netdev - Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

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Message-ID: <20201105085818.4f20f3ed@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 5 Nov 2020 08:58:18 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com, daniel@...earbox.net,
        kernel-team@...com, Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module
 BTFs

On Thu, 5 Nov 2020 17:46:16 +0100 Greg Kroah-Hartman wrote:
> On Thu, Nov 05, 2020 at 08:39:25AM -0800, Jakub Kicinski wrote:
> > On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:  
> > > Add kernel module listener that will load/validate and unload module BTF.
> > > Module BTFs gets ID generated for them, which makes it possible to iterate
> > > them with existing BTF iteration API. They are given their respective module's
> > > names, which will get reported through GET_OBJ_INFO API. They are also marked
> > > as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> > > 
> > > Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> > > sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> > > tools to inspect module BTF contents and dump their types with existing tools:  
> > 
> > Is there any precedent for creating per-module files under a new
> > sysfs directory structure? My intuition would be that these files 
> > belong under /sys/module/  
> 
> Ick, why?  What's wrong with them under btf?  The module core code
> "owns" the /sys/modules/ tree.  If you want others to mess with that, 
> it will get tricky.

It's debug info, that's where I would look for it. 

Clearly I'd be wrong to do so :)