Add a drain function for struct sysctl_req, and use it for a variety of

handlers, some of which had to do awkward things to get a large enough
FIXEDLEN buffer.

Note that some sysctl handlers were explicitly outputting a trailing NUL
byte.  This behaviour was preserved, though it should not be necessary.

Reviewed by:	phk

1 files changed, 3 insertions, 14 deletions

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index 201be99..3fec4c4 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -154,8 +154,7 @@ __FBSDID("$FreeBSD$");
 #define	MAX_W_NAME	64
 
 #define	BADSTACK_SBUF_SIZE	(256 * WITNESS_COUNT)
-#define	CYCLEGRAPH_SBUF_SIZE	8192
-#define	FULLGRAPH_SBUF_SIZE	32768
+#define	FULLGRAPH_SBUF_SIZE	512
 
 /*
  * These flags go in the witness relationship matrix and describe the
@@ -2545,7 +2544,7 @@ sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS)
 		return (error);
 	}
 	error = 0;
-	sb = sbuf_new(NULL, NULL, FULLGRAPH_SBUF_SIZE, SBUF_FIXEDLEN);
+	sb = sbuf_new_for_sysctl(NULL, NULL, FULLGRAPH_SBUF_SIZE, req);
 	if (sb == NULL)
 		return (ENOMEM);
 	sbuf_printf(sb, "\n");
@@ -2558,19 +2557,9 @@ sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS)
 	mtx_unlock_spin(&w_mtx);
 
 	/*
-	 * While using SBUF_FIXEDLEN, check if the sbuf overflowed.
-	 */
-	if (sbuf_overflowed(sb)) {
-		sbuf_delete(sb);
-		panic("%s: sbuf overflowed, bump FULLGRAPH_SBUF_SIZE value\n",
-		    __func__);
-	}
-
-	/*
 	 * Close the sbuf and return to userland.
 	 */
-	sbuf_finish(sb);
-	error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
+	error = sbuf_finish(sb);
 	sbuf_delete(sb);
 
 	return (error);