[PATCH v4 21/39] dyndbg: split multi-query strings with %

From: Łukasz Bartosik
Date: Sat Feb 10 2024 - 18:55:38 EST

From: Jim Cromie <jim.cromie@xxxxxxxxx>

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

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 " mod:*
[ 38.172011] dyndbg: bad flag-op f, at start of format
[ 38.172487] dyndbg: flags parse failed
[ 38.172839] dyndbg: query 1: "s +p" mod:*
[ 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


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, \

':' 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@xxxxxxxxx>
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 78b06a617918..a6c6392cde3e 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1001,7 +1001,7 @@ 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';