linux-kernel - Re: [PATCH v2 6/7] tracing/user_events: Use bits vs bytes for enabled status page data

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Message-ID: <20220726201412.7fbd3b1f@rorschach.local.home>
Date:   Tue, 26 Jul 2022 20:14:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
        linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 6/7] tracing/user_events: Use bits vs bytes for
 enabled status page data

On Tue, 26 Jul 2022 17:02:49 -0700
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> > >  /* Limit how long of an event name plus args within the subsystem. */
> > >  #define MAX_EVENT_DESC 512
> > >  #define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
> > >  #define MAX_FIELD_ARRAY_SIZE 1024
> > >  
> > > +#define STATUS_BYTE(bit) ((bit) >> 3)
> > > +#define STATUS_MASK(bit) (1 << ((bit) & 7))
> > > +
> > > +/* Internal bits to keep track of connected probes */
> > > +#define EVENT_STATUS_FTRACE (1 << 0)
> > > +#define EVENT_STATUS_PERF (1 << 1)
> > > +#define EVENT_STATUS_OTHER (1 << 7)  
> > 
> > Did you mean to shift STATUS_OTHER by 7?
> >   
> 
> Yes, it should be the value 128.
> 
> > Is EVENT_STATUS_OTHER suppose to be one of the flags within the 3 bits of
> > the 7 in STATUS_MASK?
> >   
> 
> My thought was that STATUS_OTHER would stay on the highest bit.
> Then when we have other systems they would slot into (1 << 2), etc.
> 
> This may not be as important now since the byte is never given back to
> the user and is only used when printing out status via the
> user_events_status file in text form.

So, it is confusing because of STATUS_MASK() is bits 0,1,2 and we are
only using bits 0 and 1, with a OTHER bit at bit 7. And it would be
good to use the BIT() macro.

Is STATUS_OTHER suppose to be part of STATUS_MASK()?

-- Steve