1 files changed, 18 insertions, 13 deletions

diff --git a/sys/ddb/db_capture.c b/sys/ddb/db_capture.c
index 5a4cb37a9bc11..75da64edd11a7 100644
--- a/sys/ddb/db_capture.c
+++ b/sys/ddb/db_capture.c
@@ -32,6 +32,8 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_ddb.h"
+
 #include <sys/param.h>
 #include <sys/conf.h>
 #include <sys/kernel.h>
@@ -52,11 +54,19 @@ __FBSDID("$FreeBSD$");
  * kernel dumper routines without restarting the kernel, which is undesirable
  * in the midst of debugging.  Instead, we maintain a large static global
  * buffer that we fill from DDB's output routines.
+ *
+ * We enforce an invariant at runtime that buffer sizes are even multiples of
+ * the textdump block size, which is a design choice that we might want to
+ * reconsider.
  */
 static MALLOC_DEFINE(M_DDB_CAPTURE, "ddb_capture", "DDB capture buffer");
 
+#ifndef DDB_CAPTURE_DEFAULTBUFSIZE
 #define	DDB_CAPTURE_DEFAULTBUFSIZE	48*1024
+#endif
+#ifndef DDB_CAPTURE_MAXBUFSIZE
 #define	DDB_CAPTURE_MAXBUFSIZE	512*1024
+#endif
 #define	DDB_CAPTURE_FILENAME	"ddb.txt"	/* Captured DDB output. */
 
 static char *db_capture_buf;
@@ -81,24 +91,19 @@ SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, maxbufsize, CTLFLAG_RD,
     "Maximum value for debug.ddb.capture.bufsize");
 
 /*
- * Various compile-time assertions: defaults must be even multiples of
- * textdump block size.  We also perform run-time checking of
- * user-configurable values.
- */
-CTASSERT(DDB_CAPTURE_DEFAULTBUFSIZE % TEXTDUMP_BLOCKSIZE == 0);
-CTASSERT(DDB_CAPTURE_MAXBUFSIZE % TEXTDUMP_BLOCKSIZE == 0);
-
-/*
- * Boot-time allocation of the DDB capture buffer, if any.
+ * Boot-time allocation of the DDB capture buffer, if any.  Force all buffer
+ * sizes, including the maximum size, to be rounded to block sizes.
  */
 static void
 db_capture_sysinit(__unused void *dummy)
 {
 
 	TUNABLE_INT_FETCH("debug.ddb.capture.bufsize", &db_capture_bufsize);
+	db_capture_maxbufsize = roundup(db_capture_maxbufsize,
+	    TEXTDUMP_BLOCKSIZE);
 	db_capture_bufsize = roundup(db_capture_bufsize, TEXTDUMP_BLOCKSIZE);
-	if (db_capture_bufsize > DDB_CAPTURE_MAXBUFSIZE)
-		db_capture_bufsize = DDB_CAPTURE_MAXBUFSIZE;
+	if (db_capture_bufsize > db_capture_maxbufsize)
+		db_capture_bufsize = db_capture_maxbufsize;
 	if (db_capture_bufsize != 0)
 		db_capture_buf = malloc(db_capture_bufsize, M_DDB_CAPTURE,
 		    M_WAITOK);
@@ -121,7 +126,7 @@ sysctl_debug_ddb_capture_bufsize(SYSCTL_HANDLER_ARGS)
 	if (error || req->newptr == NULL)
 		return (error);
 	size = roundup(size, TEXTDUMP_BLOCKSIZE);
-	if (size > DDB_CAPTURE_MAXBUFSIZE)
+	if (size > db_capture_maxbufsize)
 		return (EINVAL);
 	sx_xlock(&db_capture_sx);
 	if (size != 0) {
@@ -150,7 +155,7 @@ sysctl_debug_ddb_capture_bufsize(SYSCTL_HANDLER_ARGS)
 
 	KASSERT(db_capture_bufoff <= db_capture_bufsize,
 	    ("sysctl_debug_ddb_capture_bufsize: bufoff > bufsize"));
-	KASSERT(db_capture_bufsize <= DDB_CAPTURE_MAXBUFSIZE,
+	KASSERT(db_capture_bufsize <= db_capture_maxbufsize,
 	    ("sysctl_debug_ddb_capture_maxbufsize: bufsize > maxbufsize"));
 
 	return (0);