[PATCH v2 18/24] dyndbg: allow negating flag-chars in modflags

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

Extend flags modifications to allow [PFMLTU] negating flags.
This allows control-queries like:

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

This allows flags in a callsite to be simultaneously set and cleared,
while still starting with the current flagstate (with +- ops).

Using filter-flags with negating-flags, you can select exactly the
flagstates you want, both required and prohibited.

Then with negating-flags in modflags, you can set and clear every flag

  #> Q umfLT-Pmf  # select sites with u,m,f only. enable print, turn off m,f leave u

Its not an important feature, but it does fill out the logic.
and the patch is tiny, and feels more symmetrical.
---
 Documentation/admin-guide/dynamic-debug-howto.rst | 10 ++++++----
 lib/dynamic_debug.c                               |  6 ++++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 45d3adf889ba..10e514237e83 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -257,9 +257,11 @@ only callsites with ``u`` and ``f`` cleared.
 
 Flagsets cannot contain ``pP`` 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; '-pU' means disable
+printing, and mark that callsite with the user-flag to create a group,
+for optional further manipulation.  Generally, '+p' and '-p' is your
+main choice, and use of negating flags in modflags is rare.
 
 Notes::
 
@@ -269,7 +271,7 @@ For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only
 For display, the flags are preceded by ``=``
 (mnemonic: what the flags are currently equal to).
 
-Note the regexp ``^[-+=][flmptu_]+$`` matches a flags specification.
+Note the regexp ``/^[-+=][flmptu_]+$/i`` matches a flags specification.
 To clear all flags at once, use ``=_`` or ``-flmptu``.
 
 
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b02cde1cfc2f..d67fbbc5317f 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -486,15 +486,17 @@ 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;
 	}
 
-- 
2.26.2