linux-kernel - Re: [PATCH v2 17/24] dyndbg: add user-flag, negating-flags, and filtering on flags

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Date:   Tue, 16 Jun 2020 13:41:56 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Jim Cromie <jim.cromie@...il.com>
Cc:     jbaron@...mai.com, linux-kernel@...r.kernel.org,
        akpm@...uxfoundation.org, gregkh@...uxfoundation.org,
        linux@...musvillemoes.dk, Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Orson Zhai <orson.zhai@...soc.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 17/24] dyndbg: add user-flag, negating-flags, and
 filtering on flags

On Sat 2020-06-13 09:57:31, Jim Cromie wrote:
> 1. Add a user-flag [u] which works like the [pfmlt] flags, but has no
> effect on callsite behavior; it allows incremental marking of
> arbitrary sets of callsites.
> 
> 2. Add [PFMLTU] flags, which negate their counterparts; P===!p etc.
> And in ddebug_read_flags():
>    current code does:	[pfmltu_] -> flags
>    copy it to:		[PFMLTU_] -> mask
> 
> also disallow both of a pair: ie no 'pP', no true & false.
> 
> 3. Add filtering ops into ddebug_change(), right after all the
> callsite-property selections are complete.  These filter on the
> callsite's current flagstate before applying modflags.
> 
> Why ?
> 
> The 'u' flag lets the user assemble an arbitary set of callsites.
> Then using filter flags, user can activate the 'u' set.
> 
>   #> echo 'file foo.c +u; file bar.c +u' > control   # and repeat
>   #> echo 'u+p' > control

What was the motivation for this please?
Is it common to manipulate the same set of callsites again and again?
Do you have any usecase, please?

Best Regards,
Petr