Fix to virtual terminal UTF-8 mode handling

This patch fixes a bug in the virtual terminal driver, whereby the UTF-8 mode is reset to "off" following a console reset, such as might be delivered by mingetty, screen, vim, etc...

Rather than resetting to hardcoded "0", it gets reset on or off, as determined by a new sysctl located in /proc/tty/vt/default_utf8_mode. This patch is best accompanied with an addition of the following line to the system's init scripts:

echo 1 >/proc/tty/vt/default_utf8_mode

Following this, all resets to the console will leave it with UTF-8 mode on.

The default behaviour of this sysctl is as before, without the patch. Namely, UTF-8 mode is switched off on reset. [I.e applying this patch does not affect default behaviour].

--- linux-2.6.11/drivers/char/vt.c 2005-05-04 02:01:08.000000000
+0100 +++ linux-2.6.11-utfswitch/drivers/char/vt.c 2005-05-07
22:41:58.000000000 +0100 @@ -93,6 +93,7 @@
#include <linux/pm.h>
#include <linux/font.h>
#include <linux/bitops.h>
+#include <linux/proc_fs.h>

#include <asm/io.h>
#include <asm/system.h>
@@ -162,6 +163,15 @@
static int blankinterval = 10*60*HZ;
static int vesa_off_interval;

+/*
+ * When resetting a console, do we start in UTF-8 mode or not?
+ * 0 = no, 1 = yes
+ */
+static int default_utf8_mode = 0;
+
+struct proc_dir_entry *proc_vt_dir;
+struct proc_dir_entry *proc_default_utf8_mode;
+
static DECLARE_WORK(console_work, console_callback, NULL);

/*
@@ -1472,7 +1482,7 @@
charset = 0;
need_wrap = 0;
report_mouse = 0;

-	utf             = 0;
+	utf             = default_utf8_mode;
 	utf_count       = 0;

disp_ctrl = 0;
@@ -2530,6 +2540,63 @@
reset_terminal(currcons, do_clear);
}

+static int proc_write_default_utf8_mode(struct file *file, const char *buffer,
+ unsigned long count, void *data)
+{
+ char temp[16];
+ int len;
+
+ if (count > sizeof(temp)-1)
+ len = sizeof(temp)-1;
+ else
+ len = count;
+
+ if (copy_from_user(temp, buffer, len))
+ return -EFAULT;
+
+ temp[len] = 0;
+
+ /* No effect if empty or >1 character long */
+ if (temp[0] == 0 || (temp[1] != '\n' && temp[1] != 0)) {
+ return len;
+ }
+
+ /* No effect if outside the range 0<=x<=1 */
+ if (temp[0] < '0' || temp[0] > '1') {
+ return len;
+ }
+
+ default_utf8_mode = (temp[0] - '0');
+
+ return len;
+}
+
+static int proc_read_default_utf8_mode(char *page, char **start, off_t off,
+ int count, int *eof, void *data)
+{
+ return sprintf(page, "default_utf8_mode = %d\n",
default_utf8_mode); +}
+
+static int init_proc(void)
+{
+ proc_vt_dir = proc_mkdir("tty/vt", NULL);
+
+ if (!proc_vt_dir)
+ return -ENOMEM;
+
+ proc_default_utf8_mode = create_proc_entry("default_utf8_mode",
0644, proc_vt_dir); +
+ if (!proc_default_utf8_mode)
+ return -ENOMEM;
+
+ proc_default_utf8_mode->owner = THIS_MODULE;
+ proc_default_utf8_mode->data = &default_utf8_mode;
+ proc_default_utf8_mode->write_proc =
proc_write_default_utf8_mode;
+ proc_default_utf8_mode->read_proc = proc_read_default_utf8_mode;
+
+ return 0;
+}
+
/*
* This routine initializes console interrupts, and does nothing
* else. If you want the screen to clear, call tty_write with
@@ -2612,6 +2679,8 @@

int __init vty_init(void)
{
+ int ret;
+
vcs_init();

console_driver = alloc_tty_driver(MAX_NR_CONSOLES);
@@ -2638,6 +2707,11 @@
#ifdef CONFIG_MDA_CONSOLE
mda_console_init();
#endif
+
+ ret = init_proc();
+ if (ret)
+ return ret;
+
return 0;
}

Paul "LeoNerd" Evans

[email protected]
ICQ# 4135350       |  Registered Linux# 179460
http://www.leonerd.org.uk/

Apologies, my mail client annoyingly wrapped the patch; here it is fixed.

diff -urN --exclude-from=diff-exclude linux-2.6.11/drivers/char/vt.c linux-2.6.11-utfswitch/drivers/char/vt.c
@@ -93,6 +93,7 @@
 #include <linux/pm.h>
 #include <linux/font.h>
 #include <linux/bitops.h>
+#include <linux/proc_fs.h>
 
 #include <asm/io.h>
 #include <asm/system.h>

@@ -162,6 +163,15 @@
 static int blankinterval = 10*60*HZ;
 static int vesa_off_interval;
 
+/*
+ * When resetting a console, do we start in UTF-8 mode or not?
+ * 0 = no, 1 = yes
+ */
+static int default_utf8_mode = 0;
+
+struct proc_dir_entry *proc_vt_dir;
+struct proc_dir_entry *proc_default_utf8_mode;
+
 static DECLARE_WORK(console_work, console_callback, NULL);
 
