linux-kernel - Re: tracing/user_events: Tracking broken status and feedback

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Date:   Thu, 28 Jul 2022 17:02:34 -0700
From:   Beau Belgrave <beaub@...ux.microsoft.com>
To:     rostedt@...dmis.org, mhiramat@...nel.org,
        mathieu.desnoyers@...icios.com
Cc:     linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        beaub@...ux.microsoft.com
Subject: Re: tracing/user_events: Tracking broken status and feedback

On Mon, Jul 25, 2022 at 04:19:00PM -0700, Beau Belgrave wrote:
> To help keep track of what is required to remove the broken status from
> user_events I am starting this thread. I would like to use this thread
> to provide status on the work that has been done so far and to have a
> discussion about when the broken status can be removed.
> 
> Feedback threads from 5.18 version of user_events:
> 1. https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/
> 2. https://lore.kernel.org/all/1651771383.54437.1652370439159.JavaMail.zimbra@efficios.com/
> 
> All the feedback has been addressed in the patchsets 1 and 2 (see below).
> Here are the details: 
> 
> 1. Use bits vs bytes in event enabled memory mappings.
> Fixed in patchset 1.
> 
> 2. Pack ABI structures where size is used.
> Fixed in patchset 1.
> 
> 3. Don't trust user strings for string formatting.
> Fixed in patchset 1.
> 
> 4. Move to refcount APIs vs atomic for tracking references.
> Fixed in patchset 1.
> 
> 5. Ensure event_mutex is held during registration.
> Fixed in patchset 2.
> 
> With these, I believe I have addressed all issues to remove the
> "broken status".
> 
> Here is the list of additional feedback (and status) that I don't believe
> should have a bearing on removing the "broken status":
> 
> 1. Kernel vs user tracers in ABI.
> This is not done, the plan is to build a libtracepoint library that allows
> working with both kernel and user tracers in user programs. Steven is
> working on this at the moment. I don't believe this is required to remove
> the broken status, but it will help prove the ABI by having it.
> 
> No patchset yet.
> 
> 2. Container/namespace isolation of events.
> user_events utilizes tracefs for user facing files in the ABI. I've created
> an RFC patchset showing how if tracefs offered an isolated directory
> structure per-namespace the user_events ABI is unaffected. This is true for
> other ABIs that tracefs hosts, if they would like to integrate. I don't
> believe this is required to remove the broken status, however, it's useful
> to have to see how the ABI is unaffected while we work toward enabling
> isolation within tracing.
> 
> See patchset 3.
> 
> Patchsets:
> 1. https://lore.kernel.org/all/20220425184631.2068-1-beaub@linux.microsoft.com/
> 2. https://lore.kernel.org/all/20220328223225.1992-1-beaub@linux.microsoft.com/
> 3. https://lore.kernel.org/all/20220707215828.2021-1-beaub@linux.microsoft.com/
> 
> Thanks,
> -Beau

Steven had feedback on patchset 1 here:
https://lore.kernel.org/all/20220726180115.69320865@gandalf.local.home/

I've updated patchset 1 and 3 to address this feedback.

Updated patchsets:
1. https://lore.kernel.org/all/20220728233309.1896-1-beaub@linux.microsoft.com/
3. https://lore.kernel.org/all/20220728235241.2249-1-beaub@linux.microsoft.com/

Thanks,
-Beau