dynamic_debug: describe_flags with '=[pmflt_]*'

Change describe_flags() to emit '=[pmflt_]+' for current callsite
flags, or just '=_' when they're disabled.  Having '=' in output
allows a more selective grep expression; in contrast '-' may appear
in filenames, line-ranges, and format-strings.  '=' also has better
mnemonics, saying; "the current setting is equal to <flags>".

This allows grep "=_" <dbgfs>/dynamic_debug/control to see disabled
callsites while avoiding the many occurrences of " = " seen in format
strings.

Enlarge flagsbufs to handle additional flag char, and alter
ddebug_parse_flags() to allow flags=0, so that user can turn off all
debug flags via:

  ~# echo =_ > <dbgfs>/dynamic_debug/control
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/dynamic_debug.h

@@ -21,7 +21,8 @@ struct _ddebug {
  	 * The bits here are changed dynamically when the user
 	 * writes commands to <debugfs>/dynamic_debug/control
 	 */
-#define _DPRINTK_FLAGS_PRINT   (1<<0)  /* printk() a message using the format */
+#define _DPRINTK_FLAGS_NONE	0
+#define _DPRINTK_FLAGS_PRINT	(1<<0) /* printk() a message using the format */
 #define _DPRINTK_FLAGS_INCL_MODNAME	(1<<1)
 #define _DPRINTK_FLAGS_INCL_FUNCNAME	(1<<2)
 #define _DPRINTK_FLAGS_INCL_LINENO	(1<<3)

lib/dynamic_debug.c

@@ -75,6 +75,7 @@ static struct { unsigned flag:8; char opt_char; } opt_array[] = {
 	{ _DPRINTK_FLAGS_INCL_FUNCNAME, 'f' },
 	{ _DPRINTK_FLAGS_INCL_LINENO, 'l' },
 	{ _DPRINTK_FLAGS_INCL_TID, 't' },
+	{ _DPRINTK_FLAGS_NONE, '_' },
 };
 
 /* format a string into buf[] which describes the _ddebug's flags */
@@ -84,12 +85,12 @@ static char *ddebug_describe_flags(struct _ddebug *dp, char *buf,
 	char *p = buf;
 	int i;
 
-	BUG_ON(maxlen < 4);
+	BUG_ON(maxlen < 6);
 	for (i = 0; i < ARRAY_SIZE(opt_array); ++i)
 		if (dp->flags & opt_array[i].flag)
 			*p++ = opt_array[i].opt_char;
 	if (p == buf)
-		*p++ = '-';
+		*p++ = '_';
 	*p = '\0';
 
 	return buf;
@@ -108,7 +109,7 @@ static void ddebug_change(const struct ddebug_query *query,
 	struct ddebug_table *dt;
 	unsigned int newflags;
 	unsigned int nfound = 0;
-	char flagbuf[8];
+	char flagbuf[10];
 
 	/* search for matching ddebugs */
 	mutex_lock(&ddebug_lock);
@@ -152,7 +153,7 @@ static void ddebug_change(const struct ddebug_query *query,
 				continue;
 			dp->flags = newflags;
 			if (verbose)
-				pr_info("changed %s:%d [%s]%s %s\n",
+				pr_info("changed %s:%d [%s]%s =%s\n",
 					dp->filename, dp->lineno,
 					dt->mod_name, dp->function,
 					ddebug_describe_flags(dp, flagbuf,
@@ -370,8 +371,6 @@ static int ddebug_parse_flags(const char *str, unsigned int *flagsp,
 		if (i < 0)
 			return -EINVAL;
 	}
-	if (flags == 0)
-		return -EINVAL;
 	if (verbose)
 		pr_info("flags=0x%x\n", flags);
 
@@ -666,7 +665,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
 {
 	struct ddebug_iter *iter = m->private;
 	struct _ddebug *dp = p;
-	char flagsbuf[8];
+	char flagsbuf[10];
 
 	if (verbose)
 		pr_info("called m=%p p=%p\n", m, p);
@@ -677,10 +676,10 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
 		return 0;
 	}
 
-	seq_printf(m, "%s:%u [%s]%s %s \"",
-		   dp->filename, dp->lineno,
-		   iter->table->mod_name, dp->function,
-		   ddebug_describe_flags(dp, flagsbuf, sizeof(flagsbuf)));
+	seq_printf(m, "%s:%u [%s]%s =%s \"",
+		dp->filename, dp->lineno,
+		iter->table->mod_name, dp->function,
+		ddebug_describe_flags(dp, flagsbuf, sizeof(flagsbuf)));
 	seq_escape(m, dp->format, "\t\r\n\"");
 	seq_puts(m, "\"\n");