On Thu, Nov 18, 2021 at 12:50:58PM +0100, Toke Høiland-Jørgensen wrote:
> Paolo Abeni <pabeni@xxxxxxxxxx> writes:
>
> > Hello,
> >
> > On Wed, 2021-11-17 at 16:48 -0800, Alexei Starovoitov wrote:
> >> On Mon, Nov 15, 2021 at 06:09:28PM +0100, Toke Høiland-Jørgensen wrote:
> >> > Paolo Abeni <pabeni@xxxxxxxxxx> writes:
> >> >
> >> > > > > - pr_warn_once("%s XDP return value %u, expect packet loss!\n",
> >> > > > > + pr_warn_once("%s XDP return value %u on prog %d dev %s attach type %d, expect packet loss!\n",
> >> > > > > act > act_max ? "Illegal" : "Driver unsupported",
> >> > > > > - act);
> >> > > > > + act, prog->aux->id, dev->name, prog->expected_attach_type);
> >> > > >
> >> > > > This will only ever trigger once per reboot even if the message differs,
> >> > > > right? Which makes it less useful as a debugging aid; so I'm not sure if
> >> > > > it's really worth it with this intrusive change unless we also do
> >> > > > something to add a proper debugging aid (like a tracepoint)...
> >> > >
> >> > > Yes, the idea would be to add a tracepoint there, if there is general
> >> > > agreement about this change.
> >> > >
> >> > > I think this patch is needed because the WARN_ONCE splat gives
> >> > > implicitly information about the related driver and attach type.
> >> > > Replacing with a simple printk we lose them.
> >> >
> >> > Ah, right, good point. Pointing that out in the commit message might be
> >> > a good idea; otherwise people may miss that ;)
> >>
> >> Though it's quite a churn across the drivers I think extra verbosity here is justified.
> >> I'd only suggest to print stable things. Like prog->aux->id probably has
> >> little value for the person looking at the logs. That prog id is likely gone.
> >> If it was prog->aux->name it would be more helpful.
> >> Same with expected_attach_type. Why print it at all?
> >> tracepoint is probably good idea too.
> >
> > Thanks for the feedback.
> >
> > I tried to select the additional arguments to allow the user/admin
> > tracking down which program is causing the issue and why. I'm a
> > complete newbe wrt XDP, so likely my choice were naive.
> >
> > I thought the id identifies the program in an unambiguous manner. I
> > understand the program could be unloaded meanwhile, but if that is not
> > the case the id should be quite useful. Perhaps we could dump both the
> > id and the name?
> >
> > I included the attach type as different types support/allow different
> > actions: the same program could cause the warning or not depending on
> > it. If that is not useful I can drop the attach type from the next
> > iteration.
>
> The attach type identifies DEVMAP and CPUMAP programs, but just printing
> it as a number probably doesn't make sense. So maybe something like:
>
> switch(prog->expected_attach_type) {
> case BPF_XDP_DEVMAP:
> case BPF_XDP_CPUMAP:
> pr_warn_once("Illegal XDP return value %u from prog %s(%d) in %s!\n",
> act, prog->aux_name, prog->aux->id,
> prog->expected_attach_type == BPF_XDP_DEVMAP ? "devmap" : "cpumap");
> break;
> default:
> pr_warn_once("%s XDP return value %u on prog %s(%d) dev %s, expect packet loss!\n",
> act > act_max ? "Illegal" : "Driver unsupported",
> act, prog->aux->name, prog->aux->id, dev->name);
> break;
imo it's an overkill for a debug message that should not be seen.
Just attach bpf probe to this function and print whatever necessary.
Keep kernel message single line and short that is easily greppable.