 /*

@@ -1472,7 +1482,7 @@
 	charset		= 0;
 	need_wrap	= 0;
 	report_mouse	= 0;
-	utf             = 0;
+	utf             = default_utf8_mode;
 	utf_count       = 0;
 
 	disp_ctrl	= 0;

@@ -2530,6 +2540,63 @@
 	reset_terminal(currcons, do_clear);
 }
 
+static int proc_write_default_utf8_mode(struct file *file, const char *buffer,
+			unsigned long count, void *data)
+{
+	char temp[16];
+	int len;
+
+	if (count > sizeof(temp)-1)
+		len = sizeof(temp)-1;
+	else
+		len = count;
+
+	if (copy_from_user(temp, buffer, len))
+		return -EFAULT;
+
+	temp[len] = 0;
+
+	/* No effect if empty or >1 character long */
+	if (temp[0] == 0 || (temp[1] != '\n' && temp[1] != 0)) {
+		return len;
+	}
+
+	/* No effect if outside the range 0<=x<=1 */
+	if (temp[0] < '0' || temp[0] > '1') {
+		return len;
+	}
+
+	default_utf8_mode = (temp[0] - '0');
+
+	return len;
+}
+
+static int proc_read_default_utf8_mode(char *page, char **start, off_t off,
+			int count, int *eof, void *data)
+{
+	return sprintf(page, "default_utf8_mode = %d\n", default_utf8_mode);
+}
+
+static int init_proc(void)
+{
+	proc_vt_dir = proc_mkdir("tty/vt", NULL);
+
+	if (!proc_vt_dir)
+		return -ENOMEM;
+
+	proc_default_utf8_mode = create_proc_entry("default_utf8_mode", 0644, proc_vt_dir);
+
+	if (!proc_default_utf8_mode)
+		return -ENOMEM;
+
+	proc_default_utf8_mode->owner = THIS_MODULE;
+	proc_default_utf8_mode->data = &default_utf8_mode;
+	proc_default_utf8_mode->write_proc = proc_write_default_utf8_mode;
+	proc_default_utf8_mode->read_proc = proc_read_default_utf8_mode;
+
+	return 0;
+}
+
 /*
  * This routine initializes console interrupts, and does nothing
  * else. If you want the screen to clear, call tty_write with

@@ -2612,6 +2679,8 @@
 
 int __init vty_init(void)
 {
+	int ret;
+
 	vcs_init();
 
 	console_driver = alloc_tty_driver(MAX_NR_CONSOLES);

@@ -2638,6 +2707,11 @@
 #ifdef CONFIG_MDA_CONSOLE
 	mda_console_init();
 #endif
+
+	ret = init_proc();
+	if (ret)
+		return ret;
+
 	return 0;
 }
 

Paul "LeoNerd" Evans

[email protected]
ICQ# 4135350       |  Registered Linux# 179460
http://www.leonerd.org.uk/

Is it a bug? What did earlier kernels do? 2.4.x?

Presumably userspace knows what mode the user wants the terminal to be using. Shouldn't userspace be resetting that mode after a reset?

I'd be inclined to think that this is more of a terminfo issue. If you want your terminal to reset into UTF-8, use a terminfo entry with the appropriate command string instead of the current one - this would be the 'rs1' capability:

rs1=\Ec\E]R

That's reset console to default, reset palette.

There's no standard way to represent this in userspace. But yeah.

Daniel Jacobowitz
CodeSourcery, LLC

Unfortunately, that doesn't work. Doing it that way means that any program running on a host whose terminfo is so configured, would force UTF-8 mode on, when it issues a reset to a Linux console, regardless of which machine that is on (e.g. telnet, ssh,...). Furthermore, it would do so regardless of whether we want UTF-8 mode, or not. Again with my patch it is a user configurable matter whether they want UTF-8 or not. This terminfo entry forces it to happen.

That said, I am planning a whole bunch of other changes to terminfo; my repeated wrestling with xterm recently on the regard of modified cursor keys (e.g. Ctrl+left) has lead me to conclude the whole system needs a bit of an overhaul... But that's somewhat off-topic to the kernel.. :)

Paul "LeoNerd" Evans

[email protected]
ICQ# 4135350       |  Registered Linux# 179460
http://www.leonerd.org.uk/

I haven't checked earlier 2.4 kernels, but I know the 2.6 ones have done this for quite some time; a good year or so at least.

Well, that does require changes to a lot of the programs that talk to the console, moreover, they now need to be sensitive to whether it is in UTF-8 mode, where previously they did not. E.g. consider mingetty...

Also, as I understand it, there is one keyboard map, and one console font for the entire virtual console system - either they are UTF-8, or not. It doesn't really make sense to be switching these about.

Moreover, this code also affects dynamic creation of new virtual consoles. E.g. when debian's "oh no, I can't start the X server" ncurses dialog appears, without my patch it prints UTF-8 characters on a new console, tty8, on a console that isn't set to display them, and mass breakage results. Now, it all happens cleanly, because the new console is already in UTF-8 mode.

Were this to be pushed to userland, every program that outputs data would need to detect the UTF-8 mode of the console, and set it appropriately. Moreover, they would need to perform this logic only on a Linux virtual console; such things as XTerm or Gnome-terminal do it automatically.

Paul "LeoNerd" Evans

[email protected]
ICQ# 4135350       |  Registered Linux# 179460
http://www.leonerd.org.uk/