[PATCH v2 08/27] dyndbg: add drm.debug style bitmap support

[Jim Cromie]

Add kernel_param_ops and callbacks to implement a bitmap in a
sysfs-node.  IE, add these:

 - int param_set_dyndbg_classes()
 - int param_get_dyndbg_classes()
 - struct kernel_param_ops param_ops_dyndbg_classes

Following the model of kernel/params.c STANDARD_PARAM_DEFS, these are
non-static and exported.

get/set use an augmented kernel_param; the arg refs a new struct
dyndbg_classes_param, initialized by the macro, containing:

BITS: a pointer to the user module's ulong holding the bits/state.
By ref'g the client's bit-state, we coordinate with existing code that
uses it, so it works unchanged; for example drm_debug_enabled().  The
change to ulong allows use of BIT() etc.

FLAGS: dyndbg.flags toggled by bit-changes. Usually just "p".

MAP: a pointer to struct ddebug_known_classes, which maps those
class-names to pr_debug.class_ids 0..N.

Using the sys-node, with dynamic_debug.verbose=1:

bash-5.1# echo 1 > /sys/module/drm/parameters/debug
[   29.821298] dyndbg: set_dyndbg_classes: new 0x1 current 0x0
[   29.822841] dyndbg: query 0: "class DRM_UT_CORE +p" mod:*
[   29.824348] dyndbg: no matches for query
[   29.825428] dyndbg: total matches: 0

Signed-off-by: Jim Cromie <jim.cromie at gmail.com>
---
 include/linux/dynamic_debug.h | 17 ++++++++
 lib/dynamic_debug.c           | 81 +++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 328722ba2d8e..e9e6d0f503f3 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -85,6 +85,11 @@ struct ddebug_known_classes_map {
 		.classes = { __VA_ARGS__ }				\
 	}
 
+struct ddebug_classes_bitmap_param {
+	unsigned long *bits;
+	char flags[8];
+	const struct ddebug_known_classes_map *map;
+};
 
 #if defined(CONFIG_DYNAMIC_DEBUG_CORE)
 
@@ -237,6 +242,10 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 int  dynamic_debug_register_classes(struct ddebug_known_classes_map *map);
 void dynamic_debug_unregister_classes(struct ddebug_known_classes_map *map);
 
+struct kernel_param;
+int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp);
+int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp);
+
 #else /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
 #include <linux/string.h>
@@ -283,6 +292,14 @@ static inline int dynamic_debug_register_classes(const struct ddebug_known_class
 static inline void dynamic_debug_unregister_classes(struct ddebug_known_classes_map *map)
 {}
 
+struct kernel_param;
+static inline int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp)
+{ return 0; }
+static inline int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
+{ return 0; }
+
 #endif /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
+extern const struct kernel_param_ops param_ops_dyndbg_classes;
+
 #endif
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b1aaf8893cdf..b67bf9efec07 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -597,6 +597,87 @@ static int ddebug_exec_queries(char *query, const char *modname)
 	return nfound;
 }
 
+static int do_callback_changes(const struct ddebug_classes_bitmap_param *dcp,
+			       int bitpos, unsigned long *inbits)
+{
+#define QUERY_SIZE 128
+	char query[QUERY_SIZE];
+	int matches;
+
+	snprintf(query, QUERY_SIZE, "class %s %c%s", dcp->map->classes[bitpos],
+		 test_bit(bitpos, inbits) ? '+' : '-', dcp->flags);
+
+	matches = ddebug_exec_queries(query, NULL);
+
+	v2pr_info("bit-%d: %d matches on class:%s\n", bitpos,
+		  matches, dcp->map->classes[bitpos]);
+
+	return matches;
+}
+
+/**
+ * param_set_dyndbg_classes - bits => categories >control setter
+ * @instr: string echo>d to sysfs
+ * @kp:    kp->arg has state: bits, map
+ *
+ * Enable/disable prdbgs by their "category", as specified in the
+ * arguments to DEFINE_DYNAMIC_DEBUG_CLASSES.
+ *
+ * Returns: 0 or <0 if error.
+ */
+int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp)
+{
+	const struct ddebug_classes_bitmap_param *dcp = kp->arg;
+	unsigned long inbits;
+	int rc, i, totct = 0;
+
+	if (!dcp || !dcp->map) {
+		pr_err("set_dyndbg_classes: no bits=>queries map\n");
+		return -EINVAL;
+	}
+	rc = kstrtoul(instr, 0, &inbits);
+	if (rc) {
+		pr_err("set_dyndbg_classes: expecting bits/integer\n");
+		return -EINVAL;
+	}
+	vpr_info("set_dyndbg_classes: new 0x%lx current 0x%lx\n", inbits, *dcp->bits);
+
+	for (i = 0; i < dcp->map->length; i++) {
+
+		if (test_bit(i, &inbits) == test_bit(i, dcp->bits))
+			continue;
+
+		totct += do_callback_changes(dcp, i, &inbits);
+	}
+	*dcp->bits = inbits;
+	vpr_info("total matches: %d\n", totct);
+	return 0;
+}
+EXPORT_SYMBOL(param_set_dyndbg_classes);
+
+/**
+ * param_get_dyndbg_classes - classes reader
+ * @buffer: string description of controlled bits -> classes
+ * @kp:     kp->arg has state: bits, map
+ *
+ * Reads last written bits, underlying prdbg state may have changed since.
+ * Returns: #chars written or <0 on error
+ */
+int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
+{
+	const struct ddebug_classes_bitmap_param *p = kp->arg;
+	unsigned long val = *p->bits;
+
+	return scnprintf(buffer, PAGE_SIZE, "0x%lx\n", val);
+}
+EXPORT_SYMBOL(param_get_dyndbg_classes);
+
+const struct kernel_param_ops param_ops_dyndbg_classes = {
+	.set = param_set_dyndbg_classes,
+	.get = param_get_dyndbg_classes,
+};
+EXPORT_SYMBOL(param_ops_dyndbg_classes);
+
 #define PREFIX_SIZE 64
 
 static int remaining(int wrote)
-- 
2.35.3