linux-kernel - Re: [PATCH] tracing: Set user

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Message-ID: <20220330133758.712768db@gandalf.local.home>
Date:   Wed, 30 Mar 2022 13:37:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-trace-devel <linux-trace-devel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] tracing: Set user_events to BROKEN

On Wed, 30 Mar 2022 12:54:13 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> ----- On Mar 29, 2022, at 10:25 PM, rostedt rostedt@...dmis.org wrote:
> 
> > From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> > 
> > After being merged, user_events become more visible to a wider audience
> > that have concerns with the current API. It is too late to fix this for
> > this release, but instead of a full revert, just mark it as BROKEN (which
> > prevents it from being selected in make config). Then we can work finding
> > a better API. If that fails, then it will need to be completely reverted.  
> 
> Hi Steven,
> 
> What are the constraints for changing a uapi header after it has been present
> in a kernel release ?
> 
> If we are not ready to commit to an ABI, perhaps it would be safer to ensure
> that include/uapi/linux/user_events.h is not installed with the uapi headers
> until it's ready.
> 

Linus may say otherwise, but from what I understand is that we can not
break a user space application from one release to the next. That means, the
only way to break something is if it is actually using something in binary
form.

I can not think of a situation where a header file is useful if the API
it's used for is not available. Thus do we really need to hide it? What
applications will use a header file that has no interface for it?

I do not see the need to remove the uapi if the API for that structure is
not available yet.

-- Steve