[PATCH 01/16] dyndbg-docs: eschew file /full/path query in docs

[PATCH 01/16] dyndbg-docs: eschew file /full/path query in docs

[Jim Cromie]

Regarding:
commit 2b6783191da7 ("dynamic_debug: add trim_prefix() to provide source-root relative paths")
commit a73619a845d5 ("kbuild: use -fmacro-prefix-map to make __FILE__ a relative path")

2nd commit broke dynamic-debug's "file $fullpath" query form, but
nobody noticed because 1st commit had trimmed prefixes from
control-file output, so the click-copy-pasting of fullpaths into new
queries had ceased; that query form became unused.

Removing the function is cleanest, but it could be useful in
old-compiler corner cases, where __FILE__ still has /full/path,
and it safely does nothing otherwize.

So instead, quietly deprecate "file /full/path" query form, by
removing all /full/paths examples in the docs.  I skipped adding a
back-compat note.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 .../admin-guide/dynamic-debug-howto.rst       | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 0dc2eb8e44e5..2854d418b31b 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -65,10 +65,10 @@ statements via::
 
   nullarbor:~ # cat <debugfs>/dynamic_debug/control
   # filename:lineno [module]function flags format
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline       : %d\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth         : %d\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests     : %d\012"
+  net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
+  net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline       : %d\012"
+  net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth         : %d\012"
+  net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests     : %d\012"
   ...
 
 
@@ -88,7 +88,7 @@ the debug statement callsites with any non-default flags::
 
   nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
   # filename:lineno [module]function flags format
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
+  net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
 
 Command Language Reference
 ==========================
@@ -161,13 +161,12 @@ func
 	func svc_tcp_accept
 
 file
-    The given string is compared against either the full pathname, the
-    src-root relative pathname, or the basename of the source file of
-    each callsite.  Examples::
+    The given string is compared against either the src-root relative
+    pathname, or the basename of the source file of each callsite.
+    Examples::
 
 	file svcsock.c
-	file kernel/freezer.c
-	file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
+	file kernel/freezer.c	# ie column 1 of control file
 
 module
     The given string is compared against the module name
-- 
2.26.2

[PATCH 09/16] dyndbg: accept 'file foo.c:func1' and 'file foo.c:10-100'

[Jim Cromie]

Accept these additional query forms:

   echo "file $filestr +_" > control

       path/to/file.c:100	# as from control, column 1
       path/to/file.c:1-100	# or any legal line-range
       path/to/file.c:func_A	# as from an editor/browser
       path/to/file.c:drm_\*	# wildcards still work
       path/to/file.c:*_foo	# lead wildcard too

1st 2 examples are treated as line-ranges, 3,4 are treated as func's

Doc these changes, and sprinkle in a few extra wild-card examples and
trailing # explanation texts.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 .../admin-guide/dynamic-debug-howto.rst       |  5 +++++
 lib/dynamic_debug.c                           | 20 ++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 2854d418b31b..880d33d1782f 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -159,6 +159,7 @@ func
     of each callsite.  Example::
 
 	func svc_tcp_accept
+	func *recv*		# in rfcomm, bluetooth, ping, tcp
 
 file
     The given string is compared against either the src-root relative
@@ -167,6 +168,9 @@ file
 
 	file svcsock.c
 	file kernel/freezer.c	# ie column 1 of control file
+	file drivers/usb/*	# all callsites under it
+	file inode.c:start_*	# parse :tail as a func (above)
+	file inode.c:1-100	# parse :tail as a line-range (above)
 
 module
     The given string is compared against the module name
@@ -176,6 +180,7 @@ module
 
 	module sunrpc
 	module nfsd
+	module drm*	# both drm, drm_kms_helper
 
 format
     The given string is searched for in the dynamic debug format
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index d43bc3547d3a..8f250c67acbe 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -321,6 +321,8 @@ static int parse_linerange(struct ddebug_query *query, const char *first)
 	} else {
 		query->last_lineno = query->first_lineno;
 	}
+	vpr_info("parsed line %d-%d\n", query->first_lineno,
+		 query->last_lineno);
 	return 0;
 }
 
@@ -357,6 +359,7 @@ static int ddebug_parse_query(char *words[], int nwords,
 {
 	unsigned int i;
 	int rc = 0;
+	char *fline;
 
