diff mbox

[re:,v2,00/15,-,08/11] dyndbg: split multi-query strings with %

Message ID 5351f56289add68eee2aa5288f82a313c2b9f664.1701993656.git.jim.cromie@gmail.com
State New
Headers

Commit Message

Jim Cromie Dec. 8, 2023, 12:15 a.m. UTC 
  Multi-query strings have long allowed:

  modprobe drm dyndbg="class DRM_UT_CORE +p; class DRM_UT_KMS +p"
  modprobe drm dyndbg=<<EOX
     class DRM_UT_CORE +pmf
     class DRM_UT_KMS  +pmf
  EOX

More recently, the need for quoting was avoided by treating a comma
like a space/token-terminator:

  modprobe drm dyndbg=class,DRM_UT_CORE,+p\;class,DRM_UT_KMS,+p

But that leaves unfinished business; that semi-colon needs escaping,
and thats not robust to further string interpolation.  In particular,
it fails when passed to vng (virtme-ng).

So this patch adds '%' to the existing ';' and '\n' multi-cmd
separators, which is more shell-friendly, and avoids quoting and
escaping hassles.

  modprobe drm dyndbg=class,DRM_UT_CORE,+p%class,DRM_UT_KMS,+p

NOTE: it does alter/break this (ill conceived) search:

[root@v6 lx]# ddcmd format %s +p
[   38.170998] dyndbg: read 13 bytes from userspace
[   38.171542] dyndbg: query 0: <format > on module: <*>
[   38.172011] dyndbg: bad flag-op f, at start of format
[   38.172487] dyndbg: flags parse failed
[   38.172839] dyndbg: query 1: <s +p> on module: <*>
[   38.173285] dyndbg: expecting pairs of match-spec <value>
[   38.173791] dyndbg: query parse failed
[   38.174141] dyndbg: processed 2 queries, with 0 matches, 2 errs
bash: echo: write error: Invalid argument

In trade for that minor format selection limitation, we get to do:

  vng -v --user root -p 4 \
      -a dynamic_debug.verbose=3 \
      -a drm.debug=0x15 \
      -a i915.dyndbg=class,DRM_UT_CORE,+pfmlt_%class,DRM_UT_KMS,+pfml
  modprobe drm
  modprobe i915

NOTES/TLDR:

In this example, using both drm.debug & drm.dyndbg is mostly for
testing.  Using drm.debug is preferred, because the drivers all
explicitly depend on that input/control-point, so settings there are
propagated to drivers.

But more to the point, drm.dyndbg explicitly limits the query to drm.
In fact, you could pass a module wildcard in the above, and achieve
the same thing:

  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.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Łukasz Bartosik Dec. 9, 2023, 12:32 a.m. UTC | #1 
pt., 8 gru 2023 o 01:15 Jim Cromie <jim.cromie@gmail.com> napisał(a):
>
> Multi-query strings have long allowed:
>
>   modprobe drm dyndbg="class DRM_UT_CORE +p; class DRM_UT_KMS +p"
>   modprobe drm dyndbg=<<EOX
>      class DRM_UT_CORE +pmf
>      class DRM_UT_KMS  +pmf
>   EOX
>
> More recently, the need for quoting was avoided by treating a comma
> like a space/token-terminator:
>
>   modprobe drm dyndbg=class,DRM_UT_CORE,+p\;class,DRM_UT_KMS,+p
>
> But that leaves unfinished business; that semi-colon needs escaping,
> and thats not robust to further string interpolation.  In particular,
> it fails when passed to vng (virtme-ng).
>
> So this patch adds '%' to the existing ';' and '\n' multi-cmd
> separators, which is more shell-friendly, and avoids quoting and
> escaping hassles.
>
>   modprobe drm dyndbg=class,DRM_UT_CORE,+p%class,DRM_UT_KMS,+p
>
> NOTE: it does alter/break this (ill conceived) search:
>
> [root@v6 lx]# ddcmd format %s +p
> [   38.170998] dyndbg: read 13 bytes from userspace
> [   38.171542] dyndbg: query 0: <format > on module: <*>
> [   38.172011] dyndbg: bad flag-op f, at start of format
> [   38.172487] dyndbg: flags parse failed
> [   38.172839] dyndbg: query 1: <s +p> on module: <*>
> [   38.173285] dyndbg: expecting pairs of match-spec <value>
> [   38.173791] dyndbg: query parse failed
> [   38.174141] dyndbg: processed 2 queries, with 0 matches, 2 errs
> bash: echo: write error: Invalid argument
>
> In trade for that minor format selection limitation, we get to do:
>
>   vng -v --user root -p 4 \
>       -a dynamic_debug.verbose=3 \
>       -a drm.debug=0x15 \
>       -a i915.dyndbg=class,DRM_UT_CORE,+pfmlt_%class,DRM_UT_KMS,+pfml
>   modprobe drm
>   modprobe i915
>
> NOTES/TLDR:
>
> In this example, using both drm.debug & drm.dyndbg is mostly for
> testing.  Using drm.debug is preferred, because the drivers all
> explicitly depend on that input/control-point, so settings there are
> propagated to drivers.
>
> But more to the point, drm.dyndbg explicitly limits the query to drm.
> In fact, you could pass a module wildcard in the above, and achieve
> the same thing:
>
>   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 ?



> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> ---
>  lib/dynamic_debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index c974f6e19ca1..0ca3ba9e2032 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -963,7 +963,7 @@ static int ddebug_exec_queries(char *query, const char *modname)
>         int i, errs = 0, exitcode = 0, rc, nfound = 0;
>
>         for (i = 0; query; query = split) {
> -               split = strpbrk(query, ";\n");
> +               split = strpbrk(query, "%;\n");
>                 if (split)
>                         *split++ = '\0';
>
> --
> 2.43.0
>
Jim Cromie Dec. 11, 2023, 1:07 a.m. UTC | #2 
On Fri, Dec 8, 2023 at 5:32 PM Łukasz Bartosik <lb@semihalf.com> wrote:
>
> pt., 8 gru 2023 o 01:15 Jim Cromie <jim.cromie@gmail.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.
diff mbox

Patch

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c974f6e19ca1..0ca3ba9e2032 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -963,7 +963,7 @@  static int ddebug_exec_queries(char *query, const char *modname)
 	int i, errs = 0, exitcode = 0, rc, nfound = 0;
 
 	for (i = 0; query; query = split) {
-		split = strpbrk(query, ";\n");
+		split = strpbrk(query, "%;\n");
 		if (split)
 			*split++ = '\0';