Re: [PATCH] net: tcp_drop adds `reason` parameter for tracing v2

[Jakub Kicinski]

On Wed, 25 Aug 2021 09:20:37 -0700 Eric Dumazet wrote:
> On Wed, Aug 25, 2021 at 9:04 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
> > On Wed, 25 Aug 2021 08:47:46 -0700 Eric Dumazet wrote:  
> > > I'd rather use a string. So that we can more easily identify _why_ the
> > > packet was drop, without looking at the source code
> > > of the exact kernel version to locate line number 1057  
> >
> > Yeah, the line number seems like a particularly bad idea. Hopefully
> > strings won't be problematic, given we can expect most serious users
> > to feed the tracepoints via BPF. enum would be more convenient there,
> > I'd think.
> >  
> > > You can be sure that we will get reports in the future from users of
> > > heavily modified kernels.
> > > Having to download a git tree, or apply semi-private patches is a no go.  
> >
> > I'm slightly surprised by this angle. Are there downstream kernels with
> > heavily modified TCP other than Google's?  
> 
> Not sure why Google is mentioned here ?
> Have you ever received a public report about TCP behavior in a Google kernel ?

That's a rhetorical question quite likely, but to be clear - what 
I meant is that Google is the main contributor to Linux TCP and has 
the expertise to make changes. I don't know of any others hence the
question.

> Over the years, we received hundreds of TCP bug reports on
> netdev@vger, where users claim to use  kernel version 4.19 (or other),
> when in fact they use 4.19.xxx
> It takes in general multiple emails exchange before we get a more
> realistic version number.
> Not to mention distro kernels, or even worse private kernels, which
> are not exactly easy to track for us upstream developers.

Right but for backports values come from original patch, enum or string.

I don't mean to dispute your preference tho, if you want strings,
strings it is.