dyndbg: refine export, rename to dynamic_debug_exec_queries()

commit 4c0d77828d4f ("dyndbg: export ddebug_exec_queries") had a few
problems:
 - broken non DYNAMIC_DEBUG_CORE configs, sparse warning
 - the exported function modifies query string, breaks on RO strings.
 - func name follows internal convention, shouldn't be exposed as is.

1st is fixed in header with ifdefd function prototype or stub defn.
Also remove an obsolete HAVE-symbol ifdef-comment, and add others.

Fix others by wrapping existing internal function with a new one,
named in accordance with module-prefix naming convention, before
export hits v5.9.0.  In new function, copy query string to a local
buffer, so users can pass hard-coded/RO queries, and internal function
can be used unchanged.

Fixes: 4c0d77828d4f ("dyndbg: export ddebug_exec_queries")
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200831182210.850852-3-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 41 insertions, 6 deletions

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index aa9ff9e1c0b3..8aa0c7c2608c 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -49,6 +49,10 @@ struct _ddebug {
 
 
 #if defined(CONFIG_DYNAMIC_DEBUG_CORE)
+
+/* exported for module authors to exercise >control */
+int dynamic_debug_exec_queries(const char *query, const char *modname);
+
 int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 				const char *modname);
 extern int ddebug_remove_module(const char *mod_name);
@@ -105,7 +109,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 	static_branch_unlikely(&descriptor.key.dd_key_false)
 #endif
 
-#else /* !HAVE_JUMP_LABEL */
+#else /* !CONFIG_JUMP_LABEL */
 
 #define _DPRINTK_KEY_INIT
 
@@ -117,7 +121,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 	unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
 #endif
 
-#endif
+#endif /* CONFIG_JUMP_LABEL */
 
 #define __dynamic_func_call(id, fmt, func, ...) do {	\
 	DEFINE_DYNAMIC_DEBUG_METADATA(id, fmt);		\
@@ -172,10 +176,11 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 				   KERN_DEBUG, prefix_str, prefix_type,	\
 				   rowsize, groupsize, buf, len, ascii)
 
-#else
+#else /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
 #include <linux/string.h>
 #include <linux/errno.h>
+#include <linux/printk.h>
 
 static inline int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 				    const char *modname)
@@ -210,6 +215,13 @@ static inline int ddebug_dyndbg_module_param_cb(char *param, char *val,
 		print_hex_dump(KERN_DEBUG, prefix_str, prefix_type,	\
 				rowsize, groupsize, buf, len, ascii);	\
 	} while (0)
-#endif
+
+static inline int dynamic_debug_exec_queries(const char *query, const char *modname)
+{
+	pr_warn("kernel not built with CONFIG_DYNAMIC_DEBUG_CORE\n");
+	return 0;
+}
+
+#endif /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
 #endif
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 01b7d0210412..08e4b057514c 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -525,7 +525,7 @@ static int ddebug_exec_query(char *query_string, const char *modname)
    last error or number of matching callsites.  Module name is either
    in param (for boot arg) or perhaps in query string.
 */
-int ddebug_exec_queries(char *query, const char *modname)
+static int ddebug_exec_queries(char *query, const char *modname)
 {
 	char *split;
 	int i, errs = 0, exitcode = 0, rc, nfound = 0;
@@ -557,7 +557,30 @@ int ddebug_exec_queries(char *query, const char *modname)
 		return exitcode;
 	return nfound;
 }
-EXPORT_SYMBOL_GPL(ddebug_exec_queries);
+
+/**
+ * dynamic_debug_exec_queries - select and change dynamic-debug prints
+ * @query: query-string described in admin-guide/dynamic-debug-howto
+ * @modname: string containing module name, usually &module.mod_name
+ *
+ * This uses the >/proc/dynamic_debug/control reader, allowing module
+ * authors to modify their dynamic-debug callsites. The modname is
+ * canonically struct module.mod_name, but can also be null or a
+ * module-wildcard, for example: "drm*".
+ */
+int dynamic_debug_exec_queries(const char *query, const char *modname)
+{
+	int rc;
+	char *qry = kstrndup(query, PAGE_SIZE, GFP_KERNEL);
+
+	if (!query)
+		return -ENOMEM;
+
+	rc = ddebug_exec_queries(qry, modname);
+	kfree(qry);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dynamic_debug_exec_queries);
 
 #define PREFIX_SIZE 64