[PATCH 15/16] dyndbg: allow inverted-flag-chars in modflags

[Jim Cromie <jim.cromie@gmail.com>]

Extend flags modifications to allow [PFMLT_XYZ] inverted flags.
This allows control-queries like:

  #> Q () { echo file inode.c $* > control } # to type less
  #> Q -P	# same as +p
  #> Q +X	# same as -x
  #> Q xyz-P	# same as xyz+p

This allows flags in a callsite to be simultaneously set and cleared,
while still starting with the current flagstate (with +- ops).
Generally, you chose -p or +p 1st, then set or clear flags
accordingly.

  # enable print on callsites with 'xy'; and re-mark with just 'z'
  #> Q xy+pXYz

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 Documentation/admin-guide/dynamic-debug-howto.rst | 8 +++++---
 lib/dynamic_debug.c                               | 6 ++++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 5404e23eeac8..493e74a14bdd 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -250,9 +250,11 @@ only callsites with x&y cleared.
 
 Flagsets cannot contain ``xX`` etc, a flag cannot be true and false.
 
-modflags containing upper-case flags is reserved/undefined for now.
-inverted-flags are currently ignored, usage gets trickier if given
-``-pXy``, it should leave x set.
+modflags may contain upper-case flags also, using these lets you
+invert the flag setting implied by the OP; '-pX' means disable
+printing, and mark that callsite with usr-x flag to create a group,
+for optional further manipulation.  Generally, '+p' and '-p' is your
+main choice, and use of inverted flags in modflags is rare.
 
 Notes::
 
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b2630df0c3a5..82daf95b8f64 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -488,15 +488,17 @@ static int ddebug_parse_flags(const char *str,
 
 	/* calculate final mods: flags, mask based upon op */
 	switch (op) {
+		unsigned int tmp;
 	case '=':
 		mods->mask = 0;
 		break;
 	case '+':
-		mods->mask = ~0U;
+		mods->mask = ~mods->mask;
 		break;
 	case '-':
+		tmp = mods->mask;
 		mods->mask = ~mods->flags;
-		mods->flags = 0;
+		mods->flags = tmp;
 		break;
 	}
 
-- 
2.23.0