preload: add "show preload" DDB command

This is the DDB equivalent of the debug.dump_modinfo sysctl which
outputs pretty-printed bootloader metadata.

Move sbuf_db_printf_drain to subr_prf.c and expose it for general use.

Reviewed By: jmg
Differential Revision: https://reviews.freebsd.org/D53763

sys/kern/subr_module.c

@@ -28,6 +28,9 @@
  * SUCH DAMAGE.
  */
 
+#include <sys/cdefs.h>
+#include "opt_ddb.h"
+
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/linker.h>
@@ -39,6 +42,10 @@
 #include <vm/vm.h>
 #include <vm/vm_extern.h>
 
+#ifdef DDB
+#include <ddb/ddb.h>
+#endif
+
 /*
  * Preloaded module support
  */
@@ -607,3 +614,16 @@ SYSCTL_PROC(_debug, OID_AUTO, dump_modinfo,
     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_preload_dump, "A",
     "pretty-print the bootloader metadata");
+
+#ifdef DDB
+DB_SHOW_COMMAND_FLAGS(preload, db_show_preload, DB_CMD_MEMSAFE)
+{
+	struct sbuf sb;
+	char buffer[128];
+
+	sbuf_new(&sb, buffer, sizeof(buffer), SBUF_FIXEDLEN);
+	sbuf_set_drain(&sb, sbuf_db_printf_drain, NULL);
+	preload_dump_internal(&sb);
+	sbuf_finish(&sb);
+}
+#endif

sys/kern/subr_prf.c

@@ -1358,3 +1358,12 @@ sbuf_printf_drain(void *arg, const char *data, int len)
 
 	return (r);
 }
+
+#if defined(_KERNEL) && defined(DDB)
+int
+sbuf_db_printf_drain(void *arg __unused, const char *data, int len)
+{
+
+	return (db_printf("%.*s", len, data));
+}
+#endif

sys/kern/subr_witness.c

@@ -3121,12 +3121,6 @@ sysctl_debug_witness_badstacks(SYSCTL_HANDLER_ARGS)
 }
 
 #ifdef DDB
-static int
-sbuf_db_printf_drain(void *arg __unused, const char *data, int len)
-{
-	return (db_printf("%.*s", len, data));
-}
-
 DB_SHOW_COMMAND_FLAGS(badstacks, db_witness_badstacks, DB_CMD_MEMSAFE)
 {
 	struct sbuf sb;

sys/sys/sbuf.h

@@ -114,6 +114,9 @@ struct uio;
 struct sbuf	*sbuf_uionew(struct sbuf *, struct uio *, int *);
 int		 sbuf_bcopyin(struct sbuf *, const void *, size_t);
 int		 sbuf_copyin(struct sbuf *, const void *, size_t);
+#ifdef DDB
+int		 sbuf_db_printf_drain(void *arg, const char *data, int len);
+#endif
 #endif
 __END_DECLS