 	/* check we have an even number of words */
 	if (nwords % 2 != 0) {
@@ -373,7 +376,22 @@ static int ddebug_parse_query(char *words[], int nwords,
 		if (!strcmp(words[i], "func")) {
 			rc = check_set(&query->function, words[i+1], "func");
 		} else if (!strcmp(words[i], "file")) {
-			rc = check_set(&query->filename, words[i+1], "file");
+			if (check_set(&query->filename, words[i+1], "file"))
+				return -EINVAL;
+
+			/* tail :$info is function or line-range */
+			fline = strchr(query->filename, ':');
+			if (!fline)
+				break;
+			*fline++ = '\0';
+			if (isalpha(*fline) || *fline == '*' || *fline == '?') {
+				/* take as function name */
+				if (check_set(&query->function, fline, "func"))
+					return -EINVAL;
+			} else
+				if (parse_linerange(query, fline))
+					return -EINVAL;
+
 		} else if (!strcmp(words[i], "module")) {
 			rc = check_set(&query->module, words[i+1], "module");
 		} else if (!strcmp(words[i], "format")) {
-- 
2.26.2

Re: [PATCH 09/16] dyndbg: accept 'file foo.c:func1' and 'file foo.c:10-100'

[Jason Baron]

On 6/5/20 12:26 PM, Jim Cromie wrote:
> Accept these additional query forms:
> 
>    echo "file $filestr +_" > control
> 
>        path/to/file.c:100	# as from control, column 1
>        path/to/file.c:1-100	# or any legal line-range
>        path/to/file.c:func_A	# as from an editor/browser
>        path/to/file.c:drm_\*	# wildcards still work
>        path/to/file.c:*_foo	# lead wildcard too
> 
> 1st 2 examples are treated as line-ranges, 3,4 are treated as func's
> 
> Doc these changes, and sprinkle in a few extra wild-card examples and
> trailing # explanation texts.
> 
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> ---
>  .../admin-guide/dynamic-debug-howto.rst       |  5 +++++
>  lib/dynamic_debug.c                           | 20 ++++++++++++++++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
> index 2854d418b31b..880d33d1782f 100644
> --- a/Documentation/admin-guide/dynamic-debug-howto.rst
> +++ b/Documentation/admin-guide/dynamic-debug-howto.rst
> @@ -159,6 +159,7 @@ func
>      of each callsite.  Example::
>  
>  	func svc_tcp_accept
> +	func *recv*		# in rfcomm, bluetooth, ping, tcp
>  
>  file
>      The given string is compared against either the src-root relative
> @@ -167,6 +168,9 @@ file
>  
>  	file svcsock.c
>  	file kernel/freezer.c	# ie column 1 of control file
> +	file drivers/usb/*	# all callsites under it
> +	file inode.c:start_*	# parse :tail as a func (above)
> +	file inode.c:1-100	# parse :tail as a line-range (above)
>  
>  module
>      The given string is compared against the module name
> @@ -176,6 +180,7 @@ module
>  
>  	module sunrpc
>  	module nfsd
> +	module drm*	# both drm, drm_kms_helper
>  
>  format
>      The given string is searched for in the dynamic debug format
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index d43bc3547d3a..8f250c67acbe 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -321,6 +321,8 @@ static int parse_linerange(struct ddebug_query *query, const char *first)
>  	} else {
>  		query->last_lineno = query->first_lineno;
>  	}
> +	vpr_info("parsed line %d-%d\n", query->first_lineno,
> +		 query->last_lineno);
>  	return 0;
>  }
>  
> @@ -357,6 +359,7 @@ static int ddebug_parse_query(char *words[], int nwords,
>  {
>  	unsigned int i;
>  	int rc = 0;
> +	char *fline;
>  
>  	/* check we have an even number of words */
>  	if (nwords % 2 != 0) {
> @@ -373,7 +376,22 @@ static int ddebug_parse_query(char *words[], int nwords,
>  		if (!strcmp(words[i], "func")) {
>  			rc = check_set(&query->function, words[i+1], "func");
>  		} else if (!strcmp(words[i], "file")) {
> -			rc = check_set(&query->filename, words[i+1], "file");
> +			if (check_set(&query->filename, words[i+1], "file"))
> +				return -EINVAL;
> +
> +			/* tail :$info is function or line-range */
> +			fline = strchr(query->filename, ':');
> +			if (!fline)
> +				break;
> +			*fline++ = '\0';
> +			if (isalpha(*fline) || *fline == '*' || *fline == '?') {
> +				/* take as function name */
> +				if (check_set(&query->function, fline, "func"))
> +					return -EINVAL;
> +			} else
> +				if (parse_linerange(query, fline))
> +					return -EINVAL;
> +

coding style here is to use braces for both branches.



