linux-kernel - [ 32/62] kdb,vt_console: Fix missed data due to pager overruns

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Message-Id: <20121019024301.172251728@linuxfoundation.org>
Date:	Thu, 18 Oct 2012 19:45:00 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Jason Wessel <jason.wessel@...driver.com>
Subject: [ 32/62] kdb,vt_console: Fix missed data due to pager overruns

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wessel <jason.wessel@...driver.com>

commit 17b572e82032bc246324ce136696656b66d4e3f1 upstream.

It is possible to miss data when using the kdb pager.  The kdb pager
does not pay attention to the maximum column constraint of the screen
or serial terminal.  This result is not incrementing the shown lines
correctly and the pager will print more lines that fit on the screen.
Obviously that is less than useful when using a VGA console where you
cannot scroll back.

The pager will now look at the kdb_buffer string to see how many
characters are printed.  It might not be perfect considering you can
output ASCII that might move the cursor position, but it is a
substantially better approximation for viewing dmesg and trace logs.

This also means that the vt screen needs to set the kdb COLUMNS
variable.

Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/vt/vt.c       |   13 +++++++++++++
 kernel/debug/kdb/kdb_io.c |   33 ++++++++++++++++++++++++++++-----
 2 files changed, 41 insertions(+), 5 deletions(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3475,6 +3475,19 @@ int con_debug_enter(struct vc_data *vc)
 			kdb_set(2, setargs);
 		}
 	}
+	if (vc->vc_cols < 999) {
+		int colcount;
+		char cols[4];
+		const char *setargs[3] = {
+			"set",
+			"COLUMNS",
+			cols,
+		};
+		if (kdbgetintenv(setargs[0], &colcount)) {
+			snprintf(cols, 4, "%i", vc->vc_cols);
+			kdb_set(2, setargs);
+		}
+	}
 #endif /* CONFIG_KGDB_KDB */
 	return ret;
 }
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -552,6 +552,7 @@ int vkdb_printf(const char *fmt, va_list
 {
 	int diag;
 	int linecount;
+	int colcount;
 	int logging, saved_loglevel = 0;
 	int saved_trap_printk;
 	int got_printf_lock = 0;
@@ -584,6 +585,10 @@ int vkdb_printf(const char *fmt, va_list
 	if (diag || linecount <= 1)
 		linecount = 24;
 
+	diag = kdbgetintenv("COLUMNS", &colcount);
+	if (diag || colcount <= 1)
+		colcount = 80;
+
 	diag = kdbgetintenv("LOGGING", &logging);
 	if (diag)
 		logging = 0;
@@ -690,7 +695,7 @@ kdb_printit:
 		gdbstub_msg_write(kdb_buffer, retlen);
 	} else {
 		if (dbg_io_ops && !dbg_io_ops->is_console) {
-			len = strlen(kdb_buffer);
+			len = retlen;
 			cp = kdb_buffer;
 			while (len--) {
 				dbg_io_ops->write_char(*cp);
@@ -709,11 +714,29 @@ kdb_printit:
 		printk(KERN_INFO "%s", kdb_buffer);
 	}
 
-	if (KDB_STATE(PAGER) && strchr(kdb_buffer, '\n'))
-		kdb_nextline++;
+	if (KDB_STATE(PAGER)) {
+		/*
+		 * Check printed string to decide how to bump the
+		 * kdb_nextline to control when the more prompt should
+		 * show up.
+		 */
+		int got = 0;
+		len = retlen;
+		while (len--) {
+			if (kdb_buffer[len] == '\n') {
+				kdb_nextline++;
+				got = 0;
+			} else if (kdb_buffer[len] == '\r') {
+				got = 0;
+			} else {
+				got++;
+			}
+		}
+		kdb_nextline += got / (colcount + 1);
+	}
 
 	/* check for having reached the LINES number of printed lines */
-	if (kdb_nextline == linecount) {
+	if (kdb_nextline >= linecount) {
 		char buf1[16] = "";
 #if defined(CONFIG_SMP)
 		char buf2[32];
@@ -776,7 +799,7 @@ kdb_printit:
 			kdb_grepping_flag = 0;
 			kdb_printf("\n");
 		} else if (buf1[0] == ' ') {
-			kdb_printf("\n");
+			kdb_printf("\r");
 			suspend_grep = 1; /* for this recursion */
 		} else if (buf1[0] == '\n') {
 			kdb_nextline = linecount - 1;


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