Re: [PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it - RFC

From: Vincent Whitchurch <vincent.whitchurch@axis.com>
To: "jim.cromie@gmail.com" <jim.cromie@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>,
	Pekka Paalanen <ppaalanen@gmail.com>,
	Sean Paul <seanpaul@chromium.org>, Sean Paul <sean@poorly.run>,
	"quic_saipraka@quicinc.com" <quic_saipraka@quicinc.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Will Deacon <will@kernel.org>, "maz@kernel.org" <maz@kernel.org>,
	amd-gfx mailing list <amd-gfx@lists.freedesktop.org>,
	Ingo Molnar <mingo@redhat.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Arnd Bergmann <arnd@arndb.de>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"intel-gvt-dev@lists.freedesktop.org" 
	<intel-gvt-dev@lists.freedesktop.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"quic_psodagud@quicinc.com" <quic_psodagud@quicinc.com>,
	"mathieu.desnoyers@efficios.com" <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it - RFC
Date: Thu, 25 Nov 2021 14:51:19 +0100	[thread overview]
Message-ID: <20211125135119.GA7625@axis.com> (raw)
In-Reply-To: <CAJfuBxyvDtALAHM53RdnWT4ke6Cjrc3OWTAqNKe_n-o_LhtpYg@mail.gmail.com>

On Fri, Nov 19, 2021 at 11:46:31PM +0100, jim.cromie@gmail.com wrote:
> Vincent's code has the macro magic to define that event, which IIUC
> is what  makes it controllable by ftrace, and therefore acceptable in
> principle to Steve.
> Would there be any reason to expand his set of 2 events into dev_dbg,
> pr_debug etc varieties ?
> (ie any value to separating dev, !dev ?, maybe so
> 
> Sean's code uses trace_array_printk primarily, which is EXPORTed,
> which is a virtue.
> 
> Vincents code does
> +/*
> + * This code is heavily based on __ftrace_trace_stack().
> + *
> + * Allow 4 levels of nesting: normal, softirq, irq, NMI.
> + */
> 
> to implement
> 
> +static void dynamic_trace(const char *fmt, va_list args)
> 
> Has this __ftrace_trace_stack() code been bundled into or hidden under
> a supported interface ?
> 
> would it look anything like trace_array_printk() ?
> 
> what problem is that code solving inside dynamic-debug.c ?

I'm not sure I fully understand all of your questions, but perhaps this
thread with Steven's reply to the first version of my patchset will
answer some of them:

 https://lore.kernel.org/lkml/20200723112644.7759f82f@oasis.local.home/