linux-kernel - Re: [re: PATCH v2 00/15 - 08/11] dyndbg: split multi-query strings with %

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Date:   Sun, 10 Dec 2023 18:07:11 -0700
From:   jim.cromie@...il.com
To:     Łukasz Bartosik <lb@...ihalf.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        bleung@...gle.com, contact@...rsion.fr, daniel@...ll.ch,
        dianders@...omium.org, groeck@...gle.com, jbaron@...mai.com,
        john.ogness@...utronix.de, keescook@...omium.org, pmladek@...e.com,
        ppaalanen@...il.com, rostedt@...dmis.org, seanpaul@...omium.org,
        sergey.senozhatsky@...il.com, upstream@...ihalf.com,
        vincent.whitchurch@...s.com, yanivt@...gle.com,
        gregkh@...uxfoundation.org
Subject: Re: [re: PATCH v2 00/15 - 08/11] dyndbg: split multi-query strings
 with %

On Fri, Dec 8, 2023 at 5:32 PM Łukasz Bartosik <lb@...ihalf.com> wrote:
>
> pt., 8 gru 2023 o 01:15 Jim Cromie <jim.cromie@...il.com> napisał(a):
> >

> >   vng -v --user root -p 4 \
> >       -a dynamic_debug.verbose=3 \
> >       -a \*.dyndbg=class,DRM_UT_CORE,+pfmlt_%class,DRM_UT_KMS,+pfm%class,DRM_UT_ATOMIC,+pf
> >
> > ':' would be a more natural multi-cmd separator, but is reserved
> > for +T:<trace_buf> to designate separate tracebuf instances.
> >
> > If '%' is distasteful, the backup plan is ",_,", since that would
> > never appear in a useful <format "$foo"> cmd.
> >
>
> What if we use a different character for passing trace instance name
> to the T flag, for example "-", +T-trace_buf
> and then use ":" instead of "%" as a separator ?
>

*** entering the Bikeshed ***

One of the nice constraints of the flags-val is that it always starts with +/-/=
the 1st char of flags is the only place they would appear unquoted.
using '-' again dilutes that specialness.

the whole +T:named_stream. syntax has a mnemonic value,
it seems to explain itself (but I'm weird)

WRT to ':' vs '%' as multi-cmd separator, what do we lose in each trade ?
ultimately it invalidates a query containing those chars. IOW

  # impossible query when cmd-splitting on %
  echo format "search for %s because %d" +p > /proc/dynamic_debug/control

  # impossible when splitting on :
  echo format "my_label: " +p > /proc/dynamic_debug/control

NB: only format would see an arg with either : or %, since theyre
*never* in filenames, functions or module (or class) names.

Of the 2, % is even more unlikely to wind up in a name,
colon already appears in host:path and urls,
and in some class-name systems
(tho not planned for "class" keyword)

the ability to search for colon-terminated labels seems more useful
than searching for a particular set of printf format specifiers,
which btw cant have colons between them.