linux-kernel - [PATCH v2 4/5] kdb: Improve handling of characters from different input sources

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Message-Id: <20191008132043.7966-5-daniel.thompson@linaro.org>
Date:   Tue,  8 Oct 2019 14:20:42 +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 v2 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 then the '\e'.

This is a bigger refactor that 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 | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index a9e73bc9d1c3..288dd1babf90 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -122,8 +122,8 @@ static int 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;
 	int key;
@@ -145,27 +145,26 @@ static int kdb_getchar(void)
 			continue;
 		}
 
-		if (escape_delay == 0 && key == '\e') {
-			escape_delay = ESCAPE_DELAY;
-			ped = escape_data;
+		/*
+		 * 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_escape != f) {
 			f_escape = f;
-		}
-		if (escape_delay) {
-			if (f_escape != f)
-				return '\e';
-
-			*ped++ = key;
-			key = kdb_read_handle_escape(escape_data,
-						     ped - escape_data);
-			if (key < 0)
-				return '\e';
-			if (key == 0)
-				continue;
+			pbuf = buf;
+			escape_delay = ESCAPE_DELAY;
 		}
 
-		break;	/* A key to process */
+		*pbuf++ = key;
+		key = kdb_read_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