Index: sys/geom/geom.h
===================================================================
--- sys/geom/geom.h
+++ sys/geom/geom.h
@@ -346,6 +346,7 @@
 int g_write_data(struct g_consumer *cp, off_t offset, void *ptr, off_t length);
 int g_delete_data(struct g_consumer *cp, off_t offset, off_t length);
 void g_print_bio(struct bio *bp);
+void g_format_bio(struct sbuf *, struct bio *bp);
 int g_use_g_read_data(void *, off_t, void **, int);
 int g_use_g_write_data(void *, off_t, void *, int);
 
Index: sys/geom/geom_int.h
===================================================================
--- sys/geom/geom_int.h
+++ sys/geom/geom_int.h
@@ -37,9 +37,22 @@
  * $FreeBSD$
  */
 
+#pragma once
+
 LIST_HEAD(class_list_head, g_class);
 TAILQ_HEAD(g_tailq_head, g_geom);
 
+#define _GEOM_DEBUG(gcls, ctrlvar, loglvl, biop, formatstr, ...) do {	\
+	const int __control = (ctrlvar);				\
+	const int __level = (loglvl);					\
+									\
+	if (__control < __level)					\
+		break;							\
+									\
+	g_dbg_printf((gcls), (__control > 0) ? __level : -1, (biop),	\
+	    ": " formatstr, ## __VA_ARGS__);				\
+} while (0)
+
 extern int g_collectstats;
 #define G_STATS_PROVIDERS	1	/* Collect I/O stats for providers */
 #define G_STATS_CONSUMERS	2	/* Collect I/O stats for consumers */
@@ -60,7 +73,7 @@
 void g_confxml(void *, int flag);
 void g_conf_specific(struct sbuf *sb, struct g_class *mp, struct g_geom *gp, struct g_provider *pp, struct g_consumer *cp);
 void g_conf_cat_escaped(struct sbuf *sb, const char *buf);
-void g_conf_printf_escaped(struct sbuf *sb, const char *fmt, ...);
+void g_conf_printf_escaped(struct sbuf *sb, const char *fmt, ...) __printflike(2, 3);
 void g_confdot(void *, int flag);
 void g_conftxt(void *, int flag);
 
@@ -73,6 +86,7 @@
 extern struct class_list_head g_classes;
 extern char *g_wait_event, *g_wait_sim, *g_wait_up, *g_wait_down;
 void g_wither_washer(void);
+void g_dbg_printf(const char *gcls, int lvl, struct bio *bp, const char *format, ...) __printflike(4, 5);
 
 /* geom_io.c */
 void g_io_init(void);
Index: sys/geom/geom_io.c
===================================================================
--- sys/geom/geom_io.c
+++ sys/geom/geom_io.c
@@ -49,6 +49,7 @@
 #include <sys/bio.h>
 #include <sys/ktr.h>
 #include <sys/proc.h>
+#include <sys/sbuf.h>
 #include <sys/stack.h>
 #include <sys/sysctl.h>
 #include <sys/vmem.h>
@@ -1030,6 +1031,24 @@
 
 void
 g_print_bio(struct bio *bp)
+{
+#ifndef PRINTF_BUFR_SIZE
+#define PRINTF_BUFR_SIZE 64
+#endif
+	char bufr[PRINTF_BUFR_SIZE];
+	struct sbuf sb, *sbp __unused;
+
+	sbp = sbuf_new(&sb, bufr, sizeof(bufr), SBUF_FIXEDLEN);
+	KASSERT(sbp != NULL, ("sbuf_new misused?"));
+
+	sbuf_set_drain(&sb, sbuf_printf_drain, NULL);
+	g_format_bio(&sb, bp);
+	sbuf_finish(&sb);
+	sbuf_delete(&sb);
+}
+
+void
+g_format_bio(struct sbuf *sb, struct bio *bp)
 {
 	const char *pname, *cmd = NULL;
 
@@ -1041,11 +1060,12 @@
 	switch (bp->bio_cmd) {
 	case BIO_GETATTR:
 		cmd = "GETATTR";
-		printf("%s[%s(attr=%s)]", pname, cmd, bp->bio_attribute);
+		sbuf_printf(sb, "%s[%s(attr=%s)]", pname, cmd,
+		    bp->bio_attribute);
 		return;
 	case BIO_FLUSH:
 		cmd = "FLUSH";
-		printf("%s[%s]", pname, cmd);
+		sbuf_printf(sb, "%s[%s]", pname, cmd);
 		return;
 	case BIO_ZONE: {
 		char *subcmd = NULL;
@@ -1073,7 +1093,7 @@
 			subcmd = "UNKNOWN";
 			break;
 		}
-		printf("%s[%s,%s]", pname, cmd, subcmd);
+		sbuf_printf(sb, "%s[%s,%s]", pname, cmd, subcmd);
 		return;
 	}
 	case BIO_READ:
@@ -1087,9 +1107,9 @@
 		break;
 	default:
 		cmd = "UNKNOWN";
-		printf("%s[%s()]", pname, cmd);
+		sbuf_printf(sb, "%s[%s()]", pname, cmd);
 		return;
 	}
-	printf("%s[%s(offset=%jd, length=%jd)]", pname, cmd,
+	sbuf_printf(sb, "%s[%s(offset=%jd, length=%jd)]", pname, cmd,
 	    (intmax_t)bp->bio_offset, (intmax_t)bp->bio_length);
 }
Index: sys/geom/geom_subr.c
===================================================================
--- sys/geom/geom_subr.c
+++ sys/geom/geom_subr.c
@@ -77,6 +77,43 @@
 	int			post;
 };
 
