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

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Date:   Thu, 25 Nov 2021 14:51:19 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     "jim.cromie@...il.com" <jim.cromie@...il.com>
CC:     Jason Baron <jbaron@...mai.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Sean Paul <seanpaul@...omium.org>, Sean Paul <sean@...rly.run>,
        "quic_saipraka@...cinc.com" <quic_saipraka@...cinc.com>,
        Catalin Marinas <catalin.marinas@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Will Deacon <will@...nel.org>,
        "maz@...nel.org" <maz@...nel.org>,
        amd-gfx mailing list <amd-gfx@...ts.freedesktop.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "quic_psodagud@...cinc.com" <quic_psodagud@...cinc.com>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it
 - RFC

On Fri, Nov 19, 2021 at 11:46:31PM +0100, jim.cromie@...il.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/