linux-kernel - [PATCH v4 4/5] kdb: Improve handling of characters from different input sources

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Date:   Fri, 25 Oct 2019 08:33:27 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        patches@...aro.org
Subject: [PATCH v4 4/5] kdb: Improve handling of characters from different input sources

Currently if an escape timer is interrupted by a character from a
different input source then the new character is discarded and the
function returns '\e' (which will be discarded by the level above).
It is hard to see why this would ever be the desired behaviour.
Fix this to return the new character rather than the '\e'.

This is a bigger refactor than might be expected because the new
character needs to go through escape sequence detection.

Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
Reviewed-by: Douglas Anderson <dianders@...omium.org>
---
 kernel/debug/kdb/kdb_io.c | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 9b6933d585b5..f794c0ca4557 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -127,10 +127,10 @@ char kdb_getchar(void)
 {
 #define ESCAPE_UDELAY 1000
 #define ESCAPE_DELAY (2*1000000/ESCAPE_UDELAY) /* 2 seconds worth of udelays */
-	char escape_data[5];	/* longest vt100 escape sequence is 4 bytes */
-	char *ped = escape_data;
+	char buf[4];	/* longest vt100 escape sequence is 4 bytes */
+	char *pbuf = buf;
 	int escape_delay = 0;
-	get_char_func *f, *f_escape = NULL;
+	get_char_func *f, *f_prev = NULL;
 	int key;
 
 	for (f = &kdb_poll_funcs[0]; ; ++f) {
@@ -150,26 +150,26 @@ char kdb_getchar(void)
 			continue;
 		}
 
-		if (escape_delay == 0 && key == '\e') {
+		/*
+		 * When the first character is received (or we get a change
+		 * input source) we set ourselves up to handle an escape
+		 * sequences (just in case).
+		 */
+		if (f_prev != f) {
+			f_prev = f;
+			pbuf = buf;
 			escape_delay = ESCAPE_DELAY;
-			ped = escape_data;
-			f_escape = f;
-		}
-		if (escape_delay) {
-			if (f_escape != f)
-				return '\e';
-
-			*ped++ = key;
-			key = kdb_handle_escape(escape_data, ped - escape_data);
-			if (key < 0)
-				return '\e';
-			if (key == 0)
-				continue;
 		}
 
-		break;	/* A key to process */
+		*pbuf++ = key;
+		key = kdb_handle_escape(buf, pbuf - buf);
+		if (key < 0) /* no escape sequence; return first character */
+			return buf[0];
+		if (key > 0)
+			return key;
 	}
-	return key;
+
+	unreachable();
 }
 
 /*
-- 
2.21.0