[3/5] dyndbg: add DEFINE_DYNAMIC_DEBUG_CLASSBITS macro

Commit Message

Jim Cromie March 11, 2022, 4:47 a.m. UTC

DEFINE_DYNAMIC_DEBUG_CLASSBITS(fsname, var, bitmap_desc, classes..)
allows users to create a drm.debug style (bitmap) sysfs interface, to
control sets of pr_debug's according to their .class_id's

This wraps existing "class" keyword and behavior:

   bash-5.1# echo <<END  > /proc/dynamic_debug/control
   > module drm class 0 +p
   > module drm class 2 +p
   > END

With the macro used (in a client), this is basically equivalent:

   # but this also clears other flags, if theyre set
   echo 0x05 > /sys/module/drm/parameters/debug

To use:

DEFINE_DYNAMIC_DEBUG_CLASSBITS(debug, __drm_debug, "pmfl",
	"drm.debug - bits => categories:",
	/* vector of uint:4 symbols, ala enum drm_debug_category, 15 is EOL */
	DRM_UT_CORE,
	DRM_UT_DRIVER,
	DRM_UT_KMS ... );

The 3rd arg is a string with any of the dyndbg.flags [pmflt_]+
Full exposure of the flags here lets the module author:

- fully customize/take-over the decorations of enabled sites.
  generally leaving decorations to user is preferred.

- aim the debug-stream:
  now printk, later tracefs.
  using both together means more work (p or T, in practice)
  iface doesn't care about new flags added later

- declare 2 separate sysfs-knobs, one each for p, T, if desired.

- decorations are per callsite,
  shared across sysfs-knobs for any controlled classes

To support the macro, the patch adds:

 - int param_set_dyndbg_classbits()
 - int param_get_dyndbg_classbits()
 - struct kernel_param_ops param_ops_dyndbg_classbits

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_bitmap_param containing:

A- the vector of classes (drm.debug "categories") being controlled

This in-line vector of constants (uint [0-14]) specifies a sequence of
controlling bits (by position, starting at 0) with the values naming
the class_id's mapped to that bit.

A value of _DPRINTK_SITE_UNCLASSED terminates the vector processing by
param_set_dyndbg_classbits(), and is appended by the macro to insure a
defined termination after max 15 classes are applied.

Technically, the vector is a flex-array, but its size is practically
limited to max 15 in length (repeats are pointless).

B- a pointer to the user module's ulong holding the bits/state.

By accessing client's bit-state, we coordinate with existing code
that still uses drm_debug_enabled(), so they work unchanged.
The change to ulong allows use of BIT() etc.

NOTES:

_DPRINTK_SITE_UNCLASSED = 15, ie 2**CLS_BITS-1, deserves special
mention; it already marks all existing pr-debug callsites, only the
new drm.debug callsites are initialized to other (DRM_UT_*) values.

_DPRINTK_SITE_UNCLASSED is used in param_set_dyndbg_classbits() to
limit the range of bits that are processed to what fits in uint:4.
It also terminates the class-id list passed into the macro, so dont
use it halfway through your list of classes-to-control.

param_set_dyndbg_classbits() compares new vs old bits, and only
updates each class on changes.  This maximally preserves the
underlying state, which may have been customized at some point via
`echo $cmd >control`.  So if users really want to know that all
prdbgs are set precisely, they must pre-clear then set.

Identity mapping in (A) is encouraged.  Your vector should exclude 15,
if used, it terminates the list prematurely; any following bit
mappings will be ignored (it is the default/non category).

The whole (A) vector/list passed to the macro is:

- not strictly needed: 0-N bits are scanned, only N is needed in the
  macro interface to do this, not the whole list.

- 0-N list allows juggling the bit->class map
  Identity map is preferred.
  15 terminates list if used. (macro impl does this)

That said, (A) is self-documenting; the explicit list is greppable,
'DRM_UT_*' provides lots of clues.  Further, it could be upgraded,
something like:

  _pick_sym_(DRM_UT_CORE, "mumble something useful about CORE debug")

_pick_sym_(a,b) a		// gives us what we need here
_pick_help_(a,b) #a " : " b	// mod-info fodder

Signed-off-by: Jim Cromie <[e-mail]>
---
 include/linux/dynamic_debug.h | 50 +++++++++++++++++++++++
 lib/dynamic_debug.c           | 77 +++++++++++++++++++++++++++++++++++
 2 files changed, 127 insertions(+)

Patch

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index d4b48f3cc6e8..e83c4e36ad29 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -209,6 +209,10 @@  void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 				   KERN_DEBUG, prefix_str, prefix_type,	\
 				   rowsize, groupsize, buf, len, ascii)
 
+struct kernel_param;
+int param_set_dyndbg_classbits(const char *instr, const struct kernel_param *kp);
+int param_get_dyndbg_classbits(char *buffer, const struct kernel_param *kp);
+
 #else /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
 #include <linux/string.h>
@@ -255,6 +259,52 @@  static inline int dynamic_debug_exec_queries(const char *query, const char *modn
 	return 0;
 }
 
