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From: "Justin T. Gibbs" <gibbs@FreeBSD.org>
Date: Tue, 14 Jun 2011 21:37:25 +0000 (UTC)
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Subject: svn commit: r223099 - head/sys/kern
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Author: gibbs
Date: Tue Jun 14 21:37:25 2011
New Revision: 223099
URL: http://svn.freebsd.org/changeset/base/223099

Log:
  sys/kern/subr_kdb.c:
  	Modify the "alternate break sequence" detecting state
  	machine so that only a contiguous invocation of the
  	break sequence is accepted.  The old implementation
  	did not reset the state machine when detecting an
  	unexpected character.
  
  	While here, use an enum for the states of the machine
  	instead of magic numbers.bmitted by:
  
  Sponsored by:	Spectra Logic Corporation

Modified:
  head/sys/kern/subr_kdb.c

Modified: head/sys/kern/subr_kdb.c
==============================================================================
--- head/sys/kern/subr_kdb.c	Tue Jun 14 20:30:49 2011	(r223098)
+++ head/sys/kern/subr_kdb.c	Tue Jun 14 21:37:25 2011	(r223099)
@@ -244,29 +244,44 @@ kdb_reboot(void)
 #define	KEY_CRTLP	16	/* ^P */
 #define	KEY_CRTLR	18	/* ^R */
 
+/* States of th KDB "alternate break sequence" detecting state machine. */
+enum {
+	KDB_ALT_BREAK_SEEN_NONE,
+	KDB_ALT_BREAK_SEEN_CR,
+	KDB_ALT_BREAK_SEEN_CR_TILDE,
+};
+
 int
 kdb_alt_break(int key, int *state)
 {
 	int brk;
 
+	/* All states transition to KDB_ALT_BREAK_SEEN_CR on a CR. */
+	if (key == KEY_CR) {
+		*state = KDB_ALT_BREAK_SEEN_CR;
+		return (0);
+	}
+
 	brk = 0;
 	switch (*state) {
-	case 0:
-		if (key == KEY_CR)
-			*state = 1;
-		break;
-	case 1:
+	case KDB_ALT_BREAK_SEEN_CR:
+		*state = KDB_ALT_BREAK_SEEN_NONE;
 		if (key == KEY_TILDE)
-			*state = 2;
+			*state = KDB_ALT_BREAK_SEEN_CR_TILDE;
 		break;
-	case 2:
+	case KDB_ALT_BREAK_SEEN_CR_TILDE:
+		*state = KDB_ALT_BREAK_SEEN_NONE;
 		if (key == KEY_CRTLB)
 			brk = KDB_REQ_DEBUGGER;
 		else if (key == KEY_CRTLP)
 			brk = KDB_REQ_PANIC;
 		else if (key == KEY_CRTLR)
 			brk = KDB_REQ_REBOOT;
-		*state = 0;
+		break;
+	case KDB_ALT_BREAK_SEEN_NONE:
+	default:
+		*state = KDB_ALT_BREAK_SEEN_NONE;
+		break;
 	}
 	return (brk);
 }