linux-kernel - [PATCH v3 4/5] kdb: Improve handling of characters from different input sources

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Date:   Mon, 14 Oct 2019 16:46:25 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Jason Wessel <jason.wessel@...driver.com>,
        Douglas Anderson <dianders@...omium.org>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        patches@...aro.org
Subject: [PATCH v3 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>
---
 kernel/debug/kdb/kdb_io.c | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 39476616295e..f9839566c7d6 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -125,10 +125,10 @@ 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) {
@@ -148,27 +148,26 @@ 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