I instead recommend adding the ifindex to the tracepoint. The__string > and __assign_str is also a performance concern as it does strcpy behind > your back. Can we record the ifindex in the event record and do the decode in the printk? This is not a critical path so don't really care that much. > I have an year old TODO list item about improving this: > ** TODO Make perf-script plugin for ifindex to name translation > SCHEDULED: <2017-11-20 Mon> > > Today, the existing network tracepoints using dev->name is not that > usable by BPF, as BPF cannot identify the interface. Thus IMHO it would > make sense to convert the existing network tracepoints dev->name into > dev->ifindex, and then let perf-script convert this to the interface > name. Either in userspace via if_indextoname(3), or (as ACME pointed > out at the time) we might want to have a lookup table stored together > with perf.data for later inspection (in-case ifindexes changed). > > > [1] > https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/samples/bpf/napi_monitor_kern.c#L34-L130 What about the event enum, can BPF take that? Also want to add net namespace create/destroy events.