+struct kernel_param;
+static inline int param_set_dyndbg_classbits(const char *instr, const struct kernel_param *kp)
+{ return 0; }
+static inline int param_get_dyndbg_classbits(char *buffer, const struct kernel_param *kp)
+{ return 0; }
+
 #endif /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
+#define FLAGS_LEN 8
+struct dyndbg_classbits_param {
+	unsigned long *bits;		/* ref to shared state */
+	const char flags[FLAGS_LEN];	/* toggle these flags on bit-changes */
+	const int classes[];		/* indexed by bitpos */
+};
+
+#if defined(CONFIG_DYNAMIC_DEBUG) || defined(CONFIG_DYNAMIC_DEBUG_CORE)
+/**
+ * DEFINE_DYNAMIC_DEBUG_CLASSBITS() - bitmap control of classed pr_debugs
+ * @sysname: sysfs-node name
+ * @_var:    C-identifier holding bit-vector (Bits 0-14 are usable)
+ * @_flgs:   string with dyndbg flags: 'p' and/or 'T', and maybe "fmlt" also.
+ * @desc:    string summarizing the controls provided
+ * @classes: vector of callsite.class_id's (uint:4, 15 is reserved)
+ *
+ * This macro implements a DRM.debug API style bitmap, mapping bits
+ * 0-14 to classes of prdbg's, as initialized in their .class_id fields.
+ * @_flgs chooses the debug recipient; p - syslog, T - tracefs, and
+ * can include log decorations; m - module, f - function, l - line_num
+ */
+#define DEFINE_DYNAMIC_DEBUG_CLASSBITS(fsname, _var, _flgs, desc, ...)	\
+	MODULE_PARM_DESC(fsname, desc);					\
+	static struct dyndbg_classbits_param ddcats_##_var = {		\
+		.bits = &(_var),					\
+		.flags = _flgs,						\
+		.classes = { __VA_ARGS__, _DPRINTK_SITE_UNCLASSED }	\
+	};								\
+	module_param_cb(fsname, &param_ops_dyndbg_classbits,		\
+			&ddcats_##_var, 0644)
+
+extern const struct kernel_param_ops param_ops_dyndbg_classbits;
+
+#else /* no dyndbg configured, throw error on macro use */
+
+#define DEFINE_DYNAMIC_DEBUG_CLASSBITS(fsname, var, bitmap_desc, ...)	\
+	BUILD_BUG_ON_MSG(1, "CONFIG_DYNAMIC_DEBUG* needed to use this macro: " #fsname)
+
+#endif
+
 #endif
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index ee2129becacc..704361af5b23 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -611,6 +611,83 @@  int dynamic_debug_exec_queries(const char *query, const char *modname)
 }
 EXPORT_SYMBOL_GPL(dynamic_debug_exec_queries);
 
+#ifdef CONFIG_MODULES
+#define KP_MOD_NAME kp->mod->name
+#else
+#define KP_MOD_NAME NULL /* wildcard */
+#endif
+#define FMT_QUERY_SIZE 128 /* typically need <40 */
+/**
+ * param_set_dyndbg_classbits - 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
+ * DEFINE_DYNAMIC_DEBUG_BITGRPS.classbits argument.
+ *
+ * Returns: 0 or <0 if error.
+ */
+int param_set_dyndbg_classbits(const char *instr, const struct kernel_param *kp)
+{
+	unsigned long inbits;
+	int rc, i, matches = 0, totct = 0;
+	char query[FMT_QUERY_SIZE];
+	const struct dyndbg_classbits_param *dcp = kp->arg;
+
+	if (!dcp) {
+		pr_err("set_dyndbg_classbits: no bits=>queries map\n");
+		return -EINVAL;
+	}
+	rc = kstrtoul(instr, 0, &inbits);
+	if (rc) {
+		pr_err("set_dyndbg_classbits: expecting unsigned int\n");
+		return rc;
+	}
+	vpr_info("set_dyndbg_classbits: new 0x%lx old 0x%lx\n", inbits, *dcp->bits);
+
+	for (i = 0; (i < _DPRINTK_SITE_UNCLASSED &&
+		     dcp->classes[i] < _DPRINTK_SITE_UNCLASSED); i++) {
+
+		if (test_bit(i, &inbits) == test_bit(i, dcp->bits))
+			continue;
+		snprintf(query, FMT_QUERY_SIZE, "class %d %cT",
+			 dcp->classes[i], test_bit(i, &inbits) ? '+' : '-');
+
+		matches = ddebug_exec_queries(query, KP_MOD_NAME);
+
+		v2pr_info("bit-%d: %d matches on class:%u\n", i,
+			  matches, dcp->classes[i]);
+		totct += matches;
+	}
+	*dcp->bits = inbits;
+	vpr_info("total matches: %d\n", totct);
+	return 0;
+}
+EXPORT_SYMBOL(param_set_dyndbg_classbits);
+
+/**
+ * param_get_dyndbg_classbits - classbits 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_classbits(char *buffer, const struct kernel_param *kp)
+{
+	const struct dyndbg_classbits_param *p = kp->arg;
+	unsigned long val = *p->bits;
+
+	return scnprintf(buffer, PAGE_SIZE, "0x%lx\n", val);
+}
+EXPORT_SYMBOL(param_get_dyndbg_classbits);
+
+const struct kernel_param_ops param_ops_dyndbg_classbits = {
+	.set = param_set_dyndbg_classbits,
+	.get = param_get_dyndbg_classbits,
+};
+EXPORT_SYMBOL(param_ops_dyndbg_classbits);
+
 #define PREFIX_SIZE 64
 
 static int remaining(int wrote)