>  		} else if (!strcmp(words[i], "module")) {
>  			rc = check_set(&query->module, words[i+1], "module");
>  		} else if (!strcmp(words[i], "format")) {
> 

[PATCH 13/16] dyndbg: extend ddebug_parse_flags to accept optional leading filter-flags

[Jim Cromie]

change ddebug_parse_flags to accept optional filterflags before OP.
this now sets the parameter added in ~1

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 .../admin-guide/dynamic-debug-howto.rst       | 18 +++++++----
 lib/dynamic_debug.c                           | 30 ++++++++++---------
 2 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 880d33d1782f..250ab30e2080 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -212,13 +212,19 @@ line
 	line -1605          // the 1605 lines from line 1 to line 1605
 	line 1600-          // all lines from line 1600 to the end of the file
 
-The flags specification comprises a change operation followed
-by one or more flag characters.  The change operation is one
-of the characters::
+Flags Specification::
 
-  -    remove the given flags
-  +    add the given flags
-  =    set the flags to the given flags
+  flagspec	::= filterflags? OP modflags
+  filterflags	::= flagset
+  modflags	::= flagset
+  flagset	::= ([pfmltu_] | [PFMLTU_])+	# also cant have pP etc
+  OP		::= [-+=]
+
+OP: modify callsites per following flagset::
+
+  -    remove the following flags
+  +    add the following flags
+  =    set the flags to the following flags
 
 The flags are::
 
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 32eb7d9545c7..90061833ef3f 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -440,34 +440,36 @@ static int ddebug_read_flags(const char *str, struct flagsettings *f)
 }
 
 /*
- * Parse `str' as a flags specification, format [-+=][p]+.
- * Sets up *maskp and *flagsp to be used when changing the
- * flags fields of matched _ddebug's.  Returns 0 on success
- * or <0 on error.
+ * Parse `str' as a flags-spec, ie: [pfmlt_]*[-+=][pfmlt_]+
+ * Fills flagsettings provided.  Returns 0 on success or <0 on error.
  */
-
 static int ddebug_parse_flags(const char *str,
 			      struct flagsettings *mods,
 			      struct flagsettings *filter)
 {
 	int op;
+	char *opp = strpbrk(str, "-+=");
 
-	switch (*str) {
-	case '+':
-	case '-':
-	case '=':
-		op = *str++;
-		break;
-	default:
-		pr_err("bad flag-op %c, at start of %s\n", *str, str);
+	if (!opp) {
+		pr_err("no OP given in %s\n", str);
 		return -EINVAL;
 	}
+	op = *opp;
 	vpr_info("op='%c'\n", op);
 
+	if (opp != str) {
+		/* filterflags precedes OP, grab it */
+		*opp++ = '\0';
+		if (ddebug_read_flags(str, filter))
+			return -EINVAL;
+		str = opp;
+	} else
+		str++;
+
 	if (ddebug_read_flags(str, mods))
 		return -EINVAL;
 
-	/* calculate final flags, mask based upon op */
+	/* calculate final mods: flags, mask based upon op */
 	switch (op) {
 	case '=':
 		mods->mask = 0;
-- 
2.26.2

[PATCH 15/16] dyndbg: add user-flag, negating-flags, and filtering on flags

[Jim Cromie]

1. Add a user-flag [u] which works like the [pfmlt] flags, but has no
effect on callsite behavior; it allows incremental marking of
arbitrary sets of callsites.

2. Add [PFMLTU] flags, which negate their counterparts; P===!p etc.
And in ddebug_read_flags():
   current code does:	[pfmltu_] -> flags
   copy it to:		[PFMLTU_] -> mask

also disallow both of a pair: ie no 'pP', no true & false.

3. Add filtering ops into ddebug_change(), right after all the
callsite-property selections are complete.  These filter on the
callsite's current flagstate before applying modflags.

Why ?

The new user flag facilitates batching of changes.  By marking
individual callsites with 'u', a user can compose an arbitrary set of
changes, then activate them together by filtering on 'u':

  #> echo 'file foo.c +u; file bar.c +u' > control
  #> echo 'u+p' > control

The user flag isn't strictly needed, but with it you can avoid using
[fmlt] flags for marking, which would alter logging when enabled.