+void
+g_dbg_printf(const char *gcls, int lvl, struct bio *bp, const char *format,
+    ...)
+{
+#ifndef PRINTF_BUFR_SIZE
+#define PRINTF_BUFR_SIZE 64
+#endif
+	char bufr[PRINTF_BUFR_SIZE];
+	struct sbuf sb, *sbp __unused;
+	va_list ap;
+
+	sbp = sbuf_new(&sb, bufr, sizeof(bufr), SBUF_FIXEDLEN);
+	KASSERT(sbp != NULL, ("sbuf_new misused?"));
+
+	sbuf_set_drain(&sb, sbuf_printf_drain, NULL);
+
+	sbuf_cat(&sb, gcls);
+	if (lvl >= 0)
+		sbuf_printf(&sb, "[%d]", lvl);
+	
+	va_start(ap, format);
+	sbuf_vprintf(&sb, format, ap);
+	va_end(ap);
+
+	if (bp != NULL) {
+		sbuf_putc(&sb, ' ');
+		g_format_bio(&sb, bp);
+	}
+
+	/* Terminate the debug line with a single '\n'. */
+	sbuf_nl_terminate(&sb);
+
+	/* Flush line to printf. */
+	sbuf_finish(&sb);
+	sbuf_delete(&sb);
+}
+
 /*
  * This event offers a new class a chance to taste all preexisting providers.
  */
Index: sys/geom/label/g_label.h
===================================================================
--- sys/geom/label/g_label.h
+++ sys/geom/label/g_label.h
@@ -34,6 +34,7 @@
 #include <sys/endian.h>
 #ifdef _KERNEL
 #include <sys/sysctl.h>
+#include <geom/geom_int.h>
 #endif
 
 #define	G_LABEL_CLASS_NAME	"LABEL"
@@ -50,16 +51,8 @@
 #ifdef _KERNEL
 extern u_int g_label_debug;
 
-#define	G_LABEL_DEBUG(lvl, ...)	do {					\
-	if (g_label_debug >= (lvl)) {					\
-		printf("GEOM_LABEL");					\
-		if (g_label_debug > 0)					\
-			printf("[%u]", lvl);				\
-		printf(": ");						\
-		printf(__VA_ARGS__);					\
-		printf("\n");						\
-	}								\
-} while (0)
+#define G_LABEL_DEBUG(lvl, ...) \
+    _GEOM_DEBUG("GEOM_LABEL", g_label_debug, (lvl), NULL, __VA_ARGS__)
 
 SYSCTL_DECL(_kern_geom_label);
 
Index: sys/geom/mirror/g_mirror.h
===================================================================
--- sys/geom/mirror/g_mirror.h
+++ sys/geom/mirror/g_mirror.h
@@ -34,6 +34,10 @@
 #include <sys/endian.h>
 #include <sys/md5.h>
 
+#ifdef _KERNEL
+#include <geom/geom_int.h>
+#endif
+
 #define	G_MIRROR_CLASS_NAME	"MIRROR"
 
 #define	G_MIRROR_MAGIC		"GEOM::MIRROR"
@@ -86,28 +90,10 @@
 
 extern int g_mirror_debug;
 
-#define	G_MIRROR_DEBUG(lvl, ...)	do {				\
-	if (g_mirror_debug >= (lvl)) {					\
-		printf("GEOM_MIRROR");					\
-		if (g_mirror_debug > 0)					\
-			printf("[%u]", lvl);				\
-		printf(": ");						\
-		printf(__VA_ARGS__);					\
-		printf("\n");						\
-	}								\
-} while (0)
-#define	G_MIRROR_LOGREQ(lvl, bp, ...)	do {				\
-	if (g_mirror_debug >= (lvl)) {					\
-		printf("GEOM_MIRROR");					\
-		if (g_mirror_debug > 0)					\
-			printf("[%u]", lvl);				\
-		printf(": ");						\
-		printf(__VA_ARGS__);					\
-		printf(" ");						\
-		g_print_bio(bp);					\
-		printf("\n");						\
-	}								\
-} while (0)
+#define G_MIRROR_DEBUG(lvl, ...) \
+    _GEOM_DEBUG("GEOM_MIRROR", g_mirror_debug, (lvl), NULL, __VA_ARGS__)
+#define G_MIRROR_LOGREQ(lvl, bp, ...) \
+    _GEOM_DEBUG("GEOM_MIRROR", g_mirror_debug, (lvl), (bp), __VA_ARGS__)
 
 #define	G_MIRROR_BIO_FLAG_REGULAR	0x01
 #define	G_MIRROR_BIO_FLAG_SYNC		0x02