linux-kernel - Re: [PATCH 1/2] trace: Export anonymous tracing

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Message-ID: <158310134594.5508.5362429296192213548@skylake-alporthouse-com>
Date:   Sun, 01 Mar 2020 22:22:25 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] trace: Export anonymous tracing

Quoting Steven Rostedt (2020-03-01 18:18:16)
> On Sun,  1 Mar 2020 15:52:47 +0000
> Chris Wilson <chris@...is-wilson.co.uk> wrote:
> 
> > To facilitate construction of per-client event ringbuffers, in
> > particular for a per-client debug and error report log, it would be
> > extremely useful to create an anonymous file that can be handed to
> > userspace so that it can see its and only its events. trace already
> > provides a means of encapsulating the trace ringbuffer into a struct
> > file that can be opened via the tracefs, and so with a couple of minor
> > tweaks can provide the same access via an anonymous inode.
> 
> I'm curious to why we need it to be anonymous. Why not allow them to be
> visible from the tracing directory. This could allow for easier
> debugging. Note, the trace instances have ref counters thus they can't
> be removed if something has a reference to it.

Do you really want a few thousand (or even tens) i915-client-%d? That
does not particularly seem like it adds ease-of-use, and would need to be
restricted to the client [or root]. The intent is for the client to have
a private channel for detailed debug/error reporting of its own calls
into the kernel.
-Chris