The negating flags allow filtering on either 0/1 for each flag.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 .../admin-guide/dynamic-debug-howto.rst       | 31 ++++++++++++++++---
 include/linux/dynamic_debug.h                 |  1 +
 lib/dynamic_debug.c                           | 31 ++++++++++++++-----
 3 files changed, 51 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 250ab30e2080..26a19f511afa 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -233,16 +233,39 @@ The flags are::
   l    Include line number in the printed message
   m    Include module name in the printed message
   t    Include thread ID in messages not generated from interrupt context
+  u    user flag, to mark callsites into a group
   _    No flags are set. (Or'd with others on input)
 
-For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag
-have meaning, other flags ignored.
+Additionally, the flag-chars ``[pflmtu]`` have negating flag-chars
+``[PFMLTU]``, which invert the meanings above.  Their use follows.
+
+Using Filters::
+
+Filter-flags specify an optional additional selector on pr_debug
+callsites; with them you can compose an arbitrary set of callsites, by
+iteratively marking them with ``+u``, then enabling them all with
+``u+p``.  You can also use ``fmlt`` flags for this, unless the format
+changes are inconvenient.
+
+Filters can also contain the negating flags, like ``UF``, which select
+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.
+
+Notes::
+
+For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only
+``p`` flag has meaning, other flags are ignored.
 
 For display, the flags are preceded by ``=``
 (mnemonic: what the flags are currently equal to).
 
-Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
-To clear all flags at once, use ``=_`` or ``-flmpt``.
+Note the regexp ``^[-+=][flmptu_]+$`` matches a flags specification.
+To clear all flags at once, use ``=_`` or ``-flmptu``.
 
 
 Debug messages during Boot Process
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 802480ea8708..a5d76f8f6b40 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -32,6 +32,7 @@ struct _ddebug {
 #define _DPRINTK_FLAGS_INCL_FUNCNAME	(1<<2)
 #define _DPRINTK_FLAGS_INCL_LINENO	(1<<3)
 #define _DPRINTK_FLAGS_INCL_TID		(1<<4)
+#define _DPRINTK_FLAGS_USR		(1<<5)
 #if defined DEBUG
 #define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
 #else
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index f0c0c31e91ea..ee92e93cf23d 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -83,13 +83,14 @@ static inline const char *trim_prefix(const char *path)
 	return path + skip;
 }
 
-static struct { unsigned flag:8; char opt_char; } opt_array[] = {
-	{ _DPRINTK_FLAGS_PRINT, 'p' },
-	{ _DPRINTK_FLAGS_INCL_MODNAME, 'm' },
-	{ _DPRINTK_FLAGS_INCL_FUNCNAME, 'f' },
-	{ _DPRINTK_FLAGS_INCL_LINENO, 'l' },
-	{ _DPRINTK_FLAGS_INCL_TID, 't' },
-	{ _DPRINTK_FLAGS_NONE, '_' },
+static struct { unsigned flag:8; char opt_char, not_char; } opt_array[] = {
+	{ _DPRINTK_FLAGS_PRINT,		'p', 'P' },
+	{ _DPRINTK_FLAGS_INCL_MODNAME,	'm', 'M' },
+	{ _DPRINTK_FLAGS_INCL_FUNCNAME,	'f', 'F' },
+	{ _DPRINTK_FLAGS_INCL_LINENO,	'l', 'L' },
+	{ _DPRINTK_FLAGS_INCL_TID,	't', 'T' },
+	{ _DPRINTK_FLAGS_NONE,		'_', '_' },
+	{ _DPRINTK_FLAGS_USR,		'u', 'U' },
 };
 
 struct flagsbuf { char buf[ARRAY_SIZE(opt_array)+1]; };
@@ -194,6 +195,13 @@ static int ddebug_change(const struct ddebug_query *query,
 			    dp->lineno > query->last_lineno)
 				continue;
 
+			/* filter for required flags */
+			if ((dp->flags & filter->flags) != filter->flags)
+				continue;
+			/* filter on prohibited bits */
+			if ((~dp->flags & filter->mask) != filter->mask)
+				continue;
+
 			nfound++;
 
 			newflags = (dp->flags & mods->mask) | mods->flags;
@@ -427,10 +435,17 @@ static int ddebug_read_flags(const char *str, struct flagsettings *f)
 			if (*str == opt_array[i].opt_char) {
 				f->flags |= opt_array[i].flag;
 				break;
+			} else if (*str == opt_array[i].not_char) {
+				f->mask |= opt_array[i].flag;
+				break;
 			}
 		}
 		if (i < 0) {
-			pr_err("unknown flag '%c' in \"%s\"\n", *str, str);
+			pr_err("unknown flag '%c'", *str);
+			return -EINVAL;
+		}
+		if (f->flags & f->mask) {
+			pr_err("flag '%c' conflicts with previous\n", *str);
 			return -EINVAL;
 		}
 	}
-- 
2.26.2

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

[Jim Cromie]

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).
Generally, you chose -p or +p 1st, then set or clear flags
accordingly.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 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 26a19f511afa..45470c9f0dad 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -252,9 +252,11 @@ 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::
 
@@ -264,7 +266,7 @@ 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 ee92e93cf23d..63ae6f77a0e4 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -485,15 +485,17 @@ 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