Re: [PATCH 0/4] tracing: improve symbolic printing

On Thu, 21 Sep 2023 10:51:30 +0200 Johannes Berg wrote:

So I was frustrated with not seeing the names of SKB dropreasons
for all but the core reasons, and then while looking into this
all, realized, that the current __print_symbolic() is pretty bad
anyway.

So I came up with a new approach, using a separate declaration
of the symbols, and __print_sym() in there, but to userspace it
all doesn't matter, it shows it the same way, just dyamically
instead of munging with the strings all the time.

This is a huge .data savings as far as I can tell, with a modest
amount (~4k) of .text addition, while making it all dynamic and
in the SKB dropreason case even reusing the existing list that
dropmonitor uses today. Surely patch 3 isn't needed here, but it
felt right.

Anyway, I think it's a pretty reasonable approach overall, and
it does works.

I've listed a number of open questions in the first patch since
that's where the real changes for this are.

Potentially naive question - the trace point holds enum skb_drop_reason.
The user space can get the names from BTF. Can we not teach user space
to generically look up names of enums in BTF?